KASAN: use-after-free Read in sctp_association_free

[syzbot]

Hello,

syzkaller hit the following crash on
25a5d23b47994cdb451dcd2bc8ac310a1492f71b
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/master
compiler: gcc (GCC) 7.1.1 20170620
.config is attached
Raw console output is attached.
C reproducer is attached
syzkaller reproducer is attached. See https://goo.gl/kgGztJ
for information about syzkaller reproducers


==================================================================
BUG: KASAN: use-after-free in sctp_association_free+0x7b7/0x930
net/sctp/associola.c:333
Read of size 8 at addr ffff8801d21d4720 by task syzkaller504854/3007

CPU: 0 PID: 3007 Comm: syzkaller504854 Not tainted 4.14.0-rc6+ #62
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:16 [inline]
dump_stack+0x194/0x257 lib/dump_stack.c:52
print_address_description+0x73/0x250 mm/kasan/report.c:252
kasan_report_error mm/kasan/report.c:351 [inline]
kasan_report+0x25b/0x340 mm/kasan/report.c:409
__asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:430
sctp_association_free+0x7b7/0x930 net/sctp/associola.c:333
sctp_sendmsg+0x2311/0x31f0 net/sctp/socket.c:2011
inet_sendmsg+0x11f/0x5e0 net/ipv4/af_inet.c:762
sock_sendmsg_nosec net/socket.c:633 [inline]
sock_sendmsg+0xca/0x110 net/socket.c:643
SYSC_sendto+0x352/0x5a0 net/socket.c:1750
SyS_sendto+0x40/0x50 net/socket.c:1718
do_syscall_32_irqs_on arch/x86/entry/common.c:329 [inline]
do_fast_syscall_32+0x3f2/0xf05 arch/x86/entry/common.c:391
entry_SYSENTER_compat+0x51/0x60 arch/x86/entry/entry_64_compat.S:124
RIP: 0023:0xf7fd2c79
RSP: 002b:00000000f5fca1ec EFLAGS: 00000292 ORIG_RAX: 0000000000000171
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000020925000
RDX: 0000000000000002 RSI: 0000000000000000 RDI: 00000000209e1000
RBP: 000000000000001c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 3007:
save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
save_stack+0x43/0xd0 mm/kasan/kasan.c:447
set_track mm/kasan/kasan.c:459 [inline]
kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:551
kmem_cache_alloc_trace+0x136/0x750 mm/slab.c:3627
kmalloc include/linux/slab.h:493 [inline]
kzalloc include/linux/slab.h:666 [inline]
sctp_association_new+0x114/0x21e0 net/sctp/associola.c:309
sctp_sendmsg+0x128c/0x31f0 net/sctp/socket.c:1838
inet_sendmsg+0x11f/0x5e0 net/ipv4/af_inet.c:762
sock_sendmsg_nosec net/socket.c:633 [inline]
sock_sendmsg+0xca/0x110 net/socket.c:643
SYSC_sendto+0x352/0x5a0 net/socket.c:1750
SyS_sendto+0x40/0x50 net/socket.c:1718
do_syscall_32_irqs_on arch/x86/entry/common.c:329 [inline]
do_fast_syscall_32+0x3f2/0xf05 arch/x86/entry/common.c:391
entry_SYSENTER_compat+0x51/0x60 arch/x86/entry/entry_64_compat.S:124

Freed by task 3007:
save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
save_stack+0x43/0xd0 mm/kasan/kasan.c:447
set_track mm/kasan/kasan.c:459 [inline]
kasan_slab_free+0x71/0xc0 mm/kasan/kasan.c:524
__cache_free mm/slab.c:3503 [inline]
kfree+0xca/0x250 mm/slab.c:3820
sctp_association_destroy net/sctp/associola.c:435 [inline]
sctp_association_put+0x21c/0x2f0 net/sctp/associola.c:884
sctp_wait_for_sndbuf+0x5e3/0x7c0 net/sctp/socket.c:7836
sctp_sendmsg+0x2750/0x31f0 net/sctp/socket.c:1935
inet_sendmsg+0x11f/0x5e0 net/ipv4/af_inet.c:762
sock_sendmsg_nosec net/socket.c:633 [inline]
sock_sendmsg+0xca/0x110 net/socket.c:643
SYSC_sendto+0x352/0x5a0 net/socket.c:1750
SyS_sendto+0x40/0x50 net/socket.c:1718
do_syscall_32_irqs_on arch/x86/entry/common.c:329 [inline]
do_fast_syscall_32+0x3f2/0xf05 arch/x86/entry/common.c:391
entry_SYSENTER_compat+0x51/0x60 arch/x86/entry/entry_64_compat.S:124

