Allow deleting files with unsupported encryption policy

PATCH In review Eric Biggers 1 participant 11 messages Dec 3, 2020 – Dec 6, 2020

Subsystems (6)

VFS Memory technology devices (MTD) ext4 file system F2FS file system +2 more subsystems

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Eric Biggers

author maintainer

2020-12-03 02:23 UTC #0 lore raw

v2 cover Allow deleting files with unsupported encryption policy

Currently it's impossible to delete files that use an unsupported encryption policy, as the kernel will just return an error when performing any operation on the top-level encrypted directory, even just a path lookup into the directory or opening the directory for readdir.

It's desirable to return errors for most operations on files that use an unsupported encryption policy, but the current behavior is too strict. We need to allow enough to delete files, so that people can't be stuck with undeletable files when downgrading kernel versions. That includes allowing directories to be listed and allowing dentries to be looked up.

This series fixes this (on ext4, f2fs, and ubifs) by treating an unsupported encryption policy in the same way as "key unavailable" in the cases that are required for a recursive delete to work.

The actual fix is in patch 9, so see that for more details.

Patches 1-8 are cleanups that prepare for the actual fix by removing direct use of fscrypt_get_encryption_info() by filesystems.

This patchset applies to branch "master" (commit 4a4b8721f1a5) of
https://git.kernel.org/pub/scm/fs/fscrypt/fscrypt.git.

Changed since v1:
- Made some minor updates to commit messages.
- Added Reviewed-by tags.

Eric Biggers (9):
ext4: remove ext4_dir_open()
f2fs: remove f2fs_dir_open()
ubifs: remove ubifs_dir_open()
ext4: don't call fscrypt_get_encryption_info() from dx_show_leaf()
fscrypt: introduce fscrypt_prepare_readdir()
fscrypt: move body of fscrypt_prepare_setattr() out-of-line
fscrypt: move fscrypt_require_key() to fscrypt_private.h
fscrypt: unexport fscrypt_get_encryption_info()
fscrypt: allow deleting files with unsupported encryption policy

 fs/crypto/fname.c           |  8 +++-
 fs/crypto/fscrypt_private.h | 28 ++++++++++++++
 fs/crypto/hooks.c           | 16 +++++++-
 fs/crypto/keysetup.c        | 20 ++++++++--
 fs/crypto/policy.c          | 22 +++++++----
 fs/ext4/dir.c               | 16 ++------
 fs/ext4/namei.c             | 10 +----
 fs/f2fs/dir.c               | 10 +----
 fs/ubifs/dir.c              | 11 +-----
 include/linux/fscrypt.h     | 75 +++++++++++++++++++------------------
 10 files changed, 126 insertions(+), 90 deletions(-)

base-commit: 4a4b8721f1a5e4b01e45b3153c68d5a1014b25de

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Eric Biggers

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2020-12-03 02:23 UTC #1 lore raw

PATCH v2 1/9 ext4: remove ext4_dir_open()

From: Eric Biggers <[email protected]>

Since encrypted directories can be opened and searched without their key being available, and each readdir and ->lookup() tries to set up the key, trying to set up the key in ->open() too isn't really useful.

Just remove it so that directories don't need an ->open() method anymore, and so that we eliminate a use of fscrypt_get_encryption_info() (which I'd like to stop exporting to filesystems).

Reviewed-by Andreas Dilger <[email protected]>

Signed-off-by Eric Biggers <[email protected]>

---
 fs/ext4/dir.c | 8 --------
 1 file changed, 8 deletions(-)

fs/ext4/dir.c +0 -8

index ca50c90adc4c4..16bfbdd5007c7 100644
@@ -616,13 +616,6 @@ static int ext4_dx_readdir(struct file *file, struct dir_context *ctx)
 	return 0;
 }
 
-static int ext4_dir_open(struct inode * inode, struct file * filp)
-{
-	if (IS_ENCRYPTED(inode))
-		return fscrypt_get_encryption_info(inode) ? -EACCES : 0;
-	return 0;
-}
-
 static int ext4_release_dir(struct inode *inode, struct file *filp)
 {
 	if (filp->private_data)

@@ -664,7 +657,6 @@ const struct file_operations ext4_dir_operations = {
 	.compat_ioctl	= ext4_compat_ioctl,
 #endif
 	.fsync		= ext4_sync_file,
-	.open		= ext4_dir_open,
 	.release	= ext4_release_dir,
 };

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Eric Biggers

author maintainer

2020-12-03 02:23 UTC #2 lore raw

PATCH v2 2/9 f2fs: remove f2fs_dir_open()

In reply to Eric Biggers

From: Eric Biggers <[email protected]>

Just remove it so that directories don't need an ->open() method anymore, and so that we eliminate a use of fscrypt_get_encryption_info() (which I'd like to stop exporting to filesystems).

