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smb: client: fix uid/gid override in getattr with posix extensions

PATCH Superseded Paulo Alcantara 1 participant 7 messages Sep 6

Subsystems (3)
Stable branch SMB client (CIFS) Kernel SMB3 server (ksmbd)

v3 of 4 Superseded Latest is v4 →

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Paulo Alcantara

author maintainer
#0 lore raw

PATCH v3 1/7 smb: client: fix uid/gid override in getattr with posix extensions

When mounting with 'multiuser,posix' options, cifs_getattr() overrides the server-provided uid/gid with the current process's fsuid/fsgid. This is because the condition only checks for unix extensions (tcon->unix_ext) but not posix extensions (tcon->posix_extensions).

With SMB3 POSIX extensions, the server provides real uid/gid values just like with unix extensions, so they should be preserved rather than replaced with the caller's credentials.

Add a tcon->posix_extensions check to the condition so that uid/gid from the server are properly reported in stat results.

Reported-by Arthur Lesuisse <[email protected]>
Closes https://lore.kernel.org/r/DB9P190MB2012266F6B8DECBE5D26A1798DB52@DB9P190MB2012.EURP190.PROD.OUTLOOK.COM open here
Suggested-by Arthur Lesuisse <[email protected]>
Signed-off-by Paulo Alcantara <[email protected]>
Cc Namjae Jeon <[email protected]>
Cc Ronnie Sahlberg <[email protected]>
Cc Shyam Prasad N <[email protected]>
Cc Tom Talpey <[email protected]>
Cc Bharath SM <[email protected]>
Cc [email protected]
---
 fs/smb/client/inode.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)
fs/smb/client/inode.c +4 -4
index 12ed8db10e00..49f9993ad567 100644
@@ -2992,14 +2992,14 @@ int cifs_getattr(struct mnt_idmap *idmap, const struct path *path,
 		stat->attributes |= STATX_ATTR_ENCRYPTED;
 
 	/*
-	 * If on a multiuser mount without unix extensions or cifsacl being
-	 * enabled, and the admin hasn't overridden them, set the ownership
-	 * to the fsuid/fsgid of the current process.
+	 * If on a multiuser mount without unix extensions, posix extensions
+	 * or cifsacl being enabled, and the admin hasn't overridden them,
+	 * set the ownership to the fsuid/fsgid of the current process.
 	 */
 	sbflags = cifs_sb_flags(cifs_sb);
 	if ((sbflags & CIFS_MOUNT_MULTIUSER) &&
 	    !(sbflags & CIFS_MOUNT_CIFS_ACL) &&
-	    !tcon->unix_ext) {
+	    !tcon->unix_ext && !tcon->posix_extensions) {
 		if (!(sbflags & CIFS_MOUNT_OVERR_UID))
 			stat->uid = current_fsuid();
 		if (!(sbflags & CIFS_MOUNT_OVERR_GID))
Signature · 1 line
2.55.0
author maintainer
#1 lore raw

PATCH v3 2/7 smb: client: honor forceuid/forcegid when mapping SIDs to uid/gid

When the administrator mounts with forceuid or forcegid (uid=/gid= mount options), they expect all files to appear owned by the specified user/group. However, several code paths unconditionally called sid_to_id() to overwrite cf_uid/cf_gid with server-provided values, ignoring the administrator's explicit override:

- smb311_posix_info_to_fattr() (stat via POSIX extensions)
- cifs_posix_to_fattr() (readdir via POSIX extensions)
- parse_sec_desc() (CIFS ACL ownership mapping)

This allowed an untrusted server to dictate local file ownership even when the mount was configured to force specific uid/gid values.

Fix all three call sites to check CIFS_MOUNT_OVERR_UID and CIFS_MOUNT_OVERR_GID before calling sid_to_id(), following the same pattern already used by cifs_unix_basic_to_fattr() for unix extensions.

