Bounce buffer for mds client decryption when vmalloc()

ceph_fname_to_usr() needs a temporary buffer for some operations (currently only base64-decoding ciphertext) and it is convenient to allow the caller to specify this buffer to avoid a heap allocation, so it has a (nullable) tname argument. Until now, this argument was a struct fscrypt_str; however, this is unnecessary for two reasons:

1. tname->len isn't used anywhere: ceph_fname_to_usr() assumes a buffer large enough to hold the ciphertext, and parse_reply_info_readdir() -- the only caller to use tname -- doesn't set it.
2. While the tname parameter is documented "may be NULL," parse_reply_info_readdir() always passes it but with tname->name sometimes NULL in violation of the contract, indicating that the unnecessary container creates actual confusion.

Therefore, change the type to unsigned char * and pass the buffer directly.

Signed-off-by Sam Edwards <[email protected]>

---
 fs/ceph/crypto.c     | 10 +++++-----
 fs/ceph/crypto.h     |  4 ++--
 fs/ceph/mds_client.c |  6 +++---
 3 files changed, 10 insertions(+), 10 deletions(-)

fs/ceph/crypto.c +0 -0

index 64d240759277..7515cb251226 100644

fs/ceph/crypto.c +4 -4

 		      struct fscrypt_str *oname, bool *is_nokey)
 {
 	struct inode *dir = fname->dir;

@@ -357,16 +357,16 @@ int ceph_fname_to_usr(const struct ceph_fname *fname, struct fscrypt_str *tname,
 			ret = fscrypt_fname_alloc_buffer(NAME_MAX, &_tname);
 			if (ret)
 				goto out_inode;
-			tname = &_tname;
+			tname = _tname.name;
 		}
 
-		declen = base64_decode(name, name_len,
-				       tname->name, false, BASE64_IMAP);
+		declen = base64_decode(name, name_len, tname, false,
+				       BASE64_IMAP);
 		if (declen <= 0) {
 			ret = -EIO;
 			goto out;
 		}
-		iname.name = tname->name;
+		iname.name = tname;
 		iname.len = declen;
 	} else {
 		iname.name = fname->ctext;

fs/ceph/crypto.h +2 -2

index b748e2060bc9..79cb563fd887 100644
@@ -115,7 +115,7 @@ static inline void ceph_fname_free_buffer(struct inode *parent,
 		fscrypt_fname_free_buffer(fname);
 }
 
-int ceph_fname_to_usr(const struct ceph_fname *fname, struct fscrypt_str *tname,
+int ceph_fname_to_usr(const struct ceph_fname *fname, unsigned char *tname,
 		      struct fscrypt_str *oname, bool *is_nokey);
 int ceph_fscrypt_prepare_readdir(struct inode *dir);
 

@@ -204,7 +204,7 @@ static inline void ceph_fname_free_buffer(struct inode *parent,
 }
 
 static inline int ceph_fname_to_usr(const struct ceph_fname *fname,
-				    struct fscrypt_str *tname,
+				    unsigned char *tname,
 				    struct fscrypt_str *oname, bool *is_nokey)
 {
 	oname->name = fname->name;

fs/ceph/mds_client.c +3 -3

index ed17e0023705..aa6730b48e97 100644
@@ -488,11 +488,11 @@ static int parse_reply_info_readdir(void **p, void *end,
 		struct inode *inode = d_inode(req->r_dentry);
 		struct ceph_inode_info *ci = ceph_inode(inode);
 		struct ceph_mds_reply_dir_entry *rde = info->dir_entries + i;
-		struct fscrypt_str tname = FSTR_INIT(NULL, 0);
 		struct fscrypt_str oname = FSTR_INIT(NULL, 0);
 		struct ceph_fname fname;
 		u32 altname_len, _name_len;
 		u8 *altname, *_name;
+		u8 *tname = NULL;
 
 		/* dentry */
 		ceph_decode_32_safe(p, end, _name_len, bad);

@@ -540,7 +540,7 @@ static int parse_reply_info_readdir(void **p, void *end,
 			 * always be shorter, which is 3/4 of origin
 			 * string.
 			 */
-			tname.name = _name;
+			tname = _name;
 
 			/*
 			 * Set oname to _name too, and this will be

@@ -557,7 +557,7 @@ static int parse_reply_info_readdir(void **p, void *end,
 			oname.len = altname_len;
 		}
 		rde->is_nokey = false;
-		err = ceph_fname_to_usr(&fname, &tname, &oname, &rde->is_nokey);
+		err = ceph_fname_to_usr(&fname, tname, &oname, &rde->is_nokey);
 		if (err) {
 			pr_err_client(cl, "unable to decode %.*s, got %d\n",
 				      _name_len, _name, err);

