cifs: avoid dup prefix path in dfs_get_automount_devname()

@server->origin_fullpath already contains the tree name + optional
prefix, so avoid calling __build_path_from_dentry_optional_prefix() as
it might end up duplicating prefix path from @cifs_sb->prepath into
final full path.

Instead, generate DFS full path by simply merging
@server->origin_fullpath with dentry's path.

This fixes the following case

	mount.cifs //root/dfs/dir /mnt/ -o ...
	ls /mnt/link

where cifs_dfs_do_automount() will call smb3_parse_devname() with
@devname set to "//root/dfs/dir/link" instead of
"//root/dfs/dir/dir/link".

Fixes: 7ad54b98fc1f ("cifs: use origin fullpath for automounts")
Cc: <stable@vger.kernel.org> # 6.2+
Signed-off-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

diff --git a/fs/cifs/cifs_dfs_ref.c b/fs/cifs/cifs_dfs_ref.c
index cb40074feb3e99bb5a86723fb17d00da744e5f41..0329a907bdfe8acc709069d5bb165ddd1fdcdb72 100644 (file)
--- a/fs/cifs/cifs_dfs_ref.c
+++ b/fs/cifs/cifs_dfs_ref.c
@@ -171,8 +171,6 @@ static struct vfsmount *cifs_dfs_do_automount(struct path *path)
                mnt = ERR_CAST(full_path);
                goto out;
        }
-
-       convert_delimiter(full_path, '/');
        cifs_dbg(FYI, "%s: full_path: %s\n", __func__, full_path);
 
        tmp = *cur_ctx;

diff --git a/fs/cifs/dfs.h b/fs/cifs/dfs.h
index 13f26e01f7b97c33f1bb1398b9853e2fa86e2707..0b8cbf721fff6ed6e9aac7c4f01239f039acefdf 100644 (file)
--- a/fs/cifs/dfs.h
+++ b/fs/cifs/dfs.h
@@ -34,19 +34,33 @@ static inline int dfs_get_referral(struct cifs_mount_ctx *mnt_ctx, const char *p
                              cifs_remap(cifs_sb), path, ref, tl);
 }
 
+/* Return DFS full path out of a dentry set for automount */
 static inline char *dfs_get_automount_devname(struct dentry *dentry, void *page)
 {
        struct cifs_sb_info *cifs_sb = CIFS_SB(dentry->d_sb);
        struct cifs_tcon *tcon = cifs_sb_master_tcon(cifs_sb);
        struct TCP_Server_Info *server = tcon->ses->server;
+       size_t len;
+       char *s;
 
        if (unlikely(!server->origin_fullpath))
                return ERR_PTR(-EREMOTE);
 
-       return __build_path_from_dentry_optional_prefix(dentry, page,
-                                                       server->origin_fullpath,
-                                                       strlen(server->origin_fullpath),
-                                                       true);
+       s = dentry_path_raw(dentry, page, PATH_MAX);
+       if (IS_ERR(s))
+               return s;
+       /* for root, we want "" */
+       if (!s[1])
+               s++;
+
+       len = strlen(server->origin_fullpath);
+       if (s < (char *)page + len)
+               return ERR_PTR(-ENAMETOOLONG);
+
+       s -= len;
+       memcpy(s, server->origin_fullpath, len);
+       convert_delimiter(s, '/');
+       return s;
 }
 
 static inline void dfs_put_root_smb_sessions(struct list_head *head)