Reviewed-by Chao Yu <[email protected]>

Signed-off-by Eric Biggers <[email protected]>

---
 fs/f2fs/dir.c | 8 --------
 1 file changed, 8 deletions(-)

fs/f2fs/dir.c +0 -8

index 4b9ef8bbfa4a9..47bee953fc8d8 100644
@@ -1081,19 +1081,11 @@ static int f2fs_readdir(struct file *file, struct dir_context *ctx)
 	return err < 0 ? err : 0;
 }
 
-static int f2fs_dir_open(struct inode *inode, struct file *filp)
-{
-	if (IS_ENCRYPTED(inode))
-		return fscrypt_get_encryption_info(inode) ? -EACCES : 0;
-	return 0;
-}
-
 const struct file_operations f2fs_dir_operations = {
 	.llseek		= generic_file_llseek,
 	.read		= generic_read_dir,
 	.iterate_shared	= f2fs_readdir,
 	.fsync		= f2fs_sync_file,
-	.open		= f2fs_dir_open,
 	.unlocked_ioctl	= f2fs_ioctl,
 #ifdef CONFIG_COMPAT
 	.compat_ioctl   = f2fs_compat_ioctl,

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Eric Biggers

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2020-12-03 02:23 UTC #3 lore raw

PATCH v2 3/9 ubifs: remove ubifs_dir_open()

In reply to Eric Biggers

From: Eric Biggers <[email protected]>

Just remove it so that directories don't need an ->open() method anymore, and so that we eliminate a use of fscrypt_get_encryption_info() (which I'd like to stop exporting to filesystems).

Signed-off-by Eric Biggers <[email protected]>

---
 fs/ubifs/dir.c | 9 ---------
 1 file changed, 9 deletions(-)

fs/ubifs/dir.c +0 -9

index 08fde777c3247..009fbf844d3e6 100644
@@ -1619,14 +1619,6 @@ int ubifs_getattr(const struct path *path, struct kstat *stat,
 	return 0;
 }
 
-static int ubifs_dir_open(struct inode *dir, struct file *file)
-{
-	if (IS_ENCRYPTED(dir))
-		return fscrypt_get_encryption_info(dir) ? -EACCES : 0;
-
-	return 0;
-}
-
 const struct inode_operations ubifs_dir_inode_operations = {
 	.lookup      = ubifs_lookup,
 	.create      = ubifs_create,

@@ -1653,7 +1645,6 @@ const struct file_operations ubifs_dir_operations = {
 	.iterate_shared = ubifs_readdir,
 	.fsync          = ubifs_fsync,
 	.unlocked_ioctl = ubifs_ioctl,
-	.open		= ubifs_dir_open,
 #ifdef CONFIG_COMPAT
 	.compat_ioctl   = ubifs_compat_ioctl,
 #endif

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Eric Biggers

author maintainer

2020-12-03 02:23 UTC #4 lore raw

PATCH v2 4/9 ext4: don't call fscrypt_get_encryption_info() from dx_show_leaf()

In reply to Eric Biggers

From: Eric Biggers <[email protected]>

The call to fscrypt_get_encryption_info() in dx_show_leaf() is too low in the call tree; fscrypt_get_encryption_info() should have already been called when starting the directory operation. And indeed, it already is. Moreover, the encryption key is guaranteed to already be available because dx_show_leaf() is only called when adding a new directory entry.

And even if the key wasn't available, dx_show_leaf() uses fscrypt_fname_disk_to_usr() which knows how to create a no-key name.

So for the above reasons, and because it would be desirable to stop exporting fscrypt_get_encryption_info() directly to filesystems, remove the call to fscrypt_get_encryption_info() from dx_show_leaf().

Reviewed-by Andreas Dilger <[email protected]>

Signed-off-by Eric Biggers <[email protected]>

---
 fs/ext4/namei.c | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

fs/ext4/namei.c +1 -7

index 793fc7db9d28f..7b31aea3e0253 100644
@@ -643,13 +643,7 @@ static struct stats dx_show_leaf(struct inode *dir,
 
 				name  = de->name;
 				len = de->name_len;
-				if (IS_ENCRYPTED(dir))
-					res = fscrypt_get_encryption_info(dir);
-				if (res) {
-					printk(KERN_WARNING "Error setting up"
-					       " fname crypto: %d\n", res);
-				}
-				if (!fscrypt_has_encryption_key(dir)) {
+				if (!IS_ENCRYPTED(dir)) {
 					/* Directory is not encrypted */
 					ext4fs_dirhash(dir, de->name,
 						de->name_len, &h);

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Eric Biggers

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2020-12-03 02:23 UTC #5 lore raw

PATCH v2 5/9 fscrypt: introduce fscrypt_prepare_readdir()

In reply to Eric Biggers

From: Eric Biggers <[email protected]>

The last remaining use of fscrypt_get_encryption_info() from filesystems is for readdir (->iterate_shared()). Every other call is now in fs/crypto/ as part of some other higher-level operation.

