Re: [PATCH] smb: client: fix UAF and buffer leak in cifs_check_trans2() for malformed secondary T2

On Thu, Aug 13, 2026 at 11:40 AM Frank Sorenson <[email protected]> wrote:
>
> When a valid primary TRANSACT2 response has been received (mid->resp_buf
> set, mid->multiRsp true) and a subsequent secondary response causes
> cifs_check_trans2() to return false -- either because the SMB header is
> invalid (malformed != 0) or because check2ndT2() rejects the PDU --
> handle_mid() overwrites mid->resp_buf with the new buffer (leaking the
> primary buffer) and, because mid->multiRsp is set, skips the
> server->smallbuf/bigbuf NULL-out.  When the user thread frees
> mid->resp_buf, server->smallbuf or server->bigbuf is left dangling; the
> demux thread reuses it for the next packet, resulting in a use-after-free.
>
> Combine both early-exit conditions and, when mid->multiRsp is already
> set, abort the pending transaction inline: set multiEnd, call
> dequeue_mid() with malformed=true, and return true so handle_mid() exits
> without touching mid->resp_buf or the server buffer pointers.
>
> Fixes: 316cf94a910f ("CIFS: Move trans2 processing to ops struct")
> Cc: [email protected] # cifs_check_trans2() is in smb1ops.c on kernels < 7.0
> Signed-off-by: Frank Sorenson <[email protected]>
Will apply it to #for-next.
Thanks!