From ecca8f88da5c4260cc2bccfefd2a24976704c366 Mon Sep 17 00:00:00 2001 From: Xin Long Date: Fri, 17 Nov 2017 14:11:11 +0800 Subject: sctp: set frag_point in sctp_setsockopt_maxseg correctly 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 Reported-by: Hangbin Liu Signed-off-by: Xin Long Acked-by: Marcelo Ricardo Leitner Signed-off-by: David S. Miller --- net/sctp/socket.c | 29 +++++++++++++++++++---------- 1 file changed, 19 insertions(+), 10 deletions(-) (limited to 'net') diff --git a/net/sctp/socket.c b/net/sctp/socket.c index 4c0a77292792..3204a9b29407 100644 --- a/net/sctp/socket.c +++ b/net/sctp/socket.c @@ -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(¶ms, 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; - asoc = sctp_id2assoc(sk, params.assoc_id); - if (!asoc && params.assoc_id && sctp_style(sk, UDP)) - return -EINVAL; + 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) { 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; } -- cgit