Re: [PATCH 4.4 31/36] sctp: verify size of a new chunk in _sctp_make_chunk()

[Ben Hutchings]

On Fri, 2018-03-09 at 16:18 -0800, Greg Kroah-Hartman wrote:
> 4.4-stable review patch.ÂÂIf anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Alexey Kodanev <alexey.kodanev@xxxxxxxxxx>
> 
> 
> [ 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:
> 
> [ÂÂ597.804948] skbuff: skb_over_panic: text:00000000ffae06e4 len:120168
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂput:120156 head:000000007aa47635 data:00000000d991c2de
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂtail:0x1d640 end:0xfec0 dev:<NULL>
> ...
> [ÂÂ597.976970] ------------[ cut here ]------------
> [ÂÂ598.033408] kernel BUG at net/core/skbuff.c:104!
> [ÂÂ600.314841] Call Trace:
> [ÂÂ600.345829]ÂÂ<IRQ>
> [ÂÂ600.371639]ÂÂ? sctp_packet_transmit+0x2095/0x26d0 [sctp]
> [ÂÂ600.436934]ÂÂskb_put+0x16c/0x200
> [ÂÂ600.477295]ÂÂsctp_packet_transmit+0x2095/0x26d0 [sctp]
> [ÂÂ600.540630]ÂÂ? sctp_packet_config+0x890/0x890 [sctp]
> [ÂÂ600.601781]ÂÂ? __sctp_packet_append_chunk+0x3b4/0xd00 [sctp]
> [ÂÂ600.671356]ÂÂ? sctp_cmp_addr_exact+0x3f/0x90 [sctp]
> [ÂÂ600.731482]ÂÂsctp_outq_flush+0x663/0x30d0 [sctp]
> [ÂÂ600.788565]ÂÂ? sctp_make_init+0xbf0/0xbf0 [sctp]
> [ÂÂ600.845555]ÂÂ? sctp_check_transmitted+0x18f0/0x18f0 [sctp]
> [ÂÂ600.912945]ÂÂ? sctp_outq_tail+0x631/0x9d0 [sctp]
> [ÂÂ600.969936]ÂÂsctp_cmd_interpreter.isra.22+0x3be1/0x5cb0 [sctp]
> [ÂÂ601.041593]ÂÂ? sctp_sf_do_5_1B_init+0x85f/0xc30 [sctp]
> [ÂÂ601.104837]ÂÂ? sctp_generate_t1_cookie_event+0x20/0x20 [sctp]
> [ÂÂ601.175436]ÂÂ? sctp_eat_data+0x1710/0x1710 [sctp]
> [ÂÂ601.233575]ÂÂsctp_do_sm+0x182/0x560 [sctp]
> [ÂÂ601.284328]ÂÂ? sctp_has_association+0x70/0x70 [sctp]
> [ÂÂ601.345586]ÂÂ? sctp_rcv+0xef4/0x32f0 [sctp]
> [ÂÂ601.397478]ÂÂ? 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():
> 
> Â skb_packet_transmit()
> ÂÂÂÂÂÂsctp_packet_pack()
> ÂÂÂÂÂÂÂÂÂÂskb_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 <alexey.kodanev@xxxxxxxxxx>
> > Acked-by: Marcelo Ricardo Leitner <marcelo.leinter@xxxxxxxxx>
> > Acked-by: Neil Horman <nhorman@xxxxxxxxxxxxx>
> > Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> ---
> Ânet/sctp/sm_make_chunk.c |ÂÂÂÂ8 ++++++--
> Â1 file changed, 6 insertions(+), 2 deletions(-)
> 
> --- a/net/sctp/sm_make_chunk.c
> +++ b/net/sctp/sm_make_chunk.c
> @@ -1367,10 +1367,14 @@ static struct sctp_chunk *_sctp_make_chu
> Â	sctp_chunkhdr_t *chunk_hdr;
> Â	struct sk_buff *skb;
> Â	struct sock *sk;
> +	int chunklen;
> +
> +	chunklen = sizeof(*chunk_hdr) + paylen;

I think this length still needs to be rounded up (with WORD_ROUND here,
instead of SCTP_PAD4 upstream).

Ben.

> +	if (chunklen > SCTP_MAX_CHUNK_LEN)
> +		goto nodata;
> Â
> Â	/* 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);
> Â	if (!skb)
> Â		goto nodata;
> Â
> 
> 
> 
-- 
Ben Hutchings
Software Developer, Codethink Ltd.