[PATCH] cifs: fix automount regression of dfs links

[Paulo Alcantara <pc@cjr.nz>]

Unfortunately we can't kfree() the UNC and prefix paths in
cifs_smb3_do_mount() because they could have come from a chased DFS
referral (automount) and we rely on the new values set in cifs_sb->ctx
prior to calling cifs_mount().

Instead, fix smb3_parse_devname() to not leak the UNC and prefix paths
when parsing new share paths.

Cc: <stable@vger.kernel.org> # v5.11+
Fixes: 315db9a05b7a ("cifs: fix leak in cifs_smb3_do_mount() ctx")
Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
---
 fs/cifs/cifsfs.c     |  6 ------
 fs/cifs/connect.c    | 10 +++++++---
 fs/cifs/fs_context.c |  2 ++
 3 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
index 8a6894577697..bfe98136f9c1 100644
--- a/fs/cifs/cifsfs.c
+++ b/fs/cifs/cifsfs.c
@@ -863,12 +863,6 @@ cifs_smb3_do_mount(struct file_system_type *fs_type,
 		goto out;
 	}
 
-	/* cifs_setup_volume_info->smb3_parse_devname() redups UNC & prepath */
-	kfree(cifs_sb->ctx->UNC);
-	cifs_sb->ctx->UNC = NULL;
-	kfree(cifs_sb->ctx->prepath);
-	cifs_sb->ctx->prepath = NULL;
-
 	rc = cifs_setup_volume_info(cifs_sb->ctx, NULL, old_ctx->UNC);
 	if (rc) {
 		root = ERR_PTR(rc);
diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index becd5f807787..ee4a92cbcb29 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -3159,9 +3159,13 @@ static int do_dfs_failover(const char *path, const char *full_path, struct cifs_
 int
 cifs_setup_volume_info(struct smb3_fs_context *ctx, const char *mntopts, const char *devname)
 {
-	int rc = 0;
+	int rc;
 
-	smb3_parse_devname(devname, ctx);
+	rc = smb3_parse_devname(devname, ctx);
+	if (rc) {
+		cifs_dbg(VFS, "%s: failed to parse %s: %d\n", __func__, devname, rc);
+		return rc;
+	}
 
 	if (mntopts) {
 		char *ip;
@@ -3189,7 +3193,7 @@ cifs_setup_volume_info(struct smb3_fs_context *ctx, const char *mntopts, const c
 		return -EINVAL;
 	}
 
-	return rc;
+	return 0;
 }
 
 static int
diff --git a/fs/cifs/fs_context.c b/fs/cifs/fs_context.c
index 1d6e0e15b034..b502a44e15a1 100644
--- a/fs/cifs/fs_context.c
+++ b/fs/cifs/fs_context.c
@@ -476,6 +476,7 @@ smb3_parse_devname(const char *devname, struct smb3_fs_context *ctx)
 
 	/* move "pos" up to delimiter or NULL */
 	pos += len;
+	kfree(ctx->UNC);
 	ctx->UNC = kstrndup(devname, pos - devname, GFP_KERNEL);
 	if (!ctx->UNC)
 		return -ENOMEM;
@@ -490,6 +491,7 @@ smb3_parse_devname(const char *devname, struct smb3_fs_context *ctx)
 	if (!*pos)
 		return 0;
 
+	kfree(ctx->prepath);
 	ctx->prepath = kstrdup(pos, GFP_KERNEL);
 	if (!ctx->prepath)
 		return -ENOMEM;
-- 
2.31.1