Buffer overflow in CIFS VFS.

Buffer overflow in CIFS VFS.

[Przemyslaw Wegrzyn]

Hello all,

I was looking at CIFS VFS code recently, trying to solve other issue,
just to find something that looks like a buffer overflow  bug.
The problem is in SendReceive() function in transport.c - it memcpy's
message payload into a buffer passed via out_buf param. The function
assumes that all buffers are of size (CIFSMaxBufSize +
MAX_CIFS_HDR_SIZE) , unfortunately it is also called with smaller
(MAX_CIFS_SMALL_BUFFER_SIZE) buffers.

To check this finding I patched Samba server to send oversized logoffX
messages. With ~ 16kB messages the client running 2.6.23.1 crashed upon
unmounting.

I've done a quick fix, available here:
http://czajnick.sitenet.pl/cifs-buffer-overflow-fix.patch.gz

Re: Buffer overflow in CIFS VFS.

[Jörn Engel]

Not everyone has the time to read lkml.  Added Steve to Cc:, just in
case.

On Thu, 8 November 2007 22:20:03 +0100, Przemyslaw Wegrzyn wrote:
> 
> I was looking at CIFS VFS code recently, trying to solve other issue,
> just to find something that looks like a buffer overflow  bug.
> The problem is in SendReceive() function in transport.c - it memcpy's
> message payload into a buffer passed via out_buf param. The function
> assumes that all buffers are of size (CIFSMaxBufSize +
> MAX_CIFS_HDR_SIZE) , unfortunately it is also called with smaller
> (MAX_CIFS_SMALL_BUFFER_SIZE) buffers.
> 
> To check this finding I patched Samba server to send oversized logoffX
> messages. With ~ 16kB messages the client running 2.6.23.1 crashed upon
> unmounting.
> 
> I've done a quick fix, available here:
> http://czajnick.sitenet.pl/cifs-buffer-overflow-fix.patch.gz

Jörn

-- 
When in doubt, punt.  When somebody actually complains, go back and fix it...
The 90% solution is a good thing.
-- Rob Landley