KASAN: use-after-free Read in __xfrm_state_lookup

[syzbot]

Hello,

syzkaller hit the following crash on
33ad61d0f799656e8987e9c80e6e15151bb857f3
git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next.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 __xfrm_state_lookup+0x695/0x6b0
net/xfrm/xfrm_state.c:833
Read of size 4 at addr ffff8801d434e538 by task syzkaller647520/2991

CPU: 1 PID: 2991 Comm: syzkaller647520 Not tainted 4.14.0-rc5+ #89
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
<IRQ>
__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_load4_noabort+0x14/0x20 mm/kasan/report.c:429
__xfrm_state_lookup+0x695/0x6b0 net/xfrm/xfrm_state.c:833
xfrm_state_lookup+0x8a/0x160 net/xfrm/xfrm_state.c:1592
xfrm_input+0x8e5/0x22f0 net/xfrm/xfrm_input.c:302
xfrm6_rcv_spi net/ipv6/xfrm6_input.c:30 [inline]
xfrm6_rcv_tnl+0x168/0x1d0 net/ipv6/xfrm6_input.c:64
xfrm6_rcv+0x17/0x20 net/ipv6/xfrm6_input.c:71
xfrm6_ah_rcv+0x166/0x300 net/ipv6/xfrm6_protocol.c:101
ip6_input_finish+0x36f/0x1700 net/ipv6/ip6_input.c:284
NF_HOOK include/linux/netfilter.h:249 [inline]
ip6_input+0xe9/0x560 net/ipv6/ip6_input.c:327
dst_input include/net/dst.h:465 [inline]
ip6_rcv_finish+0x1a9/0x7a0 net/ipv6/ip6_input.c:71
NF_HOOK include/linux/netfilter.h:249 [inline]
ipv6_rcv+0xf28/0x1f80 net/ipv6/ip6_input.c:208
__netif_receive_skb_core+0x1a3e/0x34b0 net/core/dev.c:4477
__netif_receive_skb+0x2c/0x1b0 net/core/dev.c:4542
process_backlog+0x203/0x740 net/core/dev.c:5221
napi_poll net/core/dev.c:5619 [inline]
net_rx_action+0x792/0x1910 net/core/dev.c:5685
__do_softirq+0x2d7/0xb85 kernel/softirq.c:284
do_softirq_own_stack+0x2a/0x40 arch/x86/entry/entry_64.S:957
</IRQ>
do_softirq.part.22+0x14d/0x190 kernel/softirq.c:328
do_softirq kernel/softirq.c:176 [inline]
__local_bh_enable_ip+0x135/0x160 kernel/softirq.c:181
local_bh_enable include/linux/bottom_half.h:31 [inline]
rcu_read_unlock_bh include/linux/rcupdate.h:727 [inline]
ip6_finish_output2+0xb26/0x22a0 net/ipv6/ip6_output.c:121
ip6_finish_output+0x2f9/0x920 net/ipv6/ip6_output.c:146
NF_HOOK_COND include/linux/netfilter.h:238 [inline]
ip6_output+0x1f4/0x850 net/ipv6/ip6_output.c:163
dst_output include/net/dst.h:459 [inline]
ip6_local_out+0x95/0x160 net/ipv6/output_core.c:176
ip6_send_skb+0xa1/0x330 net/ipv6/ip6_output.c:1658
ip6_push_pending_frames+0xb3/0xe0 net/ipv6/ip6_output.c:1678
rawv6_push_pending_frames net/ipv6/raw.c:616 [inline]
rawv6_sendmsg+0x2eb9/0x3e40 net/ipv6/raw.c:935
inet_sendmsg+0x11f/0x5e0 net/ipv4/af_inet.c:763
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
entry_SYSCALL_64_fastpath+0x1f/0xbe
RIP: 0033:0x4467c9
RSP: 002b:00007f93ea848cf8 EFLAGS: 00000212 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00000000004467c9
RDX: 00000000000007f1 RSI: 000000002013b7ff RDI: 0000000000000003
RBP: 0000000000000000 R08: 00000000204e8fe4 R09: 000000000000001c
R10: 0000000000000000 R11: 0000000000000212 R12: 0000000000000000
R13: 00007ffca6cb535f R14: 00007f93ea8499c0 R15: 0000000000000000

