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

Web:        https://git.kernel.org/torvalds/c/07f2c7ab6f8d0a7e7c5764c4e6cc9c52951b9d9c
Commit:     07f2c7ab6f8d0a7e7c5764c4e6cc9c52951b9d9c
Parent:     7b30d51a8f830bd1c1103d31d0314ea6f1106707
Refname:    refs/heads/master
Author:     Alexey Kodanev <[email protected]>
AuthorDate: Fri Feb 9 17:35:23 2018 +0300
Committer:  David S. Miller <[email protected]>
CommitDate: Fri Feb 9 14:31:38 2018 -0500

    sctp: verify size of a new chunk in _sctp_make_chunk()
    
    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.
    
    Signed-off-by: Alexey Kodanev <[email protected]>
    Acked-by: Marcelo Ricardo Leitner <[email protected]>
    Acked-by: Neil Horman <[email protected]>
    Signed-off-by: David S. Miller <[email protected]>
---
 net/sctp/sm_make_chunk.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/net/sctp/sm_make_chunk.c b/net/sctp/sm_make_chunk.c
index 793b05ec692b..d01475f5f710 100644
--- a/net/sctp/sm_make_chunk.c
+++ b/net/sctp/sm_make_chunk.c
@@ -1380,9 +1380,14 @@ static struct sctp_chunk *_sctp_make_chunk(const struct sctp_association *asoc,
 	struct sctp_chunk *retval;
 	struct sk_buff *skb;
 	struct sock *sk;
+	int chunklen;
+
+	chunklen = SCTP_PAD4(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(SCTP_PAD4(sizeof(*chunk_hdr) + paylen), gfp);
+	skb = alloc_skb(chunklen, gfp);
 	if (!skb)
 		goto nodata;
 
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