[patch 2.6.21-rc3] [smbfs] "double free" memory corruption in smbfs

[Vasily Averin <vvs@sw.ru>]

smbfs allocates rq_trans2buffer to handle server's multi transaction2 response
messages. As struct smb_request may be reused, rq_trans2buffer is freed before
each new request. However if last servers's response is not multi but single
trans2 message then new rq_trans2buffer is not allocated but last smb_rput still
tries to free it again.
To prevent this issue rq_trans2buffer pointer should be set to NULL after kfree.

Signed-off-by:	Vasily Averin <vvs@sw.ru>

--- 2.6.21-rc3/fs/smbfs/request.c	2007-03-13 14:22:53.000000000 +0300
+++ 2.6.21-rc3/fs/smbfs/request.c	2007-03-14 11:44:18.000000000 +0300
@@ -181,6 +181,7 @@ static int smb_setup_request(struct smb_
 	req->rq_errno = 0;
 	req->rq_fragment = 0;
 	kfree(req->rq_trans2buffer);
+	req->rq_trans2buffer = NULL;

 	return 0;
 }