[34-longterm 204/209] sctp: Fix out-of-bounds reading in sctp_asoc_get_hmac()

From: Paul Gortmaker
Date: Thu Apr 14 2011 - 14:02:59 EST

From: Dan Rosenberg <drosenberg@xxxxxxxxxxxxx>

| This is a commit scheduled for the next v2.6.34 longterm release. |
| If you see a problem with using this for longterm, please comment.|

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: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
net/sctp/auth.c | 8 ++++++--
1 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/net/sctp/auth.c b/net/sctp/auth.c
index 8636639..ddbbf7c 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) {
+ id = 0;
+ }

/* 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;
+ }


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