[PATCH 2/2] smb: client: fix WSL reparse point uid/gid override

[Paulo Alcantara <pc@manguebit.org>]

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 <pc@manguebit.org>
Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Cc: Shyam Prasad N <sprasad@microsoft.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Bharath SM <bharathsm@microsoft.com>
Cc: Namjae Jeon <linkinjeon@kernel.org>
---
 fs/smb/client/reparse.c | 30 +++++++++++++++++++++++++-----
 1 file changed, 25 insertions(+), 5 deletions(-)

diff --git a/fs/smb/client/reparse.c b/fs/smb/client/reparse.c
index 5cc5b0410d48..10ef82d46d86 100644
--- a/fs/smb/client/reparse.c
+++ b/fs/smb/client/reparse.c
@@ -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;
-- 
2.55.0