This is a note to let you know that I've just added the patch titled
sctp: set frag_point in sctp_setsockopt_maxseg correctly
to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: sctp-set-frag_point-in-sctp_setsockopt_maxseg-correctly.patch and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From ecca8f88da5c4260cc2bccfefd2a24976704c366 Mon Sep 17 00:00:00 2001
From: Xin Long lucien.xin@gmail.com Date: Fri, 17 Nov 2017 14:11:11 +0800 Subject: sctp: set frag_point in sctp_setsockopt_maxseg correctly
From: Xin Long lucien.xin@gmail.com
commit ecca8f88da5c4260cc2bccfefd2a24976704c366 upstream.
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- include/net/sctp/sctp.h | 3 ++- net/sctp/socket.c | 29 +++++++++++++++++++---------- 2 files changed, 21 insertions(+), 11 deletions(-)
--- a/include/net/sctp/sctp.h +++ b/include/net/sctp/sctp.h @@ -433,7 +433,8 @@ static inline int sctp_frag_point(const 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; } --- a/net/sctp/socket.c +++ b/net/sctp/socket.c @@ -3125,9 +3125,9 @@ static int sctp_setsockopt_mappedv4(stru */ 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)) { @@ -3143,26 +3143,35 @@ static int sctp_setsockopt_maxseg(struct 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; }
Patches currently in stable-queue which might be from lucien.xin@gmail.com are
queue-4.9/sctp-set-frag_point-in-sctp_setsockopt_maxseg-correctly.patch