3.16.72-rc1 review patch. If anyone has any objections, please let me know.
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From: Eric Dumazet edumazet@google.com
commit a622b40035d16196bf19b2b33b854862595245fc upstream.
Before taking a refcount on a rcu protected structure, we need to make sure the refcount is not zero.
syzbot reported :
refcount_t: increment on 0; use-after-free. WARNING: CPU: 1 PID: 23533 at lib/refcount.c:156 refcount_inc_checked lib/refcount.c:156 [inline] WARNING: CPU: 1 PID: 23533 at lib/refcount.c:156 refcount_inc_checked+0x61/0x70 lib/refcount.c:154 Kernel panic - not syncing: panic_on_warn set ... CPU: 1 PID: 23533 Comm: syz-executor.2 Not tainted 5.1.0-rc7+ #93 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+0x172/0x1f0 lib/dump_stack.c:113 panic+0x2cb/0x65c kernel/panic.c:214 __warn.cold+0x20/0x45 kernel/panic.c:571 report_bug+0x263/0x2b0 lib/bug.c:186 fixup_bug arch/x86/kernel/traps.c:179 [inline] fixup_bug arch/x86/kernel/traps.c:174 [inline] do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:272 do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:291 invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:973 RIP: 0010:refcount_inc_checked lib/refcount.c:156 [inline] RIP: 0010:refcount_inc_checked+0x61/0x70 lib/refcount.c:154 Code: 1d 98 2b 2a 06 31 ff 89 de e8 db 2c 40 fe 84 db 75 dd e8 92 2b 40 fe 48 c7 c7 20 7a a1 87 c6 05 78 2b 2a 06 01 e8 7d d9 12 fe <0f> 0b eb c1 90 90 90 90 90 90 90 90 90 90 90 55 48 89 e5 41 57 41 RSP: 0018:ffff888069f0fba8 EFLAGS: 00010286 RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 RDX: 000000000000f353 RSI: ffffffff815afcb6 RDI: ffffed100d3e1f67 RBP: ffff888069f0fbb8 R08: ffff88809b1845c0 R09: ffffed1015d23ef1 R10: ffffed1015d23ef0 R11: ffff8880ae91f787 R12: ffff8880a8f26968 R13: 0000000000000004 R14: dffffc0000000000 R15: ffff8880a49a6440 l2tp_tunnel_inc_refcount net/l2tp/l2tp_core.h:240 [inline] l2tp_tunnel_get+0x250/0x580 net/l2tp/l2tp_core.c:173 pppol2tp_connect+0xc00/0x1c70 net/l2tp/l2tp_ppp.c:702 __sys_connect+0x266/0x330 net/socket.c:1808 __do_sys_connect net/socket.c:1819 [inline] __se_sys_connect net/socket.c:1816 [inline] __x64_sys_connect+0x73/0xb0 net/socket.c:1816
Fixes: 54652eb12c1b ("l2tp: hold tunnel while looking up sessions in l2tp_netlink") Signed-off-by: Eric Dumazet edumazet@google.com Reported-by: syzbot syzkaller@googlegroups.com Cc: Guillaume Nault g.nault@alphalink.fr Signed-off-by: David S. Miller davem@davemloft.net [bwh: Backported to 3.16: use atomic not refcount API] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- net/l2tp/l2tp_core.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
--- a/net/l2tp/l2tp_core.c +++ b/net/l2tp/l2tp_core.c @@ -217,8 +217,8 @@ struct l2tp_tunnel *l2tp_tunnel_get(cons
rcu_read_lock_bh(); list_for_each_entry_rcu(tunnel, &pn->l2tp_tunnel_list, list) { - if (tunnel->tunnel_id == tunnel_id) { - l2tp_tunnel_inc_refcount(tunnel); + if (tunnel->tunnel_id == tunnel_id && + atomic_inc_not_zero(&tunnel->ref_count)) { rcu_read_unlock_bh();
return tunnel; @@ -238,8 +238,8 @@ struct l2tp_tunnel *l2tp_tunnel_get_nth(
rcu_read_lock_bh(); list_for_each_entry_rcu(tunnel, &pn->l2tp_tunnel_list, list) { - if (++count > nth) { - l2tp_tunnel_inc_refcount(tunnel); + if (++count > nth && + atomic_inc_not_zero(&tunnel->ref_count)) { rcu_read_unlock_bh(); return tunnel; }