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sctp: set frag_point in sctp_setsockopt_maxseg correctly

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Now in sctp_setsockopt_maxseg user_frag or frag_point can be set with
val >= 8 and val <= SCTP_MAX_CHUNK_LEN. But both checks are incorrect.

val >= 8 means frag_point can even be less than SCTP_DEFAULT_MINSEGMENT.
Then in sctp_datamsg_from_user(), when it's value is greater than cookie
echo len and trying to bundle with cookie echo chunk, the first_len will
overflow.

The worse case is when it's value is equal as cookie echo len, first_len
becomes 0, it will go into a dead loop for fragment later on. In Hangbin
syzkaller testing env, oom was even triggered due to consecutive memory
allocation in that loop.

Besides, SCTP_MAX_CHUNK_LEN is the max size of the whole chunk, it should
deduct the data header for frag_point or user_frag check.

This patch does a proper check with SCTP_DEFAULT_MINSEGMENT subtracting
the sctphdr and datahdr, SCTP_MAX_CHUNK_LEN subtracting datahdr when
setting frag_point via sockopt. It also improves sctp_setsockopt_maxseg
codes.

Suggested-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Reported-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Xin Long 2017-11-17 14:11:11 +08:00 committed by David S. Miller
parent d35ef8f846
commit ecca8f88da
2 changed files with 21 additions and 11 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

3
include/net/sctp/sctp.h
View file

@ -444,7 +444,8 @@ static inline int sctp_frag_point(const struct sctp_association *asoc, int pmtu)
if (asoc->user_frag)
frag = min_t(int, frag, asoc->user_frag);
frag = SCTP_TRUNC4(min_t(int, frag, SCTP_MAX_CHUNK_LEN));
frag = SCTP_TRUNC4(min_t(int, frag, SCTP_MAX_CHUNK_LEN -
sizeof(struct sctp_data_chunk)));
return frag;
}

29
net/sctp/socket.c
View file

@ -3140,9 +3140,9 @@ static int sctp_setsockopt_mappedv4(struct sock *sk, char __user *optval, unsign
*/
static int sctp_setsockopt_maxseg(struct sock *sk, char __user *optval, unsigned int optlen)
{
struct sctp_sock *sp = sctp_sk(sk);
struct sctp_assoc_value params;
struct sctp_association *asoc;
struct sctp_sock *sp = sctp_sk(sk);
int val;
if (optlen == sizeof(int)) {
@ -3158,26 +3158,35 @@ static int sctp_setsockopt_maxseg(struct sock *sk, char __user *optval, unsigned
if (copy_from_user(&params, optval, optlen))
return -EFAULT;
val = params.assoc_value;
} else
} else {
return -EINVAL;
}
if ((val != 0) && ((val < 8) || (val > SCTP_MAX_CHUNK_LEN)))
return -EINVAL;
if (val) {
int min_len, max_len;
min_len = SCTP_DEFAULT_MINSEGMENT - sp->pf->af->net_header_len;
min_len -= sizeof(struct sctphdr) +
sizeof(struct sctp_data_chunk);
max_len = SCTP_MAX_CHUNK_LEN - sizeof(struct sctp_data_chunk);
if (val < min_len || val > max_len)
return -EINVAL;
}
asoc = sctp_id2assoc(sk, params.assoc_id);
if (!asoc && params.assoc_id && sctp_style(sk, UDP))
return -EINVAL;
if (asoc) {
if (val == 0) {
val = asoc->pathmtu;
val -= sp->pf->af->net_header_len;
val = asoc->pathmtu - sp->pf->af->net_header_len;
val -= sizeof(struct sctphdr) +
sizeof(struct sctp_data_chunk);
sizeof(struct sctp_data_chunk);
}
asoc->user_frag = val;
asoc->frag_point = sctp_frag_point(asoc, asoc->pathmtu);
} else {
if (params.assoc_id && sctp_style(sk, UDP))
return -EINVAL;
sp->user_frag = val;
}