Closes https://sashiko.dev/#/patchset/20260906155816.603278-1-pc%40manguebit.org
Signed-off-by Paulo Alcantara <[email protected]>
Cc Namjae Jeon <[email protected]>
Cc Ronnie Sahlberg <[email protected]>
Cc Shyam Prasad N <[email protected]>
Cc Tom Talpey <[email protected]>
Cc Bharath SM <[email protected]>
Cc [email protected]
---
 fs/smb/client/cifsacl.c | 29 ++++++++++++++++++-----------
 fs/smb/client/inode.c   |  9 +++++++--
 fs/smb/client/readdir.c |  9 +++++++--
 3 files changed, 32 insertions(+), 15 deletions(-)
fs/smb/client/cifsacl.c +18 -11
index 213a421bf8e9..def8908dd7e9 100644
@@ -1346,6 +1346,7 @@ static int parse_sec_desc(struct cifs_sb_info *cifs_sb,
 {
 	int rc = 0;
 	struct smb_sid *owner_sid_ptr, *group_sid_ptr;
+	unsigned int sbflags = cifs_sb_flags(cifs_sb);
 	struct smb_acl *dacl_ptr; /* no need for SACL ptr */
 	char *end_of_acl;
 	__u32 dacloffset, osidoffset, gsidoffset;

@@ -1364,17 +1365,21 @@ static int parse_sec_desc(struct cifs_sb_info *cifs_sb,
 	cifs_dbg(NOISY, "revision %d type 0x%x ooffset 0x%x goffset 0x%x sacloffset 0x%x dacloffset 0x%x\n",
 		 pntsd->revision, pntsd->type, osidoffset, gsidoffset,
 		 le32_to_cpu(pntsd->sacloffset), dacloffset);
-/*	cifs_dump_mem("owner_sid: ", owner_sid_ptr, 64); */
+	fattr->cf_uid = cifs_sb->ctx->linux_uid;
+	fattr->cf_gid = cifs_sb->ctx->linux_gid;
+
 	rc = sid_from_sd(pntsd, acl_len, osidoffset, &owner_sid_ptr);
 	if (rc) {
 		cifs_dbg(FYI, "%s: Error %d parsing Owner SID\n", __func__, rc);
 		return rc;
 	}
-	rc = sid_to_id(cifs_sb, owner_sid_ptr, fattr, SIDOWNER);
-	if (rc) {
-		cifs_dbg(FYI, "%s: Error %d mapping Owner SID to uid\n",
-			 __func__, rc);
-		return rc;
+	if (!(sbflags & CIFS_MOUNT_OVERR_UID)) {
+		rc = sid_to_id(cifs_sb, owner_sid_ptr, fattr, SIDOWNER);
+		if (rc) {
+			cifs_dbg(FYI, "%s: Error %d mapping Owner SID to uid\n",
+				 __func__, rc);
+			return rc;
+		}
 	}
 
 	rc = sid_from_sd(pntsd, acl_len, gsidoffset, &group_sid_ptr);

@@ -1383,11 +1388,13 @@ static int parse_sec_desc(struct cifs_sb_info *cifs_sb,
 			 __func__, rc);
 		return rc;
 	}
-	rc = sid_to_id(cifs_sb, group_sid_ptr, fattr, SIDGROUP);
-	if (rc) {
-		cifs_dbg(FYI, "%s: Error %d mapping Group SID to gid\n",
-			 __func__, rc);
-		return rc;
+	if (!(sbflags & CIFS_MOUNT_OVERR_GID)) {
+		rc = sid_to_id(cifs_sb, group_sid_ptr, fattr, SIDGROUP);
+		if (rc) {
+			cifs_dbg(FYI, "%s: Error %d mapping Group SID to gid\n",
+				 __func__, rc);
+			return rc;
+		}
 	}
 
 	if (dacloffset) {
fs/smb/client/inode.c +7 -2
index 49f9993ad567..1fe0ef0a95db 100644
@@ -851,6 +851,7 @@ static void smb311_posix_info_to_fattr(struct cifs_fattr *fattr,
 	struct smb311_posix_qinfo *info = &data->posix_fi;
 	struct cifs_sb_info *cifs_sb = CIFS_SB(sb);
 	struct cifs_tcon *tcon = cifs_sb_master_tcon(cifs_sb);
+	unsigned int sbflags = cifs_sb_flags(cifs_sb);
 
 	memset(fattr, 0, sizeof(*fattr));
 