We need to add a new argument to fscrypt_get_encryption_info() to indicate whether the encryption policy is allowed to be unrecognized or not. Doing this is easier if we can work with high-level operations rather than direct filesystem use of fscrypt_get_encryption_info().

So add a function fscrypt_prepare_readdir() which wraps the call to fscrypt_get_encryption_info() for the readdir use case.

Reviewed-by Andreas Dilger <[email protected]>

Signed-off-by Eric Biggers <[email protected]>

---
 fs/crypto/hooks.c       |  6 ++++++
 fs/ext4/dir.c           |  8 +++-----
 fs/ext4/namei.c         |  2 +-
 fs/f2fs/dir.c           |  2 +-
 fs/ubifs/dir.c          |  2 +-
 include/linux/fscrypt.h | 24 ++++++++++++++++++++++++
 6 files changed, 36 insertions(+), 8 deletions(-)

fs/crypto/hooks.c +6 -0

index c809a4afa057e..82f351d3113ac 100644
@@ -114,6 +114,12 @@ int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry,
 }
 EXPORT_SYMBOL_GPL(__fscrypt_prepare_lookup);
 
+int __fscrypt_prepare_readdir(struct inode *dir)
+{
+	return fscrypt_get_encryption_info(dir);
+}
+EXPORT_SYMBOL_GPL(__fscrypt_prepare_readdir);
+
 /**
  * fscrypt_prepare_setflags() - prepare to change flags with FS_IOC_SETFLAGS
  * @inode: the inode on which flags are being changed

fs/ext4/dir.c +3 -5

index 16bfbdd5007c7..c6d16353326a9 100644
@@ -118,11 +118,9 @@ static int ext4_readdir(struct file *file, struct dir_context *ctx)
 	struct buffer_head *bh = NULL;
 	struct fscrypt_str fstr = FSTR_INIT(NULL, 0);
 
-	if (IS_ENCRYPTED(inode)) {
-		err = fscrypt_get_encryption_info(inode);
-		if (err)
-			return err;
-	}
+	err = fscrypt_prepare_readdir(inode);
+	if (err)
+		return err;
 
 	if (is_dx_dir(inode)) {
 		err = ext4_dx_readdir(file, ctx);

fs/ext4/namei.c +1 -1

index 7b31aea3e0253..5fa8436cd5fae 100644
@@ -1004,7 +1004,7 @@ static int htree_dirblock_to_tree(struct file *dir_file,
 					   EXT4_DIR_REC_LEN(0));
 	/* Check if the directory is encrypted */
 	if (IS_ENCRYPTED(dir)) {
-		err = fscrypt_get_encryption_info(dir);
+		err = fscrypt_prepare_readdir(dir);
 		if (err < 0) {
 			brelse(bh);
 			return err;

fs/f2fs/dir.c +1 -1

index 47bee953fc8d8..049500f1e764c 100644
@@ -1022,7 +1022,7 @@ static int f2fs_readdir(struct file *file, struct dir_context *ctx)
 	int err = 0;
 
 	if (IS_ENCRYPTED(inode)) {
-		err = fscrypt_get_encryption_info(inode);
+		err = fscrypt_prepare_readdir(inode);
 		if (err)
 			goto out;

fs/ubifs/dir.c +1 -1

index 009fbf844d3e6..1f33a5598b93f 100644
@@ -514,7 +514,7 @@ static int ubifs_readdir(struct file *file, struct dir_context *ctx)
 		return 0;
 
 	if (encrypted) {
-		err = fscrypt_get_encryption_info(dir);
+		err = fscrypt_prepare_readdir(dir);
 		if (err)
 			return err;

include/linux/fscrypt.h +24 -0

index 0c9e64969b736..8cbb26f556952 100644
@@ -242,6 +242,7 @@ int __fscrypt_prepare_rename(struct inode *old_dir, struct dentry *old_dentry,
 			     unsigned int flags);
 int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry,
 			     struct fscrypt_name *fname);
+int __fscrypt_prepare_readdir(struct inode *dir);
 int fscrypt_prepare_setflags(struct inode *inode,
 			     unsigned int oldflags, unsigned int flags);
 int fscrypt_prepare_symlink(struct inode *dir, const char *target,

@@ -537,6 +538,11 @@ static inline int __fscrypt_prepare_lookup(struct inode *dir,
 	return -EOPNOTSUPP;
 }
 