Quoted 25 lines · On Tue, 26 May 2026 19:58:27 -0700 Sam Edwards <[email protected]> wrote:

ceph_fname_to_usr() needs a temporary buffer for some operations (currently only base64-decoding ciphertext) and it is convenient to allow the caller to specify this buffer to avoid a heap allocation, so it has a (nullable) tname argument. Until now, this argument was a struct fscrypt_str; however, this is unnecessary for two reasons:

1. tname->len isn't used anywhere: ceph_fname_to_usr() assumes a buffer large enough to hold the ciphertext, and parse_reply_info_readdir() -- the only caller to use tname -- doesn't set it.
2. While the tname parameter is documented "may be NULL," parse_reply_info_readdir() always passes it but with tname->name sometimes NULL in violation of the contract, indicating that the unnecessary container creates actual confusion.

Therefore, change the type to unsigned char * and pass the buffer directly.

Signed-off-by Sam Edwards <[email protected]>

---
 fs/ceph/crypto.c     | 10 +++++-----
 fs/ceph/crypto.h     |  4 ++--
 fs/ceph/mds_client.c |  6 +++---
 3 files changed, 10 insertions(+), 10 deletions(-)

fs/ceph/crypto.c int ceph_encode_encrypted_dname(struct inode *parent, char *buf, int elen) · line 303

Quoted 10 lines

fs/ceph/crypto.c +1 -1

index 64d240759277..7515cb251226 100644
@@ -300,7 +300,7 @@ int ceph_encode_encrypted_dname(struct inode *parent, char *buf, int elen)
  *
  * Returns 0 on success or negative error code on error.
  */
-int ceph_fname_to_usr(const struct ceph_fname *fname, struct fscrypt_str *tname,
+int ceph_fname_to_usr(const struct ceph_fname *fname, unsigned char *tname,

I can't help feeling that the buffer length should also be passed. Either explicitly or, if constant, implicitly by embedding the array in a structure.

-- David

Quoted 81 lines

fs/ceph/crypto.c +4 -4

                    struct fscrypt_str *oname, bool *is_nokey)
 {
      struct inode *dir = fname->dir;

@@ -357,16 +357,16 @@ int ceph_fname_to_usr(const struct ceph_fname *fname, struct fscrypt_str *tname,
                      ret = fscrypt_fname_alloc_buffer(NAME_MAX, &_tname);
                      if (ret)
                              goto out_inode;
-                     tname = &_tname;
+                     tname = _tname.name;
              }
 
-             declen = base64_decode(name, name_len,
-                                    tname->name, false, BASE64_IMAP);
+             declen = base64_decode(name, name_len, tname, false,
+                                    BASE64_IMAP);
              if (declen <= 0) {
                      ret = -EIO;
                      goto out;
              }
-             iname.name = tname->name;
+             iname.name = tname;
              iname.len = declen;
      } else {
              iname.name = fname->ctext;

fs/ceph/crypto.h +2 -2

index b748e2060bc9..79cb563fd887 100644
@@ -115,7 +115,7 @@ static inline void ceph_fname_free_buffer(struct inode *parent,
              fscrypt_fname_free_buffer(fname);
 }
 
-int ceph_fname_to_usr(const struct ceph_fname *fname, struct fscrypt_str *tname,
+int ceph_fname_to_usr(const struct ceph_fname *fname, unsigned char *tname,
                    struct fscrypt_str *oname, bool *is_nokey);
 int ceph_fscrypt_prepare_readdir(struct inode *dir);
 

@@ -204,7 +204,7 @@ static inline void ceph_fname_free_buffer(struct inode *parent,
 }
 
 static inline int ceph_fname_to_usr(const struct ceph_fname *fname,
-                                 struct fscrypt_str *tname,
+                                 unsigned char *tname,
                                  struct fscrypt_str *oname, bool *is_nokey)
 {
      oname->name = fname->name;

fs/ceph/mds_client.c +3 -3

index ed17e0023705..aa6730b48e97 100644
@@ -488,11 +488,11 @@ static int parse_reply_info_readdir(void **p, void *end,
              struct inode *inode = d_inode(req->r_dentry);
              struct ceph_inode_info *ci = ceph_inode(inode);
              struct ceph_mds_reply_dir_entry *rde = info->dir_entries + i;
-             struct fscrypt_str tname = FSTR_INIT(NULL, 0);
              struct fscrypt_str oname = FSTR_INIT(NULL, 0);
              struct ceph_fname fname;
              u32 altname_len, _name_len;
              u8 *altname, *_name;
+             u8 *tname = NULL;
 
              /* dentry */
              ceph_decode_32_safe(p, end, _name_len, bad);