@@ -895,8 +896,12 @@ static void smb311_posix_info_to_fattr(struct cifs_fattr *fattr,
 		fattr->cf_symlink_target = data->symlink_target;
 		data->symlink_target = NULL;
 	}
-	sid_to_id(cifs_sb, &data->posix_owner, fattr, SIDOWNER);
-	sid_to_id(cifs_sb, &data->posix_group, fattr, SIDGROUP);
+	fattr->cf_uid = cifs_sb->ctx->linux_uid;
+	fattr->cf_gid = cifs_sb->ctx->linux_gid;
+	if (!(sbflags & CIFS_MOUNT_OVERR_UID))
+		sid_to_id(cifs_sb, &data->posix_owner, fattr, SIDOWNER);
+	if (!(sbflags & CIFS_MOUNT_OVERR_GID))
+		sid_to_id(cifs_sb, &data->posix_group, fattr, SIDGROUP);
 
 	cifs_dbg(FYI, "POSIX query info: mode 0x%x uniqueid 0x%llx nlink %d\n",
 		fattr->cf_mode, fattr->cf_uniqueid, fattr->cf_nlink);
fs/smb/client/readdir.c +7 -2
index 32a75afca8f5..1ea84f4ada39 100644
@@ -242,6 +242,7 @@ static void
 cifs_posix_to_fattr(struct cifs_fattr *fattr, struct smb2_posix_info *info,
 		    struct cifs_sb_info *cifs_sb)
 {
+	unsigned int sbflags = cifs_sb_flags(cifs_sb);
 	struct smb2_posix_info_parsed parsed;
 
 	posix_info_parse(info, NULL, &parsed);

@@ -281,8 +282,12 @@ cifs_posix_to_fattr(struct cifs_fattr *fattr, struct smb2_posix_info *info,
 		 le32_to_cpu(info->ReparseTag),
 		 le32_to_cpu(info->Mode));
 
-	sid_to_id(cifs_sb, &parsed.owner, fattr, SIDOWNER);
-	sid_to_id(cifs_sb, &parsed.group, fattr, SIDGROUP);
+	fattr->cf_uid = cifs_sb->ctx->linux_uid;
+	fattr->cf_gid = cifs_sb->ctx->linux_gid;
+	if (!(sbflags & CIFS_MOUNT_OVERR_UID))
+		sid_to_id(cifs_sb, &parsed.owner, fattr, SIDOWNER);
+	if (!(sbflags & CIFS_MOUNT_OVERR_GID))
+		sid_to_id(cifs_sb, &parsed.group, fattr, SIDGROUP);
 }
 
 static void __dir_info_to_fattr(struct cifs_fattr *fattr, const void *info)
Signature · 1 line
2.55.0
author maintainer
#2 lore raw

PATCH v3 3/7 smb: client: fix WSL reparse point uid/gid override

In reply to Paulo Alcantara

wsl_to_fattr() unconditionally overwrites cf_uid/cf_gid with values from WSL extended attributes ($LXUID/$LXGID), ignoring the administrator's forceuid/forcegid mount options. It also doesn't initialize the uid/gid defaults, so callers that invoke it before setting cf_uid/cf_gid (e.g. smb311_posix_info_to_fattr()) would leave zeroed values when forceuid/forcegid is set.

Additionally, when UNIX or SMB3 POSIX extensions are negotiated, the server already provides authoritative uid/gid and mode values through the extensions themselves, making the WSL reparse point EA values ($LXUID, $LXGID, $LXMOD) redundant and potentially conflicting.

Fix this by:
- Initializing cf_uid/cf_gid to the mount-specified linux_uid/ linux_gid defaults
- Gating the $LXUID/$LXGID EA parsing on CIFS_MOUNT_OVERR_UID/ CIFS_MOUNT_OVERR_GID
- Skipping $LXUID, $LXGID, and $LXMOD EA parsing entirely when UNIX or POSIX extensions are active (only $LXDEV is still parsed for device major/minor numbers)

