[PATCH 4.9 16/53] cifs: fix strcat buffer overflow and reduce raciness in smb21_set_oplock_level()

Greg Kroah-Hartman
2019-05-23T19:08:35Z

From: Christoph Probst <kernel@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 <kernel@probst.it>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
CC: Stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -1413,26 +1413,28 @@ 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);
}