@@ -540,7 +540,7 @@ static int parse_reply_info_readdir(void **p, void *end,
                       * always be shorter, which is 3/4 of origin
                       * string.
                       */
-                     tname.name = _name;
+                     tname = _name;
 
                      /*
                       * Set oname to _name too, and this will be

@@ -557,7 +557,7 @@ static int parse_reply_info_readdir(void **p, void *end,
                      oname.len = altname_len;
              }
              rde->is_nokey = false;
-             err = ceph_fname_to_usr(&fname, &tname, &oname, &rde->is_nokey);
+             err = ceph_fname_to_usr(&fname, tname, &oname, &rde->is_nokey);
              if (err) {
                      pr_err_client(cl, "unable to decode %.*s, got %d\n",
                                    _name_len, _name, err);

Quoted 29 lines · David Laight

Quoted 25 lines · On Tue, 26 May 2026 19:58:27 -0700 Sam Edwards <[email protected]> wrote:

ceph_fname_to_usr() needs a temporary buffer for some operations (currently only base64-decoding ciphertext) and it is convenient to allow the caller to specify this buffer to avoid a heap allocation, so it has a (nullable) tname argument. Until now, this argument was a struct fscrypt_str; however, this is unnecessary for two reasons:

1. tname->len isn't used anywhere: ceph_fname_to_usr() assumes a buffer large enough to hold the ciphertext, and parse_reply_info_readdir() -- the only caller to use tname -- doesn't set it.
2. While the tname parameter is documented "may be NULL," parse_reply_info_readdir() always passes it but with tname->name sometimes NULL in violation of the contract, indicating that the unnecessary container creates actual confusion.

Therefore, change the type to unsigned char * and pass the buffer directly.

Signed-off-by Sam Edwards <[email protected]>

---
 fs/ceph/crypto.c     | 10 +++++-----
 fs/ceph/crypto.h     |  4 ++--
 fs/ceph/mds_client.c |  6 +++---
 3 files changed, 10 insertions(+), 10 deletions(-)

Quoted 14 lines

fs/ceph/crypto.c int ceph_encode_encrypted_dname(struct inode *parent, char *buf, int elen) · line 303

Quoted 10 lines

fs/ceph/crypto.c +1 -1

index 64d240759277..7515cb251226 100644
@@ -300,7 +300,7 @@ int ceph_encode_encrypted_dname(struct inode *parent, char *buf, int elen)
  *
  * Returns 0 on success or negative error code on error.
  */
-int ceph_fname_to_usr(const struct ceph_fname *fname, struct fscrypt_str *tname,
+int ceph_fname_to_usr(const struct ceph_fname *fname, unsigned char *tname,  

I can't help feeling that the buffer length should also be passed. Either explicitly or, if constant, implicitly by embedding the array in a structure.

It isn't constant; the specific requirement (unchanged in patch 2) is that the buffer be at least large enough to hold the ciphertext. The only caller to pass tname has a comment explaining how it meets the size requirement, so this is currently safe.

Or is your feeling more about general robustness, ensuring that the function prototype of ceph_fname_to_usr() makes it hard for future patches to ignore the length requirement? If so, the issue is ultimately that the base64_*() functions don't accept a dstlen that ceph_fname_to_usr() could use to (meaningfully) enforce the size requirement.

Cheers,
Sam

Quoted 86 lines

-- David

Quoted 81 lines

fs/ceph/crypto.c +4 -4

                    struct fscrypt_str *oname, bool *is_nokey)
 {
      struct inode *dir = fname->dir;

@@ -357,16 +357,16 @@ int ceph_fname_to_usr(const struct ceph_fname *fname, struct fscrypt_str *tname,
                      ret = fscrypt_fname_alloc_buffer(NAME_MAX, &_tname);
                      if (ret)
                              goto out_inode;
-                     tname = &_tname;
+                     tname = _tname.name;
              }
 
-             declen = base64_decode(name, name_len,
-                                    tname->name, false, BASE64_IMAP);
+             declen = base64_decode(name, name_len, tname, false,
+                                    BASE64_IMAP);
              if (declen <= 0) {
                      ret = -EIO;
                      goto out;
              }
-             iname.name = tname->name;
+             iname.name = tname;
              iname.len = declen;
      } else {
              iname.name = fname->ctext;

fs/ceph/crypto.h +2 -2

index b748e2060bc9..79cb563fd887 100644
@@ -115,7 +115,7 @@ static inline void ceph_fname_free_buffer(struct inode *parent,
              fscrypt_fname_free_buffer(fname);
 }
 
-int ceph_fname_to_usr(const struct ceph_fname *fname, struct fscrypt_str *tname,
+int ceph_fname_to_usr(const struct ceph_fname *fname, unsigned char *tname,
                    struct fscrypt_str *oname, bool *is_nokey);
 int ceph_fscrypt_prepare_readdir(struct inode *dir);
 