Allocated by task 2989:
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
__do_kmalloc_node mm/slab.c:3689 [inline]
__kmalloc_node_track_caller+0x47/0x70 mm/slab.c:3703
__kmalloc_reserve.isra.40+0x41/0xd0 net/core/skbuff.c:138
__alloc_skb+0x13b/0x780 net/core/skbuff.c:206
alloc_skb include/linux/skbuff.h:985 [inline]
sock_wmalloc+0x140/0x1d0 net/core/sock.c:1932
__ip6_append_data.isra.43+0x2681/0x3340 net/ipv6/ip6_output.c:1397
ip6_append_data+0x189/0x290 net/ipv6/ip6_output.c:1552
rawv6_sendmsg+0x1dd9/0x3e40 net/ipv6/raw.c:928
inet_sendmsg+0x11f/0x5e0 net/ipv4/af_inet.c:763
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
entry_SYSCALL_64_fastpath+0x1f/0xbe

Freed by task 2991:
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
skb_free_head+0x74/0xb0 net/core/skbuff.c:554
pskb_expand_head+0x36b/0x1210 net/core/skbuff.c:1494
__pskb_pull_tail+0x14a/0x17c0 net/core/skbuff.c:1877
pskb_may_pull include/linux/skbuff.h:2102 [inline]
xfrm_parse_spi+0x3d3/0x4d0 net/xfrm/xfrm_input.c:170
xfrm_input+0xce2/0x22f0 net/xfrm/xfrm_input.c:291
xfrm6_rcv_spi net/ipv6/xfrm6_input.c:30 [inline]
xfrm6_rcv_tnl+0x168/0x1d0 net/ipv6/xfrm6_input.c:64
xfrm6_rcv+0x17/0x20 net/ipv6/xfrm6_input.c:71
xfrm6_ah_rcv+0x166/0x300 net/ipv6/xfrm6_protocol.c:101
ip6_input_finish+0x36f/0x1700 net/ipv6/ip6_input.c:284
NF_HOOK include/linux/netfilter.h:249 [inline]
ip6_input+0xe9/0x560 net/ipv6/ip6_input.c:327
dst_input include/net/dst.h:465 [inline]
ip6_rcv_finish+0x1a9/0x7a0 net/ipv6/ip6_input.c:71
NF_HOOK include/linux/netfilter.h:249 [inline]
ipv6_rcv+0xf28/0x1f80 net/ipv6/ip6_input.c:208
__netif_receive_skb_core+0x1a3e/0x34b0 net/core/dev.c:4477
__netif_receive_skb+0x2c/0x1b0 net/core/dev.c:4542
process_backlog+0x203/0x740 net/core/dev.c:5221
napi_poll net/core/dev.c:5619 [inline]
net_rx_action+0x792/0x1910 net/core/dev.c:5685
__do_softirq+0x2d7/0xb85 kernel/softirq.c:284

The buggy address belongs to the object at ffff8801d434e500
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 56 bytes inside of
512-byte region [ffff8801d434e500, ffff8801d434e700)
The buggy address belongs to the page:
page:ffffea000750d380 count:1 mapcount:0 mapping:ffff8801d434e000 index:0x0


---
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[Florian Westphal]

syzbot reports:

BUG: KASAN: use-after-free in __xfrm_state_lookup+0x695/0x6b0

Read of size 4 at addr ffff8801d434e538 by task syzkaller647520/2991

[..]