Signed-off-by Paulo Alcantara <[email protected]>
Cc Namjae Jeon <[email protected]>
Cc Ronnie Sahlberg <[email protected]>
Cc Shyam Prasad N <[email protected]>
Cc Tom Talpey <[email protected]>
Cc Bharath SM <[email protected]>
Cc [email protected]
---
 fs/smb/client/reparse.c | 30 +++++++++++++++++++++++++-----
 1 file changed, 25 insertions(+), 5 deletions(-)
fs/smb/client/reparse.c +25 -5
index 5cc5b0410d48..10ef82d46d86 100644
@@ -1137,10 +1137,15 @@ static bool wsl_to_fattr(struct cifs_open_info_data *data,
 			 struct cifs_sb_info *cifs_sb,
 			 u32 tag, struct cifs_fattr *fattr)
 {
+	struct cifs_tcon *tcon = cifs_sb_master_tcon(cifs_sb);
+	unsigned int sbflags = cifs_sb_flags(cifs_sb);
 	struct smb2_file_full_ea_info *ea;
 	bool have_xattr_dev = false;
 	u32 next = 0;
 
+	fattr->cf_uid = cifs_sb->ctx->linux_uid;
+	fattr->cf_gid = cifs_sb->ctx->linux_gid;
+
 	switch (tag) {
 	case IO_REPARSE_TAG_LX_SYMLINK:
 		fattr->cf_mode |= S_IFLNK;

@@ -1177,11 +1182,26 @@ static bool wsl_to_fattr(struct cifs_open_info_data *data,
 		nlen = ea->ea_name_length;
 		v = (void *)((u8 *)ea->ea_data + ea->ea_name_length + 1);
 
-		if (!strncmp(name, SMB2_WSL_XATTR_UID, nlen))
-			fattr->cf_uid = wsl_make_kuid(cifs_sb, v);
-		else if (!strncmp(name, SMB2_WSL_XATTR_GID, nlen))
-			fattr->cf_gid = wsl_make_kgid(cifs_sb, v);
-		else if (!strncmp(name, SMB2_WSL_XATTR_MODE, nlen)) {
+		/*
+		 * Skip uid/gid/mode when UNIX or POSIX extensions are
+		 * active since the server provides these values through
+		 * the extensions themselves.
+		 */
+		if (tcon->unix_ext || tcon->posix_extensions) {
+			if (!strncmp(name, SMB2_WSL_XATTR_DEV, nlen)) {
+				fattr->cf_rdev = reparse_mkdev(v);
+				have_xattr_dev = true;
+			}
+			continue;
+		}
+
+		if (!strncmp(name, SMB2_WSL_XATTR_UID, nlen)) {
+			if (!(sbflags & CIFS_MOUNT_OVERR_UID))
+				fattr->cf_uid = wsl_make_kuid(cifs_sb, v);
+		} else if (!strncmp(name, SMB2_WSL_XATTR_GID, nlen)) {
+			if (!(sbflags & CIFS_MOUNT_OVERR_GID))
+				fattr->cf_gid = wsl_make_kgid(cifs_sb, v);
+		} else if (!strncmp(name, SMB2_WSL_XATTR_MODE, nlen)) {
 			/* File type in reparse point tag and in xattr mode must match. */
 			if (S_DT(fattr->cf_mode) != S_DT(le32_to_cpu(*(__le32 *)v)))
 				return false;
Signature · 1 line
2.55.0
author maintainer
#3 lore raw

PATCH v3 4/7 smb: client: avoid using uninitialized SIDs in cifs_posix_to_fattr()

In reply to Paulo Alcantara

cifs_posix_to_fattr() ignores the return value of posix_info_parse(). When a malformed POSIX directory entry is encountered (e.g. invalid SID lengths from an untrusted server), posix_info_parse() returns -1 without populating the 'parsed' struct. The uninitialized stack memory in parsed.owner and parsed.group is then passed to sid_to_id(), which processes the garbage bytes and passes them to request_key() to construct a SID string, potentially leaking kernel stack contents to the userspace idmap daemon.

Fix this by checking the return value and skipping the SID-to-id mapping when parsing fails. The remaining fattr fields (timestamps, mode, etc.) are populated directly from the 'info' pointer so they are unaffected.