@@ -204,7 +204,7 @@ static inline void ceph_fname_free_buffer(struct inode *parent,
 }
 
 static inline int ceph_fname_to_usr(const struct ceph_fname *fname,
-                                 struct fscrypt_str *tname,
+                                 unsigned char *tname,
                                  struct fscrypt_str *oname, bool *is_nokey)
 {
      oname->name = fname->name;

fs/ceph/mds_client.c +3 -3

index ed17e0023705..aa6730b48e97 100644
@@ -488,11 +488,11 @@ static int parse_reply_info_readdir(void **p, void *end,
              struct inode *inode = d_inode(req->r_dentry);
              struct ceph_inode_info *ci = ceph_inode(inode);
              struct ceph_mds_reply_dir_entry *rde = info->dir_entries + i;
-             struct fscrypt_str tname = FSTR_INIT(NULL, 0);
              struct fscrypt_str oname = FSTR_INIT(NULL, 0);
              struct ceph_fname fname;
              u32 altname_len, _name_len;
              u8 *altname, *_name;
+             u8 *tname = NULL;
 
              /* dentry */
              ceph_decode_32_safe(p, end, _name_len, bad);

@@ -540,7 +540,7 @@ static int parse_reply_info_readdir(void **p, void *end,
                       * always be shorter, which is 3/4 of origin
                       * string.
                       */
-                     tname.name = _name;
+                     tname = _name;
 
                      /*
                       * Set oname to _name too, and this will be

@@ -557,7 +557,7 @@ static int parse_reply_info_readdir(void **p, void *end,
                      oname.len = altname_len;
              }
              rde->is_nokey = false;
-             err = ceph_fname_to_usr(&fname, &tname, &oname, &rde->is_nokey);
+             err = ceph_fname_to_usr(&fname, tname, &oname, &rde->is_nokey);
              if (err) {
                      pr_err_client(cl, "unable to decode %.*s, got %d\n",
                                    _name_len, _name, err);  

Quoted 46 lines · On Wed, 27 May 2026 11:06:08 -0700 Sam Edwards <[email protected]> wrote:

Quoted 29 lines · David Laight

Quoted 25 lines · On Tue, 26 May 2026 19:58:27 -0700 Sam Edwards <[email protected]> wrote:

ceph_fname_to_usr() needs a temporary buffer for some operations (currently only base64-decoding ciphertext) and it is convenient to allow the caller to specify this buffer to avoid a heap allocation, so it has a (nullable) tname argument. Until now, this argument was a struct fscrypt_str; however, this is unnecessary for two reasons:

1. tname->len isn't used anywhere: ceph_fname_to_usr() assumes a buffer large enough to hold the ciphertext, and parse_reply_info_readdir() -- the only caller to use tname -- doesn't set it.
2. While the tname parameter is documented "may be NULL," parse_reply_info_readdir() always passes it but with tname->name sometimes NULL in violation of the contract, indicating that the unnecessary container creates actual confusion.

Therefore, change the type to unsigned char * and pass the buffer directly.

Signed-off-by Sam Edwards <[email protected]>

---
 fs/ceph/crypto.c     | 10 +++++-----
 fs/ceph/crypto.h     |  4 ++--
 fs/ceph/mds_client.c |  6 +++---
 3 files changed, 10 insertions(+), 10 deletions(-)

Quoted 14 lines

fs/ceph/crypto.c int ceph_encode_encrypted_dname(struct inode *parent, char *buf, int elen) · line 303

Quoted 10 lines

fs/ceph/crypto.c +1 -1

index 64d240759277..7515cb251226 100644
@@ -300,7 +300,7 @@ int ceph_encode_encrypted_dname(struct inode *parent, char *buf, int elen)
  *
  * Returns 0 on success or negative error code on error.
  */
-int ceph_fname_to_usr(const struct ceph_fname *fname, struct fscrypt_str *tname,
+int ceph_fname_to_usr(const struct ceph_fname *fname, unsigned char *tname,

I can't help feeling that the buffer length should also be passed. Either explicitly or, if constant, implicitly by embedding the array in a structure.

Quoted 4 lines

It isn't constant; the specific requirement (unchanged in patch 2) is that the buffer be at least large enough to hold the ciphertext. The only caller to pass tname has a comment explaining how it meets the size requirement, so this is currently safe.

Ugg...
That is just an accident waiting to happen.

Quoted 6 lines

Or is your feeling more about general robustness, ensuring that the function prototype of ceph_fname_to_usr() makes it hard for future patches to ignore the length requirement? If so, the issue is ultimately that the base64_*() functions don't accept a dstlen that ceph_fname_to_usr() could use to (meaningfully) enforce the size requirement.