The buggy address belongs to the object at ffff8801d21d4700
which belongs to the cache kmalloc-4096 of size 4096
The buggy address is located 32 bytes inside of
4096-byte region [ffff8801d21d4700, ffff8801d21d5700)
The buggy address belongs to the page:
page:ffffea0007487500 count:1 mapcount:0 mapping:ffff8801d21d4700 index:0x0
compound_mapcount: 0
flags: 0x200000000008100(slab|head)
raw: 0200000000008100 ffff8801d21d4700 0000000000000000 0000000100000001
raw: ffffea0007487420 ffff8801dac01a48 ffff8801dac00dc0 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801d21d4600: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8801d21d4680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff8801d21d4700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8801d21d4780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801d21d4800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
This bug is generated by a dumb bot. It may contain errors.
See https://goo.gl/tpsmEJ for details.
Direct all questions to syzk...@googlegroups.com.
Please credit me with: Reported-by: syzbot <syzk...@googlegroups.com>

syzbot will keep track of this bug report.
Once a fix for this bug is committed, please reply to this email with:
#syz fix: exact-commit-title
To mark this as a duplicate of another syzbot report, please reply with:
#syz dup: exact-subject-of-another-report
If it's a one-off invalid bug report, please reply with:
#syz invalid
Note: if the crash happens again, it will cause creation of a new bug
report.
Note: all commands must start from beginning of the line.

[Xin Long]

On Thu, Nov 2, 2017 at 1:55 AM, syzbot
<bot+df9412138a14678abd...@syzkaller.appspotmail.com>
wrote:

asoc could have been freed by sctp_stop_t1_and_abort or elsewhere
when waiting for buf without holding sk lock.

One possible fix:

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index c75acdf..e2ea12a 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -2015,7 +2015,7 @@ static int sctp_sendmsg(struct sock *sk, struct
msghdr *msg, size_t msg_len)
goto out_unlock;

out_free:
- if (new_asoc)
+ if (new_asoc && err != -ESRCH)
sctp_association_free(asoc);
out_unlock:
release_sock(sk);
@@ -7976,10 +7976,11 @@ static int sctp_wait_for_sndbuf(struct
sctp_association *asoc, long *timeo_p,
for (;;) {
prepare_to_wait_exclusive(&asoc->wait, &wait,
TASK_INTERRUPTIBLE);
+ if (asoc->base.dead)
+ goto do_dead;
if (!*timeo_p)
goto do_nonblock;
- if (sk->sk_err || asoc->state >= SCTP_STATE_SHUTDOWN_PENDING ||
- asoc->base.dead)
+ if (sk->sk_err || asoc->state >= SCTP_STATE_SHUTDOWN_PENDING)
goto do_error;
if (signal_pending(current))
goto do_interrupted;
@@ -8004,6 +8005,10 @@ static int sctp_wait_for_sndbuf(struct
sctp_association *asoc, long *timeo_p,

return err;

+do_dead:
+ err = -ESRCH;
+ goto out;
+
do_error:
err = -EPIPE;
goto out;

will check for sure before posting. thanks.

[Eric Biggers]

This crash has stopped occurring. I assume it was fixed by commit ca3af4dd28cff
(thanks Xin!), so let's tell syzbot so that it can continue to report crashes in
the same place:

#syz fix: sctp: do not free asoc when it is already dead in sctp_sendmsg

- Eric