[PATCH net] sctp: fix uninit-value in sctp_inq_pop()

[Nikita Zhandarovich]

Syzbot identified a case [1] of uninitialized memory usage in
sctp_inq_pop(), specifically in 'ch->length'.

Fix the issue by ensuring that 'ch->length' reflects the size of
'sctp_chunkhdr *ch' before accessing it.

[1]
BUG: KMSAN: uninit-value in sctp_inq_pop+0x1597/0x1910 net/sctp/inqueue.c:205
 sctp_inq_pop+0x1597/0x1910 net/sctp/inqueue.c:205
 sctp_assoc_bh_rcv+0x1a7/0xc50 net/sctp/associola.c:997
 sctp_inq_push+0x23e/0x2b0 net/sctp/inqueue.c:80
 sctp_backlog_rcv+0x394/0xd80 net/sctp/input.c:331
 sk_backlog_rcv include/net/sock.h:1115 [inline]
 __release_sock+0x207/0x570 net/core/sock.c:2911
 release_sock+0x6b/0x1e0 net/core/sock.c:3478
 sctp_wait_for_connect+0x486/0x810 net/sctp/socket.c:9325
 sctp_sendmsg_to_asoc+0x1ea7/0x1ee0 net/sctp/socket.c:1884
 ...

Uninit was stored to memory at:
 sctp_inq_pop+0x151a/0x1910 net/sctp/inqueue.c:201
 sctp_assoc_bh_rcv+0x1a7/0xc50 net/sctp/associola.c:997
 sctp_inq_push+0x23e/0x2b0 net/sctp/inqueue.c:80
 sctp_backlog_rcv+0x394/0xd80 net/sctp/input.c:331
 sk_backlog_rcv include/net/sock.h:1115 [inline]
 __release_sock+0x207/0x570 net/core/sock.c:2911
 release_sock+0x6b/0x1e0 net/core/sock.c:3478
 sctp_wait_for_connect+0x486/0x810 net/sctp/socket.c:9325
 sctp_sendmsg_to_asoc+0x1ea7/0x1ee0 net/sctp/socket.c:1884
 ...

Uninit was created at:
 slab_post_alloc_hook+0x12d/0xb60 mm/slab.h:716
 slab_alloc_node mm/slub.c:3451 [inline]
 __kmem_cache_alloc_node+0x4ff/0x8b0 mm/slub.c:3490
 __do_kmalloc_node mm/slab_common.c:965 [inline]
 __kmalloc_node_track_caller+0x118/0x3c0 mm/slab_common.c:986
 kmalloc_reserve+0x248/0x470 net/core/skbuff.c:585
 __alloc_skb+0x318/0x740 net/core/skbuff.c:654
 alloc_skb include/linux/skbuff.h:1288 [inline]
 sctp_packet_pack net/sctp/output.c:472 [inline]
 sctp_packet_transmit+0x1729/0x4150 net/sctp/output.c:621
 sctp_outq_flush_transports net/sctp/outqueue.c:1173 [inline]
 ...

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-and-tested-by: syzbot+70a42f45e76bede082be@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=70a42f45e76bede082be
Signed-off-by: Nikita Zhandarovich <n.zhandarovich@xxxxxxxxxx>
---
 net/sctp/inqueue.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/sctp/inqueue.c b/net/sctp/inqueue.c
index 7182c5a450fb..98ce9524c87c 100644
--- a/net/sctp/inqueue.c
+++ b/net/sctp/inqueue.c
@@ -197,6 +197,7 @@ struct sctp_chunk *sctp_inq_pop(struct sctp_inq *queue)
 		}
 	}
 
+	ch->length = htons(sizeof(*ch));
 	chunk->chunk_hdr = ch;
 	chunk->chunk_end = ((__u8 *)ch) + SCTP_PAD4(ntohs(ch->length));
 	skb_pull(chunk->skb, sizeof(*ch));
-- 
2.25.1