The output for the base64 functions depends only on the size of the input - so is easy to get right.
And for decode is always shorter.

I've just looked at what happens when tname is NULL - that looks broken as well - why not just kmalloc() a buffer that is the right size instead of using a wrapper function that might return a different length entirely.
Maybe it should be too long, but bugs happen.

There are seem to be random overwrites of buffers of pointers to buffers - more code that is badly fragile.

-- David

Quoted 90 lines

Cheers,
Sam

Quoted 86 lines

-- David

Quoted 81 lines

fs/ceph/crypto.c +4 -4

                    struct fscrypt_str *oname, bool *is_nokey)
 {
      struct inode *dir = fname->dir;

@@ -357,16 +357,16 @@ int ceph_fname_to_usr(const struct ceph_fname *fname, struct fscrypt_str *tname,
                      ret = fscrypt_fname_alloc_buffer(NAME_MAX, &_tname);
                      if (ret)
                              goto out_inode;
-                     tname = &_tname;
+                     tname = _tname.name;
              }
 
-             declen = base64_decode(name, name_len,
-                                    tname->name, false, BASE64_IMAP);
+             declen = base64_decode(name, name_len, tname, false,
+                                    BASE64_IMAP);
              if (declen <= 0) {
                      ret = -EIO;
                      goto out;
              }
-             iname.name = tname->name;
+             iname.name = tname;
              iname.len = declen;
      } else {
              iname.name = fname->ctext;

fs/ceph/crypto.h +2 -2

index b748e2060bc9..79cb563fd887 100644
@@ -115,7 +115,7 @@ static inline void ceph_fname_free_buffer(struct inode *parent,
              fscrypt_fname_free_buffer(fname);
 }
 
-int ceph_fname_to_usr(const struct ceph_fname *fname, struct fscrypt_str *tname,
+int ceph_fname_to_usr(const struct ceph_fname *fname, unsigned char *tname,
                    struct fscrypt_str *oname, bool *is_nokey);
 int ceph_fscrypt_prepare_readdir(struct inode *dir);
 

@@ -204,7 +204,7 @@ static inline void ceph_fname_free_buffer(struct inode *parent,
 }
 
 static inline int ceph_fname_to_usr(const struct ceph_fname *fname,
-                                 struct fscrypt_str *tname,
+                                 unsigned char *tname,
                                  struct fscrypt_str *oname, bool *is_nokey)
 {
      oname->name = fname->name;

fs/ceph/mds_client.c +3 -3

index ed17e0023705..aa6730b48e97 100644
@@ -488,11 +488,11 @@ static int parse_reply_info_readdir(void **p, void *end,
              struct inode *inode = d_inode(req->r_dentry);
              struct ceph_inode_info *ci = ceph_inode(inode);
              struct ceph_mds_reply_dir_entry *rde = info->dir_entries + i;
-             struct fscrypt_str tname = FSTR_INIT(NULL, 0);
              struct fscrypt_str oname = FSTR_INIT(NULL, 0);
              struct ceph_fname fname;
              u32 altname_len, _name_len;
              u8 *altname, *_name;
+             u8 *tname = NULL;
 
              /* dentry */
              ceph_decode_32_safe(p, end, _name_len, bad);

@@ -540,7 +540,7 @@ static int parse_reply_info_readdir(void **p, void *end,
                       * always be shorter, which is 3/4 of origin
                       * string.
                       */
-                     tname.name = _name;
+                     tname = _name;
 
                      /*
                       * Set oname to _name too, and this will be

@@ -557,7 +557,7 @@ static int parse_reply_info_readdir(void **p, void *end,
                      oname.len = altname_len;
              }
              rde->is_nokey = false;
-             err = ceph_fname_to_usr(&fname, &tname, &oname, &rde->is_nokey);
+             err = ceph_fname_to_usr(&fname, tname, &oname, &rde->is_nokey);
              if (err) {
                      pr_err_client(cl, "unable to decode %.*s, got %d\n",
                                    _name_len, _name, err);

The fscrypt subsystem uses the scatterlist crypto API, inheriting its requirement that any buffers are in the linear mapping region. However, the messenger client uses kvmalloc() to create buffers for messages, which will occasionally place those buffers in the vmalloc() region when physical memory fragmentation doesn't permit a large enough kmalloc(). The various callers of ceph_fname_to_usr() directly pass (slices of) raw messages from the MDS without considering that the messages may be in vmalloc() buffers, resulting in oopses especially on non-x86 platforms (see 'Closes:' for more details and a reproducer).