+static inline int __fscrypt_prepare_readdir(struct inode *dir)
+{
+	return -EOPNOTSUPP;
+}
+
 static inline int fscrypt_prepare_setflags(struct inode *inode,
 					   unsigned int oldflags,
 					   unsigned int flags)

@@ -795,6 +801,24 @@ static inline int fscrypt_prepare_lookup(struct inode *dir,
 	return 0;
 }
 
+/**
+ * fscrypt_prepare_readdir() - prepare to read a possibly-encrypted directory
+ * @dir: the directory inode
+ *
+ * If the directory is encrypted and it doesn't already have its encryption key
+ * set up, try to set it up so that the filenames will be listed in plaintext
+ * form rather than in no-key form.
+ *
+ * Return: 0 on success; -errno on error.  Note that the encryption key being
+ *	   unavailable is not considered an error.
+ */
+static inline int fscrypt_prepare_readdir(struct inode *dir)
+{
+	if (IS_ENCRYPTED(dir))
+		return __fscrypt_prepare_readdir(dir);
+	return 0;
+}
+
 /**
  * fscrypt_prepare_setattr() - prepare to change a possibly-encrypted inode's
  *			       attributes

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Eric Biggers

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2020-12-03 02:23 UTC #6 lore raw

PATCH v2 6/9 fscrypt: move body of fscrypt_prepare_setattr() out-of-line

In reply to Eric Biggers

From: Eric Biggers <[email protected]>

In preparation for reducing the visibility of fscrypt_require_key() by moving it to fscrypt_private.h, move the call to it from fscrypt_prepare_setattr() to an out-of-line function.

Reviewed-by Andreas Dilger <[email protected]>

Signed-off-by Eric Biggers <[email protected]>

---
 fs/crypto/hooks.c       |  8 ++++++++
 include/linux/fscrypt.h | 11 +++++++++--
 2 files changed, 17 insertions(+), 2 deletions(-)

fs/crypto/hooks.c +8 -0

index 82f351d3113ac..1c16dba222d95 100644
@@ -120,6 +120,14 @@ int __fscrypt_prepare_readdir(struct inode *dir)
 }
 EXPORT_SYMBOL_GPL(__fscrypt_prepare_readdir);
 
+int __fscrypt_prepare_setattr(struct dentry *dentry, struct iattr *attr)
+{
+	if (attr->ia_valid & ATTR_SIZE)
+		return fscrypt_require_key(d_inode(dentry));
+	return 0;
+}
+EXPORT_SYMBOL_GPL(__fscrypt_prepare_setattr);
+
 /**
  * fscrypt_prepare_setflags() - prepare to change flags with FS_IOC_SETFLAGS
  * @inode: the inode on which flags are being changed

include/linux/fscrypt.h +9 -2

index 8cbb26f556952..b20900bb829fc 100644
@@ -243,6 +243,7 @@ int __fscrypt_prepare_rename(struct inode *old_dir, struct dentry *old_dentry,
 int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry,
 			     struct fscrypt_name *fname);
 int __fscrypt_prepare_readdir(struct inode *dir);
+int __fscrypt_prepare_setattr(struct dentry *dentry, struct iattr *attr);
 int fscrypt_prepare_setflags(struct inode *inode,
 			     unsigned int oldflags, unsigned int flags);
 int fscrypt_prepare_symlink(struct inode *dir, const char *target,

@@ -543,6 +544,12 @@ static inline int __fscrypt_prepare_readdir(struct inode *dir)
 	return -EOPNOTSUPP;
 }
 
+static inline int __fscrypt_prepare_setattr(struct dentry *dentry,
+					    struct iattr *attr)
+{
+	return -EOPNOTSUPP;
+}
+
 static inline int fscrypt_prepare_setflags(struct inode *inode,
 					   unsigned int oldflags,
 					   unsigned int flags)

@@ -840,8 +847,8 @@ static inline int fscrypt_prepare_readdir(struct inode *dir)
 static inline int fscrypt_prepare_setattr(struct dentry *dentry,
 					  struct iattr *attr)
 {
-	if (attr->ia_valid & ATTR_SIZE)
-		return fscrypt_require_key(d_inode(dentry));
+	if (IS_ENCRYPTED(d_inode(dentry)))
+		return __fscrypt_prepare_setattr(dentry, attr);
 	return 0;
 }

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Eric Biggers

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2020-12-03 02:23 UTC #7 lore raw

PATCH v2 7/9 fscrypt: move fscrypt_require_key() to fscrypt_private.h

In reply to Eric Biggers

From: Eric Biggers <[email protected]>

fscrypt_require_key() is now only used by files in fs/crypto/. So reduce its visibility to fscrypt_private.h. This is also a prerequsite for unexporting fscrypt_get_encryption_info().

