[PATCH 5.10 040/299] cifs: fix out-of-bound memory access when calling smb3_notify() at mount point

From: Greg Kroah-Hartman
Date: Mon May 10 2021 - 06:53:04 EST

From: Eugene Korenevsky <ekorenevsky@xxxxxxxxxxxxx>

commit a637f4ae037e1e0604ac008564934d63261a8fd1 upstream.

If smb3_notify() is called at mount point of CIFS, build_path_from_dentry()
returns the pointer to kmalloc-ed memory with terminating zero (this is
empty FileName to be passed to SMB2 CREATE request). This pointer is assigned
to the `path` variable.
Then `path + 1` (to skip first backslash symbol) is passed to
cifs_convert_path_to_utf16(). This is incorrect for empty path and causes
out-of-bound memory access.

Get rid of this "increase by one". cifs_convert_path_to_utf16() already
contains the check for leading backslash in the path.

BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=212693
CC: <stable@xxxxxxxxxxxxxxx> # v5.6+
Signed-off-by: Eugene Korenevsky <ekorenevsky@xxxxxxxxxxxxx>
Signed-off-by: Steve French <stfrench@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
fs/cifs/smb2ops.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -2174,7 +2174,7 @@ smb3_notify(const unsigned int xid, stru

cifs_sb = CIFS_SB(inode->i_sb);

- utf16_path = cifs_convert_path_to_utf16(path + 1, cifs_sb);
+ utf16_path = cifs_convert_path_to_utf16(path, cifs_sb);
if (utf16_path == NULL) {
rc = -ENOMEM;
goto notify_exit;