Make ceph_fname_to_usr() explicitly tolerant of vmalloc()-allocated fname->ctext, fname->name, and/or oname->name buffers, using tname (which, when non-null, must be a linear address; when null, is briefly allocated as necessary) as a bounce buffer to avoid passing any inappropriate addresses to fscrypt_fname_disk_to_usr().

Additionally change parse_reply_info_readdir() -- the only function to supply its own tname -- to follow the new "tname must never come from vmalloc()" rule by passing NULL when the message is not in the linear region. Though this causes a per-dentry kmalloc()+kfree(), this overhead exists only when processing the minority of messages that spill into vmalloc(). My (crude) testing puts this at only about 1 in 8,000 readdir messages. Still, if the overhead proves unreasonable in the future, it is easy enough to mitigate: a future change could allocate a bounce buffer in parse_reply_info_readdir() and use that as tname instead.

Fixes 457117f077c67 ("ceph: add helpers for converting names for userland presentation")

Closes https://urldefense.proofpoint.com/v2/url?u=https-3A__lore.kernel.org_ceph-2Ddevel_CAH5Ym4ga7miUQE0K-2DcJA93Ya7w62P69MAN27R5cBiYnudoOHdA-40mail.gmail.com_T_&d=DwIDAg&c=BSDicqBQBDjDI9RkVyTcHQ&r=q5bIm4AXMzc8NJu1_RGmnQ2fMWKq4Y4RAkElvUgSs00&m=bcX0FhBD6jzWXGOsw2LoJOl_TqgobmwNBmqNIhj2K0qBn2krB8IUrIhcUs8LmJWM&s=2uInY5Ys7xQ_57Ifo4uovP7_e8SN0Q_wnzBDX-uj0hE&e=

Cc [email protected] # v6.6+

Signed-off-by Sam Edwards <[email protected]>

---
 fs/ceph/crypto.c     | 37 +++++++++++++++++++++++++++++--------
 fs/ceph/mds_client.c |  8 ++++++--
 2 files changed, 35 insertions(+), 10 deletions(-)

fs/ceph/crypto.c +27 -8

index 7515cb251226..61d6830d16bc 100644
@@ -298,6 +298,10 @@ int ceph_encode_encrypted_dname(struct inode *parent, char *buf, int elen)
  * Otherwise, base64 decode the string, and then ask fscrypt to format it
  * for userland presentation.
  *
+ * Though the fscrypt/crypto subsystems broadly expect all buffers to be in the
+ * linear-mapped region, this function slightly relaxes those requirements:
+ * fname->ctext, fname->name, and oname->name may be vmalloc(), but not tname.
+ *
  * Returns 0 on success or negative error code on error.
  */
 int ceph_fname_to_usr(const struct ceph_fname *fname, unsigned char *tname,

@@ -305,11 +309,15 @@ int ceph_fname_to_usr(const struct ceph_fname *fname, unsigned char *tname,
 {
 	struct inode *dir = fname->dir;
 	struct fscrypt_str _tname = FSTR_INIT(NULL, 0);
+	struct fscrypt_str _oname;
 	struct fscrypt_str iname;
 	char *name = fname->name;
 	int name_len = fname->name_len;
 	int ret;
 
+	if (WARN_ON_ONCE(tname && is_vmalloc_addr(tname)))
+		return -EIO;
+
 	/* Sanity check that the resulting name will fit in the buffer */
 	if (fname->name_len > NAME_MAX || fname->ctext_len > NAME_MAX)
 		return -EIO;

@@ -350,16 +358,18 @@ int ceph_fname_to_usr(const struct ceph_fname *fname, unsigned char *tname,
 		goto out_inode;
 	}
 
+	if (!tname && (fname->ctext_len == 0 ||
+		       unlikely(is_vmalloc_addr(fname->ctext)) ||
+		       unlikely(is_vmalloc_addr(oname->name)))) {
+		ret = fscrypt_fname_alloc_buffer(NAME_MAX, &_tname);
+		if (ret)
+			goto out_inode;
+		tname = _tname.name;
+	}
+
 	if (fname->ctext_len == 0) {
 		int declen;
 
-		if (!tname) {
-			ret = fscrypt_fname_alloc_buffer(NAME_MAX, &_tname);
-			if (ret)
-				goto out_inode;
-			tname = _tname.name;
-		}
-
 		declen = base64_decode(name, name_len, tname, false,
 				       BASE64_IMAP);
 		if (declen <= 0) {

@@ -368,12 +378,21 @@ int ceph_fname_to_usr(const struct ceph_fname *fname, unsigned char *tname,
 		}
 		iname.name = tname;
 		iname.len = declen;
+	} else if (unlikely(is_vmalloc_addr(fname->ctext))) {
+		memcpy(tname, fname->ctext, fname->ctext_len);
+
+		iname.name = tname;
+		iname.len = fname->ctext_len;
 	} else {
 		iname.name = fname->ctext;
 		iname.len = fname->ctext_len;
 	}
 