Reviewed-by Andreas Dilger <[email protected]>

Signed-off-by Eric Biggers <[email protected]>

---
 fs/crypto/fscrypt_private.h | 26 ++++++++++++++++++++++++++
 include/linux/fscrypt.h     | 26 --------------------------
 2 files changed, 26 insertions(+), 26 deletions(-)

fs/crypto/fscrypt_private.h +26 -0

index a61d4dbf0a0b0..16dd55080127a 100644
@@ -571,6 +571,32 @@ int fscrypt_derive_dirhash_key(struct fscrypt_info *ci,
 void fscrypt_hash_inode_number(struct fscrypt_info *ci,
 			       const struct fscrypt_master_key *mk);
 
+/**
+ * fscrypt_require_key() - require an inode's encryption key
+ * @inode: the inode we need the key for
+ *
+ * If the inode is encrypted, set up its encryption key if not already done.
+ * Then require that the key be present and return -ENOKEY otherwise.
+ *
+ * No locks are needed, and the key will live as long as the struct inode --- so
+ * it won't go away from under you.
+ *
+ * Return: 0 on success, -ENOKEY if the key is missing, or another -errno code
+ * if a problem occurred while setting up the encryption key.
+ */
+static inline int fscrypt_require_key(struct inode *inode)
+{
+	if (IS_ENCRYPTED(inode)) {
+		int err = fscrypt_get_encryption_info(inode);
+
+		if (err)
+			return err;
+		if (!fscrypt_has_encryption_key(inode))
+			return -ENOKEY;
+	}
+	return 0;
+}
+
 /* keysetup_v1.c */
 
 void fscrypt_put_direct_key(struct fscrypt_direct_key *dk);

include/linux/fscrypt.h +0 ~~-26~~

index b20900bb829fc..a07610f279266 100644
@@ -688,32 +688,6 @@ static inline bool fscrypt_has_encryption_key(const struct inode *inode)
 	return fscrypt_get_info(inode) != NULL;
 }
 
-/**
- * fscrypt_require_key() - require an inode's encryption key
- * @inode: the inode we need the key for
- *
- * If the inode is encrypted, set up its encryption key if not already done.
- * Then require that the key be present and return -ENOKEY otherwise.
- *
- * No locks are needed, and the key will live as long as the struct inode --- so
- * it won't go away from under you.
- *
- * Return: 0 on success, -ENOKEY if the key is missing, or another -errno code
- * if a problem occurred while setting up the encryption key.
- */
-static inline int fscrypt_require_key(struct inode *inode)
-{
-	if (IS_ENCRYPTED(inode)) {
-		int err = fscrypt_get_encryption_info(inode);
-
-		if (err)
-			return err;
-		if (!fscrypt_has_encryption_key(inode))
-			return -ENOKEY;
-	}
-	return 0;
-}
-
 /**
  * fscrypt_prepare_link() - prepare to link an inode into a possibly-encrypted
  *			    directory

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Eric Biggers

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2020-12-03 02:23 UTC #8 lore raw

PATCH v2 8/9 fscrypt: unexport fscrypt_get_encryption_info()

In reply to Eric Biggers

From: Eric Biggers <[email protected]>

Now that fscrypt_get_encryption_info() is only called from files in fs/crypto/ (due to all key setup now being handled by higher-level helper functions instead of directly by filesystems), unexport it and move its declaration to fscrypt_private.h.

Reviewed-by Andreas Dilger <[email protected]>

Signed-off-by Eric Biggers <[email protected]>

---
 fs/crypto/fscrypt_private.h | 2 ++
 fs/crypto/keysetup.c        | 1 -
 include/linux/fscrypt.h     | 7 +------
 3 files changed, 3 insertions(+), 7 deletions(-)

fs/crypto/fscrypt_private.h +2 -0

index 16dd55080127a..c1c302656c345 100644
@@ -571,6 +571,8 @@ int fscrypt_derive_dirhash_key(struct fscrypt_info *ci,
 void fscrypt_hash_inode_number(struct fscrypt_info *ci,
 			       const struct fscrypt_master_key *mk);
 
+int fscrypt_get_encryption_info(struct inode *inode);
+
 /**
  * fscrypt_require_key() - require an inode's encryption key
  * @inode: the inode we need the key for

fs/crypto/keysetup.c +0 -1

index 50675b42d5b7c..6339b3069a400 100644
@@ -589,7 +589,6 @@ int fscrypt_get_encryption_info(struct inode *inode)
 		res = 0;
 	return res;
 }
-EXPORT_SYMBOL(fscrypt_get_encryption_info);
 
 /**
  * fscrypt_prepare_new_inode() - prepare to create a new inode in a directory

include/linux/fscrypt.h +1 -6

index a07610f279266..4b163f5e58e9f 100644
@@ -75,7 +75,7 @@ struct fscrypt_operations {
 static inline struct fscrypt_info *fscrypt_get_info(const struct inode *inode)
 {
 	/*
-	 * Pairs with the cmpxchg_release() in fscrypt_get_encryption_info().
+	 * Pairs with the cmpxchg_release() in fscrypt_setup_encryption_info().
 	 * I.e., another task may publish ->i_crypt_info concurrently, executing
 	 * a RELEASE barrier.  We need to use smp_load_acquire() here to safely
 	 * ACQUIRE the memory the other task published.

