linux-kernel - [01/21] cifs: check for bytes_remaining going to zero in CIFS

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Message-Id: <20110519182436.361159813@clark.kroah.org>
Date:	Thu, 19 May 2011 11:23:31 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Jeff Layton <jlayton@...hat.com>,
	Steve French <sfrench@...ibm.com>
Subject: [01/21] cifs: check for bytes_remaining going to zero in CIFS_SessSetup

2.6.32-longterm review patch.  If anyone has any objections, please let us know.

------------------

From: Jeff Layton <jlayton@...hat.com>

commit fcda7f4578bbf9717444ca6da8a421d21489d078 upstream.

It's possible that when we go to decode the string area in the
SESSION_SETUP response, that bytes_remaining will be 0. Decrementing it at
that point will mean that it can go "negative" and wrap. Check for a
bytes_remaining value of 0, and don't try to decode the string area if
that's the case.

Reported-and-Acked-by: David Howells <dhowells@...hat.com>
Signed-off-by: Jeff Layton <jlayton@...hat.com>
Signed-off-by: Steve French <sfrench@...ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 fs/cifs/sess.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/fs/cifs/sess.c
+++ b/fs/cifs/sess.c
@@ -906,7 +906,9 @@ ssetup_ntlmssp_authenticate:
 	}
 
 	/* BB check if Unicode and decode strings */
-	if (smb_buf->Flags2 & SMBFLG2_UNICODE) {
+	if (bytes_remaining == 0) {
+		/* no string area to decode, do nothing */
+	} else if (smb_buf->Flags2 & SMBFLG2_UNICODE) {
 		/* unicode string area must be word-aligned */
 		if (((unsigned long) bcc_ptr - (unsigned long) smb_buf) % 2) {
 			++bcc_ptr;


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