-	ret = fscrypt_fname_disk_to_usr(dir, 0, 0, &iname, oname);
+	_oname.name = unlikely(is_vmalloc_addr(oname->name)) ?
+		tname : oname->name;
+	_oname.len = oname->len;
+	ret = fscrypt_fname_disk_to_usr(dir, 0, 0, &iname, &_oname);
+	oname->len = _oname.len;
 	if (!ret && (dir != fname->dir)) {
 		char tmp_buf[BASE64_CHARS(NAME_MAX)];
 

fs/ceph/crypto.c +0 -0

 out:

fs/ceph/mds_client.c +6 -2

index aa6730b48e97..8fcf185e3a82 100644
@@ -538,9 +538,13 @@ static int parse_reply_info_readdir(void **p, void *end,
 			 * to do the base64_decode in-place. It's
 			 * safe because the decoded string should
 			 * always be shorter, which is 3/4 of origin
-			 * string.
+			 * string. If this message was allocated with
+			 * vmalloc() (happens, but rarely), leave it
+			 * NULL and let ceph_fname_to_usr() allocate
+			 * suitable temporary working space instead.
 			 */
-			tname = _name;
+			if (likely(!is_vmalloc_addr(_name)))
+				tname = _name;
 
 			/*
 			 * Set oname to _name too, and this will be

Quoted 116 lines · Sam Edwards

The fscrypt subsystem uses the scatterlist crypto API, inheriting its requirement that any buffers are in the linear mapping region. However, the messenger client uses kvmalloc() to create buffers for messages, which will occasionally place those buffers in the vmalloc() region when physical memory fragmentation doesn't permit a large enough kmalloc(). The various callers of ceph_fname_to_usr() directly pass (slices of) raw messages from the MDS without considering that the messages may be in vmalloc() buffers, resulting in oopses especially on non-x86 platforms (see 'Closes:' for more details and a reproducer).

Make ceph_fname_to_usr() explicitly tolerant of vmalloc()-allocated fname->ctext, fname->name, and/or oname->name buffers, using tname (which, when non-null, must be a linear address; when null, is briefly allocated as necessary) as a bounce buffer to avoid passing any inappropriate addresses to fscrypt_fname_disk_to_usr().

Additionally change parse_reply_info_readdir() -- the only function to supply its own tname -- to follow the new "tname must never come from vmalloc()" rule by passing NULL when the message is not in the linear region. Though this causes a per-dentry kmalloc()+kfree(), this overhead exists only when processing the minority of messages that spill into vmalloc(). My (crude) testing puts this at only about 1 in 8,000 readdir messages. Still, if the overhead proves unreasonable in the future, it is easy enough to mitigate: a future change could allocate a bounce buffer in parse_reply_info_readdir() and use that as tname instead.

Fixes 457117f077c67 ("ceph: add helpers for converting names for userland presentation")

Closes https://urldefense.proofpoint.com/v2/url?u=https-3A__lore.kernel.org_ceph-2Ddevel_CAH5Ym4ga7miUQE0K-2DcJA93Ya7w62P69MAN27R5cBiYnudoOHdA-40mail.gmail.com_T_&d=DwIDAg&c=BSDicqBQBDjDI9RkVyTcHQ&r=q5bIm4AXMzc8NJu1_RGmnQ2fMWKq4Y4RAkElvUgSs00&m=bcX0FhBD6jzWXGOsw2LoJOl_TqgobmwNBmqNIhj2K0qBn2krB8IUrIhcUs8LmJWM&s=2uInY5Ys7xQ_57Ifo4uovP7_e8SN0Q_wnzBDX-uj0hE&e=

Cc [email protected] # v6.6+

Signed-off-by Sam Edwards <[email protected]>

---
 fs/ceph/crypto.c     | 37 +++++++++++++++++++++++++++++--------
 fs/ceph/mds_client.c |  8 ++++++--
 2 files changed, 35 insertions(+), 10 deletions(-)

fs/ceph/crypto.c +27 -8

index 7515cb251226..61d6830d16bc 100644
@@ -298,6 +298,10 @@ int ceph_encode_encrypted_dname(struct inode *parent, char *buf, int elen)
  * Otherwise, base64 decode the string, and then ask fscrypt to format it
  * for userland presentation.
  *
+ * Though the fscrypt/crypto subsystems broadly expect all buffers to be in the
+ * linear-mapped region, this function slightly relaxes those requirements:
+ * fname->ctext, fname->name, and oname->name may be vmalloc(), but not tname.
+ *
  * Returns 0 on success or negative error code on error.
  */
 int ceph_fname_to_usr(const struct ceph_fname *fname, unsigned char *tname,

