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Subject[PATCH 4.9 136/171] ipv6: mcast: fix a use-after-free in inet6_mc_check
4.9-stable review patch.  If anyone has any objections, please let me know.


From: Eric Dumazet <>

[ Upstream commit dc012f3628eaecfb5ba68404a5c30ef501daf63d ]

syzbot found a use-after-free in inet6_mc_check [1]

The problem here is that inet6_mc_check() uses rcu
and read_lock(&iml->sflock)

So the fact that ip6_mc_leave_src() is called under RTNL
and the socket lock does not help us, we need to acquire
iml->sflock in write mode.

In the future, we should convert all this stuff to RCU.

BUG: KASAN: use-after-free in ipv6_addr_equal include/net/ipv6.h:521 [inline]
BUG: KASAN: use-after-free in inet6_mc_check+0xae7/0xb40 net/ipv6/mcast.c:649
Read of size 8 at addr ffff8801ce7f2510 by task syz-executor0/22432

CPU: 1 PID: 22432 Comm: syz-executor0 Not tainted 4.19.0-rc7+ #280
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x1c4/0x2b4 lib/dump_stack.c:113
print_address_description.cold.8+0x9/0x1ff mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report.cold.9+0x242/0x309 mm/kasan/report.c:412
__asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
ipv6_addr_equal include/net/ipv6.h:521 [inline]
inet6_mc_check+0xae7/0xb40 net/ipv6/mcast.c:649
__raw_v6_lookup+0x320/0x3f0 net/ipv6/raw.c:98
ipv6_raw_deliver net/ipv6/raw.c:183 [inline]
raw6_local_deliver+0x3d3/0xcb0 net/ipv6/raw.c:240
ip6_input_finish+0x467/0x1aa0 net/ipv6/ip6_input.c:345
NF_HOOK include/linux/netfilter.h:289 [inline]
ip6_input+0xe9/0x600 net/ipv6/ip6_input.c:426
ip6_mc_input+0x48a/0xd20 net/ipv6/ip6_input.c:503
dst_input include/net/dst.h:450 [inline]
ip6_rcv_finish+0x17a/0x330 net/ipv6/ip6_input.c:76
NF_HOOK include/linux/netfilter.h:289 [inline]
ipv6_rcv+0x120/0x640 net/ipv6/ip6_input.c:271
__netif_receive_skb_one_core+0x14d/0x200 net/core/dev.c:4913
__netif_receive_skb+0x2c/0x1e0 net/core/dev.c:5023
netif_receive_skb_internal+0x12c/0x620 net/core/dev.c:5126
napi_frags_finish net/core/dev.c:5664 [inline]
napi_gro_frags+0x75a/0xc90 net/core/dev.c:5737
tun_get_user+0x3189/0x4250 drivers/net/tun.c:1923
tun_chr_write_iter+0xb9/0x154 drivers/net/tun.c:1968
call_write_iter include/linux/fs.h:1808 [inline]
do_iter_readv_writev+0x8b0/0xa80 fs/read_write.c:680
do_iter_write+0x185/0x5f0 fs/read_write.c:959
vfs_writev+0x1f1/0x360 fs/read_write.c:1004
do_writev+0x11a/0x310 fs/read_write.c:1039
__do_sys_writev fs/read_write.c:1112 [inline]
__se_sys_writev fs/read_write.c:1109 [inline]
__x64_sys_writev+0x75/0xb0 fs/read_write.c:1109
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
RIP: 0033:0x457421
Code: 75 14 b8 14 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 34 b5 fb ff c3 48 83 ec 08 e8 1a 2d 00 00 48 89 04 24 b8 14 00 00 00 0f 05 <48> 8b 3c 24 48 89 c2 e8 63 2d 00 00 48 89 d0 48 83 c4 08 48 3d 01
RSP: 002b:00007f2d30ecaba0 EFLAGS: 00000293 ORIG_RAX: 0000000000000014
RAX: ffffffffffffffda RBX: 000000000000003e RCX: 0000000000457421
RDX: 0000000000000001 RSI: 00007f2d30ecabf0 RDI: 00000000000000f0
RBP: 0000000020000500 R08: 00000000000000f0 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000293 R12: 00007f2d30ecb6d4
R13: 00000000004c4890 R14: 00000000004d7b90 R15: 00000000ffffffff

