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sctp: frag_point sanity check

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If for some reason an association's fragmentation point is zero,
sctp_datamsg_from_user will try to endlessly try to divide a message
into zero-sized chunks. This eventually causes kernel panic due to
running out of memory.

Although this situation is quite unlikely, it has occurred before as
reported. I propose to add this simple last-ditch sanity check due to
the severity of the potential consequences.

Signed-off-by: Jakub Audykowicz <jakub.audykowicz@gmail.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jakub Audykowicz 2018-12-04 20:27:41 +01:00 committed by David S. Miller
parent b2b7af8611
commit afd0a8006e
3 changed files with 12 additions and 2 deletions
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5
include/net/sctp/sctp.h
View File

@ -620,4 +620,9 @@ static inline bool sctp_transport_pmtu_check(struct sctp_transport *t)
return false;
}
static inline __u32 sctp_min_frag_point(struct sctp_sock *sp, __u16 datasize)
{
return sctp_mtu_payload(sp, SCTP_DEFAULT_MINSEGMENT, datasize);
}
#endif /* __net_sctp_h__ */

6
net/sctp/chunk.c
View File

@ -191,6 +191,12 @@ struct sctp_datamsg *sctp_datamsg_from_user(struct sctp_association *asoc,
* the packet
*/
max_data = asoc->frag_point;
if (unlikely(!max_data)) {
max_data = sctp_min_frag_point(sctp_sk(asoc->base.sk),
sctp_datachk_len(&asoc->stream));
pr_warn_ratelimited("%s: asoc:%p frag_point is zero, forcing max_data to default minimum (%Zu)",
__func__, asoc, max_data);
}
/* If the the peer requested that we authenticate DATA chunks
* we need to account for bundling of the AUTH chunks along with

3
net/sctp/socket.c
View File

@ -3324,8 +3324,7 @@ static int sctp_setsockopt_maxseg(struct sock *sk, char __user *optval, unsigned
__u16 datasize = asoc ? sctp_datachk_len(&asoc->stream) :
sizeof(struct sctp_data_chunk);
min_len = sctp_mtu_payload(sp, SCTP_DEFAULT_MINSEGMENT,
datasize);
min_len = sctp_min_frag_point(sp, datasize);
max_len = SCTP_MAX_CHUNK_LEN - datasize;
if (val < min_len || val > max_len)