@@ -200,7 +200,6 @@ int fscrypt_ioctl_remove_key_all_users(struct file *filp, void __user *arg);
 int fscrypt_ioctl_get_key_status(struct file *filp, void __user *arg);
 
 /* keysetup.c */
-int fscrypt_get_encryption_info(struct inode *inode);
 int fscrypt_prepare_new_inode(struct inode *dir, struct inode *inode,
 			      bool *encrypt_ret);
 void fscrypt_put_encryption_info(struct inode *inode);

@@ -408,10 +407,6 @@ static inline int fscrypt_ioctl_get_key_status(struct file *filp,
 }
 
 /* keysetup.c */
-static inline int fscrypt_get_encryption_info(struct inode *inode)
-{
-	return -EOPNOTSUPP;
-}
 
 static inline int fscrypt_prepare_new_inode(struct inode *dir,
 					    struct inode *inode,

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Eric Biggers

author maintainer

2020-12-03 02:23 UTC #9 lore raw

PATCH v2 9/9 fscrypt: allow deleting files with unsupported encryption policy

In reply to Eric Biggers

From: Eric Biggers <[email protected]>

More specifically, this occurs in any of the following cases:

- The encryption context has an unrecognized version number. Current kernels know about v1 and v2, but there could be more versions in the future.

- The encryption context has unrecognized encryption modes (FSCRYPT_MODE_*) or flags (FSCRYPT_POLICY_FLAG_*), an unrecognized combination of modes, or reserved bits set.

- The encryption key has been added and the encryption modes are recognized but aren't available in the crypto API -- for example, a directory is encrypted with FSCRYPT_MODE_ADIANTUM but the kernel doesn't have CONFIG_CRYPTO_ADIANTUM enabled.

Fix this by modifying the key setup logic to treat an unsupported encryption policy in the same way as "key unavailable" in the cases that are required for a recursive delete to work: preparing for a readdir or a dentry lookup, revalidating a dentry, or checking whether an inode has the same encryption policy as its parent directory.

Reviewed-by Andreas Dilger <[email protected]>

Signed-off-by Eric Biggers <[email protected]>

---
 fs/crypto/fname.c           |  8 ++++++--
 fs/crypto/fscrypt_private.h |  4 ++--
 fs/crypto/hooks.c           |  4 ++--
 fs/crypto/keysetup.c        | 19 +++++++++++++++++--
 fs/crypto/policy.c          | 22 ++++++++++++++--------
 include/linux/fscrypt.h     |  9 ++++++---
 6 files changed, 47 insertions(+), 19 deletions(-)

fs/crypto/fname.c +6 -2

index 1fbe6c24d7052..988dadf7a94d5 100644
@@ -404,7 +404,7 @@ int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
 		fname->disk_name.len = iname->len;
 		return 0;
 	}
-	ret = fscrypt_get_encryption_info(dir);
+	ret = fscrypt_get_encryption_info(dir, lookup);
 	if (ret)
 		return ret;

@@ -560,7 +560,11 @@ int fscrypt_d_revalidate(struct dentry *dentry, unsigned int flags)
 		return -ECHILD;
 
 	dir = dget_parent(dentry);
-	err = fscrypt_get_encryption_info(d_inode(dir));
+	/*
+	 * Pass allow_unsupported=true, so that files with an unsupported
+	 * encryption policy can be deleted.
+	 */
+	err = fscrypt_get_encryption_info(d_inode(dir), true);
 	valid = !fscrypt_has_encryption_key(d_inode(dir));
 	dput(dir);

fs/crypto/fscrypt_private.h +2 -2

index c1c302656c345..f0bed6b06fa69 100644
@@ -571,7 +571,7 @@ int fscrypt_derive_dirhash_key(struct fscrypt_info *ci,
 void fscrypt_hash_inode_number(struct fscrypt_info *ci,
 			       const struct fscrypt_master_key *mk);
 
-int fscrypt_get_encryption_info(struct inode *inode);
+int fscrypt_get_encryption_info(struct inode *inode, bool allow_unsupported);
 