Allocated by task 22437:
save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:553
__do_kmalloc mm/slab.c:3718 [inline]
__kmalloc+0x14e/0x760 mm/slab.c:3727
kmalloc include/linux/slab.h:518 [inline]
sock_kmalloc+0x15a/0x1f0 net/core/sock.c:1983
ip6_mc_source+0x14dd/0x1960 net/ipv6/mcast.c:427
do_ipv6_setsockopt.isra.9+0x3afb/0x45d0 net/ipv6/ipv6_sockglue.c:743
ipv6_setsockopt+0xbd/0x170 net/ipv6/ipv6_sockglue.c:933
rawv6_setsockopt+0x59/0x140 net/ipv6/raw.c:1069
sock_common_setsockopt+0x9a/0xe0 net/core/sock.c:3038
__sys_setsockopt+0x1ba/0x3c0 net/socket.c:1902
__do_sys_setsockopt net/socket.c:1913 [inline]
__se_sys_setsockopt net/socket.c:1910 [inline]
__x64_sys_setsockopt+0xbe/0x150 net/socket.c:1910
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290

Freed by task 22430:
save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/kasan.c:521
kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
__cache_free mm/slab.c:3498 [inline]
kfree+0xcf/0x230 mm/slab.c:3813
__sock_kfree_s net/core/sock.c:2004 [inline]
sock_kfree_s+0x29/0x60 net/core/sock.c:2010
ip6_mc_leave_src+0x11a/0x1d0 net/ipv6/mcast.c:2448
__ipv6_sock_mc_close+0x20b/0x4e0 net/ipv6/mcast.c:310
ipv6_sock_mc_close+0x158/0x1d0 net/ipv6/mcast.c:328
inet6_release+0x40/0x70 net/ipv6/af_inet6.c:452
__sock_release+0xd7/0x250 net/socket.c:579
sock_close+0x19/0x20 net/socket.c:1141
__fput+0x385/0xa30 fs/file_table.c:278
____fput+0x15/0x20 fs/file_table.c:309
task_work_run+0x1e8/0x2a0 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:193 [inline]
exit_to_usermode_loop+0x318/0x380 arch/x86/entry/common.c:166
prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
do_syscall_64+0x6be/0x820 arch/x86/entry/common.c:293

The buggy address belongs to the object at ffff8801ce7f2500
which belongs to the cache kmalloc-192 of size 192
The buggy address is located 16 bytes inside of
192-byte region [ffff8801ce7f2500, ffff8801ce7f25c0)
The buggy address belongs to the page:
page:ffffea000739fc80 count:1 mapcount:0 mapping:ffff8801da800040 index:0x0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffffea0006f6e548 ffffea000737b948 ffff8801da800040
raw: 0000000000000000 ffff8801ce7f2000 0000000100000010 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801ce7f2400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801ce7f2480: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>ffff8801ce7f2500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801ce7f2580: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
ffff8801ce7f2600: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

Signed-off-by: Eric Dumazet <>
Reported-by: syzbot <>
Signed-off-by: David S. Miller <>
Signed-off-by: Greg Kroah-Hartman <>
net/ipv6/mcast.c | 16 ++++++++--------
1 file changed, 8 insertions(+), 8 deletions(-)

--- a/net/ipv6/mcast.c
+++ b/net/ipv6/mcast.c
@@ -2413,17 +2413,17 @@ static int ip6_mc_leave_src(struct sock
int err;

- /* callers have the socket lock and rtnl lock
- * so no other readers or writers of iml or its sflist
- */
+ write_lock_bh(&iml->sflock);
if (!iml->sflist) {
/* any-source empty exclude case */
- return ip6_mc_del_src(idev, &iml->addr, iml->sfmode, 0, NULL, 0);
+ err = ip6_mc_del_src(idev, &iml->addr, iml->sfmode, 0, NULL, 0);
+ } else {
+ err = ip6_mc_del_src(idev, &iml->addr, iml->sfmode,
+ iml->sflist->sl_count, iml->sflist->sl_addr, 0);
+ sock_kfree_s(sk, iml->sflist, IP6_SFLSIZE(iml->sflist->sl_max));
+ iml->sflist = NULL;
- err = ip6_mc_del_src(idev, &iml->addr, iml->sfmode,
- iml->sflist->sl_count, iml->sflist->sl_addr, 0);
- sock_kfree_s(sk, iml->sflist, IP6_SFLSIZE(iml->sflist->sl_max));
- iml->sflist = NULL;
+ write_unlock_bh(&iml->sflock);
return err;

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