Closes https://sashiko.dev/#/patchset/20260906172005.627163-1-pc%40manguebit.org
Closes https://sashiko.dev/#/patchset/20260906181540.647469-1-pc%40manguebit.org
Signed-off-by Paulo Alcantara <[email protected]>
Cc Namjae Jeon <[email protected]>
Cc Ronnie Sahlberg <[email protected]>
Cc Shyam Prasad N <[email protected]>
Cc Tom Talpey <[email protected]>
Cc Bharath SM <[email protected]>
Cc [email protected]
---
 fs/smb/client/readdir.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)
fs/smb/client/readdir.c +11 -5
index 1ea84f4ada39..9530e5b01564 100644
@@ -244,8 +244,9 @@ cifs_posix_to_fattr(struct cifs_fattr *fattr, struct smb2_posix_info *info,
 {
 	unsigned int sbflags = cifs_sb_flags(cifs_sb);
 	struct smb2_posix_info_parsed parsed;
+	int rc;
 
-	posix_info_parse(info, NULL, &parsed);
+	rc = posix_info_parse(info, NULL, &parsed);
 
 	memset(fattr, 0, sizeof(*fattr));
 	fattr->cf_uniqueid = le64_to_cpu(info->Inode);

@@ -284,10 +285,15 @@ cifs_posix_to_fattr(struct cifs_fattr *fattr, struct smb2_posix_info *info,
 
 	fattr->cf_uid = cifs_sb->ctx->linux_uid;
 	fattr->cf_gid = cifs_sb->ctx->linux_gid;
-	if (!(sbflags & CIFS_MOUNT_OVERR_UID))
-		sid_to_id(cifs_sb, &parsed.owner, fattr, SIDOWNER);
-	if (!(sbflags & CIFS_MOUNT_OVERR_GID))
-		sid_to_id(cifs_sb, &parsed.group, fattr, SIDGROUP);
+	if (rc < 0) {
+		cifs_dbg(VFS, "%s: failed to parse SIDs: %d\n",
+			 __func__, rc);
+	} else {
+		if (!(sbflags & CIFS_MOUNT_OVERR_UID))
+			sid_to_id(cifs_sb, &parsed.owner, fattr, SIDOWNER);
+		if (!(sbflags & CIFS_MOUNT_OVERR_GID))
+			sid_to_id(cifs_sb, &parsed.group, fattr, SIDGROUP);
+	}
 }
 
 static void __dir_info_to_fattr(struct cifs_fattr *fattr, const void *info)
Signature · 1 line
2.55.0
author maintainer
#4 lore raw

PATCH v3 5/7 smb: client: fix file type corruption in wsl_to_fattr()

In reply to Paulo Alcantara

Setting the file type in cf_mode without clearing the existing S_IFMT bits first is wrong as it corrupts the file type when cf_mode already has type bits set (e.g. S_IFREG | S_IFCHR == S_IFLNK).

Clear S_IFMT before the switch statement.

Closes https://sashiko.dev/#/patchset/20260906172005.627163-1-pc%40manguebit.org
Signed-off-by Paulo Alcantara <[email protected]>
Cc Namjae Jeon <[email protected]>
Cc Ronnie Sahlberg <[email protected]>
Cc Shyam Prasad N <[email protected]>
Cc Tom Talpey <[email protected]>
Cc Bharath SM <[email protected]>
Cc [email protected]
---
 fs/smb/client/reparse.c | 1 +
 1 file changed, 1 insertion(+)
fs/smb/client/reparse.c +1 -0
index 10ef82d46d86..9edc379bd686 100644
@@ -1146,6 +1146,7 @@ static bool wsl_to_fattr(struct cifs_open_info_data *data,
 	fattr->cf_uid = cifs_sb->ctx->linux_uid;
 	fattr->cf_gid = cifs_sb->ctx->linux_gid;
 
+	fattr->cf_mode &= ~S_IFMT;
 	switch (tag) {
 	case IO_REPARSE_TAG_LX_SYMLINK:
 		fattr->cf_mode |= S_IFLNK;
Signature · 1 line
2.55.0
author maintainer
#5 lore raw

PATCH v3 6/7 smb: client: fix file type corruption in posix_reparse_to_fattr()

In reply to Paulo Alcantara

Setting the file type in cf_mode without clearing the existing S_IFMT bits first is wrong as it corrupts the file type when cf_mode already has type bits set (e.g. S_IFREG | S_IFCHR == S_IFLNK).

