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>

1 files changed, 6 insertions, 2 deletions

diff --git a/net/sctp/auth.c b/net/sctp/auth.c
index 86366390038a..ddbbf7c81fa1 100644
--- 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;
         }