 /**
  * fscrypt_require_key() - require an inode's encryption key

@@ -589,7 +589,7 @@ int fscrypt_get_encryption_info(struct inode *inode);
 static inline int fscrypt_require_key(struct inode *inode)
 {
 	if (IS_ENCRYPTED(inode)) {
-		int err = fscrypt_get_encryption_info(inode);
+		int err = fscrypt_get_encryption_info(inode, false);
 
 		if (err)
 			return err;

fs/crypto/hooks.c +2 -2

index 1c16dba222d95..79570e0e8e619 100644
@@ -116,7 +116,7 @@ EXPORT_SYMBOL_GPL(__fscrypt_prepare_lookup);
 
 int __fscrypt_prepare_readdir(struct inode *dir)
 {
-	return fscrypt_get_encryption_info(dir);
+	return fscrypt_get_encryption_info(dir, true);
 }
 EXPORT_SYMBOL_GPL(__fscrypt_prepare_readdir);

@@ -332,7 +332,7 @@ const char *fscrypt_get_symlink(struct inode *inode, const void *caddr,
 	 * Try to set up the symlink's encryption key, but we can continue
 	 * regardless of whether the key is available or not.
 	 */
-	err = fscrypt_get_encryption_info(inode);
+	err = fscrypt_get_encryption_info(inode, false);
 	if (err)
 		return ERR_PTR(err);
 	has_key = fscrypt_has_encryption_key(inode);

fs/crypto/keysetup.c +17 -2

index 6339b3069a400..261293fb70974 100644
@@ -546,6 +546,11 @@ fscrypt_setup_encryption_info(struct inode *inode,
 /**
  * fscrypt_get_encryption_info() - set up an inode's encryption key
  * @inode: the inode to set up the key for.  Must be encrypted.
+ * @allow_unsupported: if %true, treat an unsupported encryption policy (or
+ *		       unrecognized encryption context) the same way as the key
+ *		       being unavailable, instead of returning an error.  Use
+ *		       %false unless the operation being performed is needed in
+ *		       order for files (or directories) to be deleted.
  *
  * Set up ->i_crypt_info, if it hasn't already been done.
  *

@@ -556,7 +561,7 @@ fscrypt_setup_encryption_info(struct inode *inode,
  *	   encryption key is unavailable.  (Use fscrypt_has_encryption_key() to
  *	   distinguish these cases.)  Also can return another -errno code.
  */
-int fscrypt_get_encryption_info(struct inode *inode)
+int fscrypt_get_encryption_info(struct inode *inode, bool allow_unsupported)
 {
 	int res;
 	union fscrypt_context ctx;

@@ -567,24 +572,34 @@ int fscrypt_get_encryption_info(struct inode *inode)
 
 	res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
 	if (res < 0) {
+		if (res == -ERANGE && allow_unsupported)
+			return 0;
 		fscrypt_warn(inode, "Error %d getting encryption context", res);
 		return res;
 	}
 
 	res = fscrypt_policy_from_context(&policy, &ctx, res);
 	if (res) {
+		if (allow_unsupported)
+			return 0;
 		fscrypt_warn(inode,
 			     "Unrecognized or corrupt encryption context");
 		return res;
 	}
 
-	if (!fscrypt_supported_policy(&policy, inode))
+	if (!fscrypt_supported_policy(&policy, inode)) {
+		if (allow_unsupported)
+			return 0;
 		return -EINVAL;
+	}
 
 	res = fscrypt_setup_encryption_info(inode, &policy,
 					    fscrypt_context_nonce(&ctx),
 					    IS_CASEFOLDED(inode) &&
 					    S_ISDIR(inode->i_mode));
+
+	if (res == -ENOPKG && allow_unsupported) /* Algorithm unavailable? */
+		res = 0;
 	if (res == -ENOKEY)
 		res = 0;
 	return res;

fs/crypto/policy.c +14 -8

index faa0f21daa684..a51cef6bd27ff 100644
@@ -590,7 +590,7 @@ EXPORT_SYMBOL_GPL(fscrypt_ioctl_get_nonce);
 int fscrypt_has_permitted_context(struct inode *parent, struct inode *child)
 {
 	union fscrypt_policy parent_policy, child_policy;
-	int err;
+	int err, err1, err2;
 
 	/* No restrictions on file types which are never encrypted */
 	if (!S_ISREG(child->i_mode) && !S_ISDIR(child->i_mode) &&

@@ -620,19 +620,25 @@ int fscrypt_has_permitted_context(struct inode *parent, struct inode *child)
 	 * In any case, if an unexpected error occurs, fall back to "forbidden".
 	 */
 
-	err = fscrypt_get_encryption_info(parent);
+	err = fscrypt_get_encryption_info(parent, true);
 	if (err)
 		return 0;
-	err = fscrypt_get_encryption_info(child);
+	err = fscrypt_get_encryption_info(child, true);
 	if (err)
 		return 0;
 