__xfrm_state_lookup+0x695/0x6b0 net/xfrm/xfrm_state.c:833
xfrm_state_lookup+0x8a/0x160 net/xfrm/xfrm_state.c:1592
xfrm_input+0x8e5/0x22f0 net/xfrm/xfrm_input.c:302

The use-after-free is the ipv4 destination address, which points
to an skb head area that has been reallocated:

pskb_expand_head+0x36b/0x1210 net/core/skbuff.c:1494
__pskb_pull_tail+0x14a/0x17c0 net/core/skbuff.c:1877
pskb_may_pull include/linux/skbuff.h:2102 [inline]
xfrm_parse_spi+0x3d3/0x4d0 net/xfrm/xfrm_input.c:170
xfrm_input+0xce2/0x22f0 net/xfrm/xfrm_input.c:291

so the real bug is that xfrm_parse_spi() uses pskb_may_pull, but
for now do smaller workaround that makes xfrm_input fetch daddr
after spi parsing.

Reported-by: syzbot <syzk...@googlegroups.com>
Signed-off-by: Florian Westphal <f...@strlen.de>
---
net/xfrm/xfrm_input.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/xfrm/xfrm_input.c b/net/xfrm/xfrm_input.c
index 8ac9d32fb79d..1c6051cb7733 100644
--- a/net/xfrm/xfrm_input.c
+++ b/net/xfrm/xfrm_input.c
@@ -265,8 +265,6 @@ int xfrm_input(struct sk_buff *skb, int nexthdr, __be32 spi, int encap_type)
goto lock;
}

- daddr = (xfrm_address_t *)(skb_network_header(skb) +
- XFRM_SPI_SKB_CB(skb)->daddroff);
family = XFRM_SPI_SKB_CB(skb)->family;

/* if tunnel is present override skb->mark value with tunnel i_key */
@@ -293,6 +291,8 @@ int xfrm_input(struct sk_buff *skb, int nexthdr, __be32 spi, int encap_type)
goto drop;
}

+ daddr = (xfrm_address_t *)(skb_network_header(skb) +
+ XFRM_SPI_SKB_CB(skb)->daddroff);
do {
if (skb->sp->len == XFRM_MAX_DEPTH) {
XFRM_INC_STATS(net, LINUX_MIB_XFRMINBUFFERERROR);
--
2.13.6

[Steffen Klassert]

On Wed, Nov 01, 2017 at 08:30:49PM +0100, Florian Westphal wrote:
> syzbot reports:
> BUG: KASAN: use-after-free in __xfrm_state_lookup+0x695/0x6b0
> Read of size 4 at addr ffff8801d434e538 by task syzkaller647520/2991
> [..]
> __xfrm_state_lookup+0x695/0x6b0 net/xfrm/xfrm_state.c:833
> xfrm_state_lookup+0x8a/0x160 net/xfrm/xfrm_state.c:1592
> xfrm_input+0x8e5/0x22f0 net/xfrm/xfrm_input.c:302
>
> The use-after-free is the ipv4 destination address, which points
> to an skb head area that has been reallocated:
> pskb_expand_head+0x36b/0x1210 net/core/skbuff.c:1494
> __pskb_pull_tail+0x14a/0x17c0 net/core/skbuff.c:1877
> pskb_may_pull include/linux/skbuff.h:2102 [inline]
> xfrm_parse_spi+0x3d3/0x4d0 net/xfrm/xfrm_input.c:170
> xfrm_input+0xce2/0x22f0 net/xfrm/xfrm_input.c:291
>
> so the real bug is that xfrm_parse_spi() uses pskb_may_pull, but
> for now do smaller workaround that makes xfrm_input fetch daddr
> after spi parsing.
>
> Reported-by: syzbot <syzk...@googlegroups.com>
> Signed-off-by: Florian Westphal <f...@strlen.de>

Applied, thanks Florian!

[Eric Biggers]

[...]

> 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

Crash is no longer occurring, thanks Florian!

#syz fix: xfrm: defer daddr pointer assignment after spi parsing