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Subject[PATCH 4.4 171/190] pptp: remove a buggy dst release in pptp_connect()
Date
4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@google.com>


[ Upstream commit bfacfb457b36911a10140b8cb3ce76a74883ac5a ]

Once dst has been cached in socket via sk_setup_caps(),
it is illegal to call ip_rt_put() (or dst_release()),
since sk_setup_caps() did not change dst refcount.

We can still dereference it since we hold socket lock.

Caugth by syzbot :

BUG: KASAN: use-after-free in atomic_dec_return include/asm-generic/atomic-instrumented.h:198 [inline]
BUG: KASAN: use-after-free in dst_release+0x27/0xa0 net/core/dst.c:185
Write of size 4 at addr ffff8801c54dc040 by task syz-executor4/20088

CPU: 1 PID: 20088 Comm: syz-executor4 Not tainted 4.16.0+ #376
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x1a7/0x27d lib/dump_stack.c:53
print_address_description+0x73/0x250 mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report+0x23c/0x360 mm/kasan/report.c:412
check_memory_region_inline mm/kasan/kasan.c:260 [inline]
check_memory_region+0x137/0x190 mm/kasan/kasan.c:267
kasan_check_write+0x14/0x20 mm/kasan/kasan.c:278
atomic_dec_return include/asm-generic/atomic-instrumented.h:198 [inline]
dst_release+0x27/0xa0 net/core/dst.c:185
sk_dst_set include/net/sock.h:1812 [inline]
sk_dst_reset include/net/sock.h:1824 [inline]
sock_setbindtodevice net/core/sock.c:610 [inline]
sock_setsockopt+0x431/0x1b20 net/core/sock.c:707
SYSC_setsockopt net/socket.c:1845 [inline]
SyS_setsockopt+0x2ff/0x360 net/socket.c:1828
do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x4552d9
RSP: 002b:00007f4878126c68 EFLAGS: 00000246 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 00007f48781276d4 RCX: 00000000004552d9
RDX: 0000000000000019 RSI: 0000000000000001 RDI: 0000000000000013
RBP: 000000000072bea0 R08: 0000000000000010 R09: 0000000000000000
R10: 00000000200010c0 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000526 R14: 00000000006fac30 R15: 0000000000000000

Allocated by task 20088:
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:552
kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:489
kmem_cache_alloc+0x12e/0x760 mm/slab.c:3542
dst_alloc+0x11f/0x1a0 net/core/dst.c:104
rt_dst_alloc+0xe9/0x540 net/ipv4/route.c:1520
__mkroute_output net/ipv4/route.c:2265 [inline]
ip_route_output_key_hash_rcu+0xa49/0x2c60 net/ipv4/route.c:2493
ip_route_output_key_hash+0x20b/0x370 net/ipv4/route.c:2322
__ip_route_output_key include/net/route.h:126 [inline]
ip_route_output_flow+0x26/0xa0 net/ipv4/route.c:2577
ip_route_output_ports include/net/route.h:163 [inline]
pptp_connect+0xa84/0x1170 drivers/net/ppp/pptp.c:453
SYSC_connect+0x213/0x4a0 net/socket.c:1639
SyS_connect+0x24/0x30 net/socket.c:1620
do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
entry_SYSCALL_64_after_hwframe+0x42/0xb7

Freed by task 20082:
save_stack+0x43/0xd0 mm/kasan/kasan.c:447
set_track mm/kasan/kasan.c:459 [inline]
__kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:520
kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:527
__cache_free mm/slab.c:3486 [inline]
kmem_cache_free+0x83/0x2a0 mm/slab.c:3744
dst_destroy+0x266/0x380 net/core/dst.c:140
dst_destroy_rcu+0x16/0x20 net/core/dst.c:153
__rcu_reclaim kernel/rcu/rcu.h:178 [inline]
rcu_do_batch kernel/rcu/tree.c:2675 [inline]
invoke_rcu_callbacks kernel/rcu/tree.c:2930 [inline]
__rcu_process_callbacks kernel/rcu/tree.c:2897 [inline]
rcu_process_callbacks+0xd6c/0x17b0 kernel/rcu/tree.c:2914
__do_softirq+0x2d7/0xb85 kernel/softirq.c:285

The buggy address belongs to the object at ffff8801c54dc000
which belongs to the cache ip_dst_cache of size 168
The buggy address is located 64 bytes inside of
168-byte region [ffff8801c54dc000, ffff8801c54dc0a8)
The buggy address belongs to the page:
page:ffffea0007153700 count:1 mapcount:0 mapping:ffff8801c54dc000 index:0x0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffff8801c54dc000 0000000000000000 0000000100000010
raw: ffffea0006b34b20 ffffea0006b6c1e0 ffff8801d674a1c0 0000000000000000
page dumped because: kasan: bad access detected

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/net/ppp/pptp.c | 1 -
1 file changed, 1 deletion(-)

--- a/drivers/net/ppp/pptp.c
+++ b/drivers/net/ppp/pptp.c
@@ -501,7 +501,6 @@ static int pptp_connect(struct socket *s
po->chan.mtu = dst_mtu(&rt->dst);
if (!po->chan.mtu)
po->chan.mtu = PPP_MRU;
- ip_rt_put(rt);
po->chan.mtu -= PPTP_HEADER_OVERHEAD;

po->chan.hdrlen = 2 + sizeof(struct pptp_gre_header);

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