Re: sctp: skb_over_panic on INIT/INIT_ACK packet sending

[Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>]

Hi,

On Fri, Feb 09, 2018 at 02:38:59AM +0300, Alexey Kodanev wrote:
> Hi,
> 
> Got the following panic when the received INIT packet has a lot of
> address parameters, so that the INIT_ACK chunksize exceeds
> SCTP_MAX_CHUNK_LEN: 
> 
> [  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 may become too big, mostly
> because of the cookielen. Tried on local machine so both addrlen
> and cookielen was big: addrlen 39960 cookielen 80168.

Makes sense.

>  
> Not sure how to fix it correctly, may be we need a check here
> or add it to sctp_make_control()?

_sctp_make_chunk seems a good place for it, before trying to allocate
the skb. Any chunk bigger than SCTP_MAX_CHUNK_LEN is bogus and should
not be allowed.

> 
> diff --git a/net/sctp/sm_make_chunk.c b/net/sctp/sm_make_chunk.c
> index 793b05e..c27564c 100644
> --- a/net/sctp/sm_make_chunk.c
> +++ b/net/sctp/sm_make_chunk.c
> @@ -475,6 +475,9 @@ struct sctp_chunk *sctp_make_init_ack(const struct sctp_association *asoc,
>         if (num_ext)
>                 chunksize += SCTP_PAD4(sizeof(ext_param) + num_ext);
>  
> +       if (chunksize > SCTP_MAX_CHUNK_LEN)
> +               goto nomem_chunk;
> +
>         /* Now allocate and fill out the chunk.  */
>         retval = sctp_make_control(asoc, SCTP_CID_INIT_ACK, 0, chunksize, gfp);
>         if (!retval)
> 
> And for INIT as well...
> 
> Otherwise this chunk goes to skb_packet_transmit() -> sctp_packet_pack()
> where panic on
> 
>   skb_put_data(nskb, chunk->skb->data, chunk->skb->len);
> 
> nskb (head skb) was previously allocated with packet->size that looks
> like getting the chunk size from u16 chunk_hdr->length.

Huh, yes.

Thanks,
Marcelo

> 
> Thanks,
> Alexey
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