-	err = fscrypt_get_policy(parent, &parent_policy);
-	if (err)
-		return 0;
+	err1 = fscrypt_get_policy(parent, &parent_policy);
+	err2 = fscrypt_get_policy(child, &child_policy);
 
-	err = fscrypt_get_policy(child, &child_policy);
-	if (err)
+	/*
+	 * Allow the case where the parent and child both have an unrecognized
+	 * encryption policy, so that files with an unrecognized encryption
+	 * policy can be deleted.
+	 */
+	if (err1 == -EINVAL && err2 == -EINVAL)
+		return 1;
+
+	if (err1 || err2)
 		return 0;
 
 	return fscrypt_policies_equal(&parent_policy, &child_policy);

include/linux/fscrypt.h +6 -3

index 4b163f5e58e9f..d23156d1ac949 100644
@@ -753,8 +753,9 @@ static inline int fscrypt_prepare_rename(struct inode *old_dir,
  *
  * Prepare for ->lookup() in a directory which may be encrypted by determining
  * the name that will actually be used to search the directory on-disk.  If the
- * directory's encryption key is available, then the lookup is assumed to be by
- * plaintext name; otherwise, it is assumed to be by no-key name.
+ * directory's encryption policy is supported by this kernel and its encryption
+ * key is available, then the lookup is assumed to be by plaintext name;
+ * otherwise, it is assumed to be by no-key name.
  *
  * This also installs a custom ->d_revalidate() method which will invalidate the
  * dentry if it was created without the key and the key is later added.

@@ -786,7 +787,9 @@ static inline int fscrypt_prepare_lookup(struct inode *dir,
  * form rather than in no-key form.
  *
  * Return: 0 on success; -errno on error.  Note that the encryption key being
- *	   unavailable is not considered an error.
+ *	   unavailable is not considered an error.  It is also not an error if
+ *	   the encryption policy is unsupported by this kernel; that is treated
+ *	   like the key being unavailable, so that files can still be deleted.
  */
 static inline int fscrypt_prepare_readdir(struct inode *dir)
 {

Signature · 8 lines

2.29.2



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Eric Biggers

author maintainer

2020-12-06 23:13 UTC #10 lore raw

In reply to Eric Biggers

Quoted 51 lines · Eric Biggers

Currently it's impossible to delete files that use an unsupported encryption policy, as the kernel will just return an error when performing any operation on the top-level encrypted directory, even just a path lookup into the directory or opening the directory for readdir.
It's desirable to return errors for most operations on files that use an unsupported encryption policy, but the current behavior is too strict. We need to allow enough to delete files, so that people can't be stuck with undeletable files when downgrading kernel versions. That includes allowing directories to be listed and allowing dentries to be looked up.
This series fixes this (on ext4, f2fs, and ubifs) by treating an unsupported encryption policy in the same way as "key unavailable" in the cases that are required for a recursive delete to work.
The actual fix is in patch 9, so see that for more details.
Patches 1-8 are cleanups that prepare for the actual fix by removing direct use of fscrypt_get_encryption_info() by filesystems.
This patchset applies to branch "master" (commit 4a4b8721f1a5) of
https://git.kernel.org/pub/scm/fs/fscrypt/fscrypt.git.
Changed since v1:
- Made some minor updates to commit messages.
- Added Reviewed-by tags.
Eric Biggers (9):
ext4: remove ext4_dir_open()
f2fs: remove f2fs_dir_open()
ubifs: remove ubifs_dir_open()
ext4: don't call fscrypt_get_encryption_info() from dx_show_leaf()
fscrypt: introduce fscrypt_prepare_readdir()
fscrypt: move body of fscrypt_prepare_setattr() out-of-line
fscrypt: move fscrypt_require_key() to fscrypt_private.h
fscrypt: unexport fscrypt_get_encryption_info()
fscrypt: allow deleting files with unsupported encryption policy
 fs/crypto/fname.c           |  8 +++-
 fs/crypto/fscrypt_private.h | 28 ++++++++++++++
 fs/crypto/hooks.c           | 16 +++++++-
 fs/crypto/keysetup.c        | 20 ++++++++--
 fs/crypto/policy.c          | 22 +++++++----
 fs/ext4/dir.c               | 16 ++------
 fs/ext4/namei.c             | 10 +----
 fs/f2fs/dir.c               | 10 +----
 fs/ubifs/dir.c              | 11 +-----
 include/linux/fscrypt.h     | 75 +++++++++++++++++++------------------
 10 files changed, 126 insertions(+), 90 deletions(-)

Quoted 1 line

base-commit: 4a4b8721f1a5e4b01e45b3153c68d5a1014b25de

All applied to fscrypt.git#master for 5.11.

- Eric

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