[PATCH 4.4 041/241] cifs: fix strcat buffer overflow and reduce raciness in smb21_set_oplock_level()

[Greg Kroah-Hartman]

From: Christoph Probst <ker...@probst.it>

commit 6a54b2e002c9d00b398d35724c79f9fe0d9b38fb upstream.

Change strcat to strncpy in the "None" case to fix a buffer overflow
when cinode->oplock is reset to 0 by another thread accessing the same
cinode. It is never valid to append "None" to any other message.

Consolidate multiple writes to cinode->oplock to reduce raciness.

Signed-off-by: Christoph Probst <ker...@probst.it>
Reviewed-by: Pavel Shilovsky <pshi...@microsoft.com>
Signed-off-by: Steve French <stfre...@microsoft.com>
CC: Stable <sta...@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 fs/cifs/smb2ops.c |   14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -1329,26 +1329,28 @@ smb21_set_oplock_level(struct cifsInodeI
                       unsigned int epoch, bool *purge_cache)
 {
        char message[5] = {0};
+       unsigned int new_oplock = 0;
 
        oplock &= 0xFF;
        if (oplock == SMB2_OPLOCK_LEVEL_NOCHANGE)
                return;
 
-       cinode->oplock = 0;
        if (oplock & SMB2_LEASE_READ_CACHING_HE) {
-               cinode->oplock |= CIFS_CACHE_READ_FLG;
+               new_oplock |= CIFS_CACHE_READ_FLG;
                strcat(message, "R");
        }
        if (oplock & SMB2_LEASE_HANDLE_CACHING_HE) {
-               cinode->oplock |= CIFS_CACHE_HANDLE_FLG;
+               new_oplock |= CIFS_CACHE_HANDLE_FLG;
                strcat(message, "H");
        }
        if (oplock & SMB2_LEASE_WRITE_CACHING_HE) {
-               cinode->oplock |= CIFS_CACHE_WRITE_FLG;
+               new_oplock |= CIFS_CACHE_WRITE_FLG;
                strcat(message, "W");
        }
-       if (!cinode->oplock)
-               strcat(message, "None");
+       if (!new_oplock)
+               strncpy(message, "None", sizeof(message));
+
+       cinode->oplock = new_oplock;
        cifs_dbg(FYI, "%s Lease granted on inode %p\n", message,
                 &cinode->vfs_inode);
 }