From: Xin Long <lucien.xin@gmail.com>
Date: Tue, 18 Feb 2020 12:07:53 +0800
Subject: sctp: move the format error check out of __sctp_sf_do_9_1_abort
Git-commit: 245709ec8be89af46ea7ef0444c9c80913999d99
Patch-mainline: 5.6-rc3
References: networking-stable-20_03_01

When T2 timer is to be stopped, the asoc should also be deleted,
otherwise, there will be no chance to call sctp_association_free
and the asoc could last in memory forever.

However, in sctp_sf_shutdown_sent_abort(), after adding the cmd
SCTP_CMD_TIMER_STOP for T2 timer, it may return error due to the
format error from __sctp_sf_do_9_1_abort() and miss adding
SCTP_CMD_ASSOC_FAILED where the asoc will be deleted.

This patch is to fix it by moving the format error check out of
__sctp_sf_do_9_1_abort(), and do it before adding the cmd
SCTP_CMD_TIMER_STOP for T2 timer.

Thanks Hangbin for reporting this issue by the fuzz testing.

v1->v2:
  - improve the comment in the code as Marcelo's suggestion.

Fixes: 96ca468b86b0 ("sctp: check invalid value of length parameter in error cause")
Reported-by: Hangbin Liu <liuhangbin@gmail.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 net/sctp/sm_statefuns.c |   28 ++++++++++++++++++++--------
 1 file changed, 20 insertions(+), 8 deletions(-)

--- a/net/sctp/sm_statefuns.c
+++ b/net/sctp/sm_statefuns.c
@@ -176,6 +176,16 @@ sctp_chunk_length_valid(struct sctp_chun
 	return true;
 }
 
+/* Check for format error in an ABORT chunk */
+static inline bool sctp_err_chunk_valid(struct sctp_chunk *chunk)
+{
+	sctp_errhdr_t *err;
+
+	sctp_walk_errors(err, chunk->chunk_hdr);
+
+	return (void *)err == (void *)chunk->chunk_end;
+}
+
 /**********************************************************
  * These are the state functions for handling chunk events.
  **********************************************************/
@@ -2188,6 +2198,9 @@ sctp_disposition_t sctp_sf_shutdown_pend
 		    sctp_bind_addr_state(&asoc->base.bind_addr, &chunk->dest))
 		return sctp_sf_discard_chunk(net, ep, asoc, type, arg, commands);
 
+	if (!sctp_err_chunk_valid(chunk))
+		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
+
 	return __sctp_sf_do_9_1_abort(net, ep, asoc, type, arg, commands);
 }
 
@@ -2230,6 +2243,9 @@ sctp_disposition_t sctp_sf_shutdown_sent
 		    sctp_bind_addr_state(&asoc->base.bind_addr, &chunk->dest))
 		return sctp_sf_discard_chunk(net, ep, asoc, type, arg, commands);
 
+	if (!sctp_err_chunk_valid(chunk))
+		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
+
 	/* Stop the T2-shutdown timer. */
 	sctp_add_cmd_sf(commands, SCTP_CMD_TIMER_STOP,
 			SCTP_TO(SCTP_EVENT_TIMEOUT_T2_SHUTDOWN));
@@ -2495,6 +2511,9 @@ sctp_disposition_t sctp_sf_do_9_1_abort(
 		    sctp_bind_addr_state(&asoc->base.bind_addr, &chunk->dest))
 		return sctp_sf_discard_chunk(net, ep, asoc, type, arg, commands);
 
+	if (!sctp_err_chunk_valid(chunk))
+		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
+
 	return __sctp_sf_do_9_1_abort(net, ep, asoc, type, arg, commands);
 }
 
@@ -2511,15 +2530,8 @@ static sctp_disposition_t __sctp_sf_do_9
 
 	/* See if we have an error cause code in the chunk.  */
 	len = ntohs(chunk->chunk_hdr->length);
-	if (len >= sizeof(struct sctp_chunkhdr) + sizeof(struct sctp_errhdr)) {
-
-		sctp_errhdr_t *err;
-		sctp_walk_errors(err, chunk->chunk_hdr);
-		if ((void *)err != (void *)chunk->chunk_end)
-			return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
-
+	if (len >= sizeof(struct sctp_chunkhdr) + sizeof(struct sctp_errhdr))
 		error = ((sctp_errhdr_t *)chunk->skb->data)->cause;
-	}
 
 	sctp_add_cmd_sf(commands, SCTP_CMD_SET_SK_ERR, SCTP_ERROR(ECONNRESET));
 	/* ASSOC_FAILED will DELETE_TCB. */