@@ -305,11 +309,15 @@ int ceph_fname_to_usr(const struct ceph_fname *fname, unsigned char *tname,
 {
      struct inode *dir = fname->dir;
      struct fscrypt_str _tname = FSTR_INIT(NULL, 0);
+     struct fscrypt_str _oname;
      struct fscrypt_str iname;
      char *name = fname->name;
      int name_len = fname->name_len;
      int ret;
 
+     if (WARN_ON_ONCE(tname && is_vmalloc_addr(tname)))
+             return -EIO;
+
      /* Sanity check that the resulting name will fit in the buffer */
      if (fname->name_len > NAME_MAX || fname->ctext_len > NAME_MAX)
              return -EIO;

@@ -350,16 +358,18 @@ int ceph_fname_to_usr(const struct ceph_fname *fname, unsigned char *tname,
              goto out_inode;
      }
 
+     if (!tname && (fname->ctext_len == 0 ||
+                    unlikely(is_vmalloc_addr(fname->ctext)) ||
+                    unlikely(is_vmalloc_addr(oname->name)))) {
+             ret = fscrypt_fname_alloc_buffer(NAME_MAX, &_tname);
+             if (ret)
+                     goto out_inode;
+             tname = _tname.name;
+     }
+
      if (fname->ctext_len == 0) {
              int declen;
 
-             if (!tname) {
-                     ret = fscrypt_fname_alloc_buffer(NAME_MAX, &_tname);
-                     if (ret)
-                             goto out_inode;
-                     tname = _tname.name;
-             }
-
              declen = base64_decode(name, name_len, tname, false,
                                     BASE64_IMAP);
              if (declen <= 0) {

@@ -368,12 +378,21 @@ int ceph_fname_to_usr(const struct ceph_fname *fname, unsigned char *tname,
              }
              iname.name = tname;
              iname.len = declen;
+     } else if (unlikely(is_vmalloc_addr(fname->ctext))) {
+             memcpy(tname, fname->ctext, fname->ctext_len);
+
+             iname.name = tname;
+             iname.len = fname->ctext_len;
      } else {
              iname.name = fname->ctext;
              iname.len = fname->ctext_len;
      }
 
-     ret = fscrypt_fname_disk_to_usr(dir, 0, 0, &iname, oname);
+     _oname.name = unlikely(is_vmalloc_addr(oname->name)) ?
+             tname : oname->name;
+     _oname.len = oname->len;
+     ret = fscrypt_fname_disk_to_usr(dir, 0, 0, &iname, &_oname);
+     oname->len = _oname.len;
      if (!ret && (dir != fname->dir)) {
              char tmp_buf[BASE64_CHARS(NAME_MAX)];
 

fs/ceph/crypto.c int ceph_fname_to_usr(const struct ceph_fname *fname, unsigned char *tname, · line 405

Quoted 6 lines

fs/ceph/crypto.c +2 -0

@@ -381,6 +400,8 @@ int ceph_fname_to_usr(const struct ceph_fname *fname, unsigned char *tname,
                                  oname->len, oname->name, dir->i_ino);
              memcpy(oname->name, tmp_buf, name_len);
              oname->len = name_len;
+     } else if (!ret && unlikely(is_vmalloc_addr(oname->name))) {
+             memcpy(oname->name, _oname.name, _oname.len);
      }

When both dir != fname->dir (longname snapshot) and is_vmalloc_addr(oname->name) are true:

(1) The if branch is taken — NOT the else if.
(2) _oname.name = tname holds the decrypted result (fscrypt wrote there).
(3) oname->name is the stale vmalloc buffer — the copy-back in the else if was never executed.
(4) The snprintf reads oname->name and formats a snapshot name from garbage.

Am I right?

This part of logic needs to be reworked carefully. This if - else construction becomes really complicated to understand.

Thanks,
Slava.

Quoted 22 lines

fs/ceph/crypto.c +0 -0

 out:

fs/ceph/mds_client.c +6 -2

index aa6730b48e97..8fcf185e3a82 100644
@@ -538,9 +538,13 @@ static int parse_reply_info_readdir(void **p, void *end,
                       * to do the base64_decode in-place. It's
                       * safe because the decoded string should
                       * always be shorter, which is 3/4 of origin
-                      * string.
+                      * string. If this message was allocated with
+                      * vmalloc() (happens, but rarely), leave it
+                      * NULL and let ceph_fname_to_usr() allocate
+                      * suitable temporary working space instead.
                       */
-                     tname = _name;
+                     if (likely(!is_vmalloc_addr(_name)))
+                             tname = _name;
 
                      /*
                       * Set oname to _name too, and this will be