Patch "sctp: verify size of a new chunk in _sctp_make_chunk()" has been added to the 3.18-stable tree

This is a note to let you know that I've just added the patch titled

sctp: verify size of a new chunk in _sctp_make_chunk()

to the 3.18-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
sctp-verify-size-of-a-new-chunk-in-_sctp_make_chunk.patch
and it can be found in the queue-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Alexey Kodanev <[email protected]>
Date: Fri, 9 Feb 2018 17:35:23 +0300
Subject: sctp: verify size of a new chunk in _sctp_make_chunk()

From: Alexey Kodanev <[email protected]>

[ Upstream commit 07f2c7ab6f8d0a7e7c5764c4e6cc9c52951b9d9c ]

When SCTP makes INIT or INIT_ACK packet the total chunk length can exceed SCTP_MAX_CHUNK_LEN which leads to kernel panic when transmitting these packets, e.g. the crash on sending INIT_ACK:

[  597.804948] skbuff: skb_over_panic: text:00000000ffae06e4 len:120168
               put:120156 head:000000007aa47635 data:00000000d991c2de
               tail:0x1d640 end:0xfec0 dev:<NULL>
...
[  597.976970] ------------[ cut here ]------------
[  598.033408] kernel BUG at net/core/skbuff.c:104!
[  600.314841] Call Trace:
[  600.345829]  <IRQ>
[  600.371639]  ? sctp_packet_transmit+0x2095/0x26d0 [sctp]
[  600.436934]  skb_put+0x16c/0x200
[  600.477295]  sctp_packet_transmit+0x2095/0x26d0 [sctp]
[  600.540630]  ? sctp_packet_config+0x890/0x890 [sctp]
[  600.601781]  ? __sctp_packet_append_chunk+0x3b4/0xd00 [sctp]
[  600.671356]  ? sctp_cmp_addr_exact+0x3f/0x90 [sctp]
[  600.731482]  sctp_outq_flush+0x663/0x30d0 [sctp]
[  600.788565]  ? sctp_make_init+0xbf0/0xbf0 [sctp]
[  600.845555]  ? sctp_check_transmitted+0x18f0/0x18f0 [sctp]
[  600.912945]  ? sctp_outq_tail+0x631/0x9d0 [sctp]
[  600.969936]  sctp_cmd_interpreter.isra.22+0x3be1/0x5cb0 [sctp]
[  601.041593]  ? sctp_sf_do_5_1B_init+0x85f/0xc30 [sctp]
[  601.104837]  ? sctp_generate_t1_cookie_event+0x20/0x20 [sctp]
[  601.175436]  ? sctp_eat_data+0x1710/0x1710 [sctp]
[  601.233575]  sctp_do_sm+0x182/0x560 [sctp]
[  601.284328]  ? sctp_has_association+0x70/0x70 [sctp]
[  601.345586]  ? sctp_rcv+0xef4/0x32f0 [sctp]
[  601.397478]  ? sctp6_rcv+0xa/0x20 [sctp]

...

Here the chunk size for INIT_ACK packet becomes too big, mostly because of the state cookie (INIT packet has large size with many address parameters), plus additional server parameters.

Later this chunk causes the panic in skb_put_data():

  skb_packet_transmit()
      sctp_packet_pack()
          skb_put_data(nskb, chunk->skb->data, chunk->skb->len);

'nskb' (head skb) was previously allocated with packet->size from u16 'chunk->chunk_hdr->length'.

As suggested by Marcelo we should check the chunk's length in _sctp_make_chunk() before trying to allocate skb for it and discard a chunk if its size bigger than SCTP_MAX_CHUNK_LEN.

---
 net/sctp/sm_make_chunk.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

@@ -1367,10 +1367,14 @@ static struct sctp_chunk *_sctp_make_chu
 	sctp_chunkhdr_t *chunk_hdr;
 	struct sk_buff *skb;
 	struct sock *sk;
+	int chunklen;
+
+	chunklen = sizeof(*chunk_hdr) + paylen;
+	if (chunklen > SCTP_MAX_CHUNK_LEN)
+		goto nodata;
 
 	/* No need to allocate LL here, as this is only a chunk. */
-	skb = alloc_skb(WORD_ROUND(sizeof(sctp_chunkhdr_t) + paylen),
-			GFP_ATOMIC);
+	skb = alloc_skb(chunklen, GFP_ATOMIC);
 	if (!skb)
 		goto nodata;
 

Patches currently in stable-queue which might be from [email protected] are

queue-3.18/sctp-fix-dst-refcnt-leak-in-sctp_v6_get_dst.patch queue-3.18/udplite-fix-partial-checksum-initialization.patch queue-3.18/sctp-verify-size-of-a-new-chunk-in-_sctp_make_chunk.patch