Use a local ftype variable to collect the new file type and apply it after validation succeeds, clearing S_IFMT and setting the new type in a single assignment. This avoids stripping cf_mode on malformed reparse points where the function returns false early.

Closes https://sashiko.dev/#/patchset/20260906172005.627163-1-pc%40manguebit.org
Signed-off-by Paulo Alcantara <[email protected]>
Cc Namjae Jeon <[email protected]>
Cc Ronnie Sahlberg <[email protected]>
Cc Shyam Prasad N <[email protected]>
Cc Tom Talpey <[email protected]>
Cc Bharath SM <[email protected]>
Cc [email protected]
---
 fs/smb/client/reparse.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)
fs/smb/client/reparse.c +7 -5
index 9edc379bd686..b44dbeca2419 100644
@@ -1226,6 +1226,7 @@ static bool posix_reparse_to_fattr(struct cifs_sb_info *cifs_sb,
 				   struct cifs_open_info_data *data)
 {
 	struct reparse_nfs_data_buffer *buf = (struct reparse_nfs_data_buffer *)data->reparse.buf;
+	umode_t ftype;
 
 	if (buf == NULL)
 		return true;

@@ -1241,7 +1242,7 @@ static bool posix_reparse_to_fattr(struct cifs_sb_info *cifs_sb,
 			WARN_ON_ONCE(1);
 			return false;
 		}
-		fattr->cf_mode |= S_IFCHR;
+		ftype = S_IFCHR;
 		fattr->cf_rdev = reparse_mkdev(buf->DataBuffer);
 		break;
 	case NFS_SPECFILE_BLK:

@@ -1249,22 +1250,23 @@ static bool posix_reparse_to_fattr(struct cifs_sb_info *cifs_sb,
 			WARN_ON_ONCE(1);
 			return false;
 		}
-		fattr->cf_mode |= S_IFBLK;
+		ftype = S_IFBLK;
 		fattr->cf_rdev = reparse_mkdev(buf->DataBuffer);
 		break;
 	case NFS_SPECFILE_FIFO:
-		fattr->cf_mode |= S_IFIFO;
+		ftype = S_IFIFO;
 		break;
 	case NFS_SPECFILE_SOCK:
-		fattr->cf_mode |= S_IFSOCK;
+		ftype = S_IFSOCK;
 		break;
 	case NFS_SPECFILE_LNK:
-		fattr->cf_mode |= S_IFLNK;
+		ftype = S_IFLNK;
 		break;
 	default:
 		WARN_ON_ONCE(1);
 		return false;
 	}
+	fattr->cf_mode = (fattr->cf_mode & ~S_IFMT) | ftype;
 	return true;
 }
Signature · 1 line
2.55.0
author maintainer
#6 lore raw

PATCH v3 7/7 smb: client: fix file type corruption in cifs_reparse_point_to_fattr()

In reply to Paulo Alcantara

Setting the file type in cf_mode without clearing the existing S_IFMT bits first is wrong as it corrupts the file type when cf_mode already has type bits set (e.g. S_IFREG | S_IFLNK == S_IFDIR | S_IFREG).

Clear S_IFMT before setting S_IFLNK for native and SMB1 symlinks.

Closes https://sashiko.dev/#/patchset/20260906181540.647469-1-pc%40manguebit.org
Signed-off-by Paulo Alcantara <[email protected]>
Cc Namjae Jeon <[email protected]>
Cc Ronnie Sahlberg <[email protected]>
Cc Shyam Prasad N <[email protected]>
Cc Tom Talpey <[email protected]>
Cc Bharath SM <[email protected]>
Cc [email protected]
---
 fs/smb/client/reparse.c | 1 +
 1 file changed, 1 insertion(+)
fs/smb/client/reparse.c +1 -0
index b44dbeca2419..5a5211fd639c 100644
@@ -1294,6 +1294,7 @@ bool cifs_reparse_point_to_fattr(struct cifs_sb_info *cifs_sb,
 		break;
 	case 0: /* SMB1 symlink */
 	case IO_REPARSE_TAG_SYMLINK:
+		fattr->cf_mode &= ~S_IFMT;
 		fattr->cf_mode |= S_IFLNK;
 		break;
 	default:
Signature · 1 line
2.55.0