sctp: Fix out-of-bounds reading in sctp_asoc_get_hmac()

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@vsecurity.com>
Acked-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/sctp/auth.c b/net/sctp/auth.c
index 8636639..ddbbf7c 100644 (file)
--- a/net/sctp/auth.c
+++ b/net/sctp/auth.c
@@ -543,16 +543,20 @@ struct sctp_hmac *sctp_auth_asoc_get_hmac(const struct sctp_association *asoc)
                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;
        }