[PATCH] [113/275] sctp: Fix out-of-bounds reading in sctp_asoc_get_hmac()

[Andi Kleen]

2.6.35-longterm review patch.  If anyone has any objections, please let me know.

------------------
From: Dan Rosenberg <drosenberg@xxxxxxxxxxxxx>

commit 51e97a12bef19b7e43199fc153cf9bd5f2140362 upstream.

The sctp_asoc_get_hmac() function iterates through a peer's hmac_ids
array and attempts to ensure that only a supported hmac entry is
returned.  The current code fails to do this properly - if the last id
in the array is out of range (greater than SCTP_AUTH_HMAC_ID_MAX), the
id integer remains set after exiting the loop, and the address of an
out-of-bounds entry will be returned and subsequently used in the parent
function, causing potentially ugly memory corruption.  This patch resets
the id integer to 0 on encountering an invalid id so that NULL will be
returned after finishing the loop if no valid ids are found.

Signed-off-by: Dan Rosenberg <drosenberg@xxxxxxxxxxxxx>
Acked-by: Vlad Yasevich <vladislav.yasevich@xxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>
Signed-off-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>

---
 net/sctp/auth.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

Index: linux-2.6.35.y/net/sctp/auth.c
===================================================================
--- linux-2.6.35.y.orig/net/sctp/auth.c	2011-03-29 22:51:23.475122499 -0700
+++ linux-2.6.35.y/net/sctp/auth.c	2011-03-29 23:03:00.538286398 -0700
@@ -543,16 +543,20 @@
 		id = ntohs(hmacs->hmac_ids[i]);
 
 		/* Check the id is in the supported range */
-		if (id > SCTP_AUTH_HMAC_ID_MAX)
+		if (id > SCTP_AUTH_HMAC_ID_MAX) {
+			id = 0;
 			continue;
+		}
 
 		/* See is we support the id.  Supported IDs have name and
 		 * length fields set, so that we can allocated and use
 		 * them.  We can safely just check for name, for without the
 		 * name, we can't allocate the TFM.
 		 */
-		if (!sctp_hmac_list[id].hmac_name)
+		if (!sctp_hmac_list[id].hmac_name) {
+			id = 0;
 			continue;
+		}
 
 		break;
 	}
--
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