On Mon, Mar 18, 2019 at 4:49 AM syzbot
[off-list ref] wrote:

syzbot has bisected this bug to:

commit c981f254cc82f50f8cb864ce6432097b23195b9c
Author: Al Viro [off-list ref]
Date:   Sun Jan 7 18:19:09 2018 +0000

     sctp: use vmemdup_user() rather than badly open-coding memdup_user()

'addrs_size' is passed from users, we actually used GFP_USER to
put some more restrictions on it in this commit:

commit cacc06215271104b40773c99547c506095db6ad4
Author: Marcelo Ricardo Leitner [off-list ref]
Date:   Mon Nov 30 14:32:54 2015 -0200

    sctp: use GFP_USER for user-controlled kmalloc

However, vmemdup_user() will 'ignore' this flag when going to vmalloc_*(),
So we probably should fix it by using memdup_user() to avoid that
open-coding part instead:

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index ea95cd4..e5bcade 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c

@@ -999,7 +999,7 @@ static int sctp_setsockopt_bindx(struct sock *sk,
        if (unlikely(addrs_size <= 0))
                return -EINVAL;

-       kaddrs = vmemdup_user(addrs, addrs_size);
+       kaddrs = memdup_user(addrs, addrs_size);

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=137bcecf200000
start commit:   c981f254 sctp: use vmemdup_user() rather than badly open-c..
git tree:       upstream
final crash:    https://syzkaller.appspot.com/x/report.txt?x=10fbcecf200000
console output: https://syzkaller.appspot.com/x/log.txt?x=177bcecf200000
kernel config:  https://syzkaller.appspot.com/x/.config?x=5e7dc790609552d7
dashboard link: https://syzkaller.appspot.com/bug?extid=ec1b7575afef85a0e5ca
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16a9a84b400000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17199bb3400000

Reported-by: syzbot+ec1b7575afef85a0e5ca@syzkaller.appspotmail.com
Fixes: c981f254 ("sctp: use vmemdup_user() rather than badly open-coding
memdup_user()")