KASAN: slab-out-of-bounds Read in _decode_session6

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 93ee30f3e8b4 xsk: i40e: get rid of useless struct xdp_umem..
git tree: bpf-next
console output: https://syzkaller.appspot.com/x/log.txt?x=11f2115a400000
kernel config: https://syzkaller.appspot.com/x/.config?x=531a917630d2a492
dashboard link: https://syzkaller.appspot.com/bug?extid=acffccec848dc13fe459
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=116b3492400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+acffcc...@syzkaller.appspotmail.com

8021q: adding VLAN 0 to HW filter on device team0
8021q: adding VLAN 0 to HW filter on device team0
8021q: adding VLAN 0 to HW filter on device team0
8021q: adding VLAN 0 to HW filter on device team0
==================================================================
BUG: KASAN: slab-out-of-bounds in _decode_session6+0x1331/0x14e0
net/ipv6/xfrm6_policy.c:161
Read of size 1 at addr ffff8801d882eec7 by task syz-executor1/6667

CPU: 0 PID: 6667 Comm: syz-executor1 Not tainted 4.19.0-rc1+ #86
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+0x1c9/0x2b4 lib/dump_stack.c:113
print_address_description+0x6c/0x20b mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report.cold.7+0x242/0x30d mm/kasan/report.c:412
__asan_report_load1_noabort+0x14/0x20 mm/kasan/report.c:430
_decode_session6+0x1331/0x14e0 net/ipv6/xfrm6_policy.c:161
__xfrm_decode_session+0x71/0x140 net/xfrm/xfrm_policy.c:2299
xfrm_decode_session include/net/xfrm.h:1232 [inline]
vti6_tnl_xmit+0x3c3/0x1bc1 net/ipv6/ip6_vti.c:542
__netdev_start_xmit include/linux/netdevice.h:4313 [inline]
netdev_start_xmit include/linux/netdevice.h:4322 [inline]
xmit_one net/core/dev.c:3217 [inline]
dev_hard_start_xmit+0x272/0xc10 net/core/dev.c:3233
__dev_queue_xmit+0x2ab2/0x3870 net/core/dev.c:3803
dev_queue_xmit+0x17/0x20 net/core/dev.c:3836
__bpf_tx_skb net/core/filter.c:2012 [inline]
__bpf_redirect_common net/core/filter.c:2050 [inline]
__bpf_redirect+0x5b7/0xae0 net/core/filter.c:2057
____bpf_clone_redirect net/core/filter.c:2090 [inline]
bpf_clone_redirect+0x2f6/0x490 net/core/filter.c:2062
bpf_prog_c39d1ba309a769f7+0x749/0x1000

Allocated by task 6667:
save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
kasan_kmalloc+0xc4/0xe0 mm/kasan/kasan.c:553
__do_kmalloc_node mm/slab.c:3682 [inline]
__kmalloc_node_track_caller+0x47/0x70 mm/slab.c:3696
__kmalloc_reserve.isra.41+0x3a/0xe0 net/core/skbuff.c:137
pskb_expand_head+0x230/0x10e0 net/core/skbuff.c:1463
skb_ensure_writable+0x3dd/0x640 net/core/skbuff.c:5129
__bpf_try_make_writable net/core/filter.c:1633 [inline]
bpf_try_make_writable net/core/filter.c:1639 [inline]
bpf_try_make_head_writable net/core/filter.c:1647 [inline]
____bpf_clone_redirect net/core/filter.c:2084 [inline]
bpf_clone_redirect+0x14a/0x490 net/core/filter.c:2062
bpf_prog_c39d1ba309a769f7+0x749/0x1000

Freed by task 5493:
save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
__kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:521
kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
__cache_free mm/slab.c:3498 [inline]
kfree+0xd9/0x210 mm/slab.c:3813
skb_free_head+0x99/0xc0 net/core/skbuff.c:550
skb_release_data+0x6a4/0x880 net/core/skbuff.c:570
skb_release_all+0x4a/0x60 net/core/skbuff.c:627
__kfree_skb net/core/skbuff.c:641 [inline]
consume_skb+0x190/0x4e0 net/core/skbuff.c:701
netlink_dump+0xb14/0xd50 net/netlink/af_netlink.c:2269
netlink_recvmsg+0xf84/0x1490 net/netlink/af_netlink.c:1991
sock_recvmsg_nosec net/socket.c:794 [inline]
sock_recvmsg+0xd0/0x110 net/socket.c:801
___sys_recvmsg+0x2b6/0x680 net/socket.c:2276
__sys_recvmsg+0x11a/0x290 net/socket.c:2325
__do_sys_recvmsg net/socket.c:2335 [inline]
__se_sys_recvmsg net/socket.c:2332 [inline]
__x64_sys_recvmsg+0x78/0xb0 net/socket.c:2332
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8801d882ecc0
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 7 bytes to the right of
512-byte region [ffff8801d882ecc0, ffff8801d882eec0)
The buggy address belongs to the page:
page:ffffea0007620b80 count:1 mapcount:0 mapping:ffff8801dac00940 index:0x0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffffea00070fc048 ffffea00075f9c08 ffff8801dac00940
raw: 0000000000000000 ffff8801d882e040 0000000100000006 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801d882ed80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff8801d882ee00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> ffff8801d882ee80: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
^
ffff8801d882ef00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8801d882ef80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


---
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[Dmitry Vyukov]

On Sun, Sep 2, 2018 at 6:41 AM, syzbot
<syzbot+acffcc...@syzkaller.appspotmail.com> wrote:
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit: 93ee30f3e8b4 xsk: i40e: get rid of useless struct xdp_umem..
> git tree: bpf-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=11f2115a400000
> kernel config: https://syzkaller.appspot.com/x/.config?x=531a917630d2a492
> dashboard link: https://syzkaller.appspot.com/bug?extid=acffccec848dc13fe459
> compiler: gcc (GCC) 8.0.1 20180413 (experimental)
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=116b3492400000

Potentially this is bpf-related because the repro just runs a bpf
program. +bpf maintainers.

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> For more options, visit https://groups.google.com/d/optout.

[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit: b36fdc6853a3 Merge tag 'gpio-v4.19-2' of git://git.kernel...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=164938d1400000
kernel config: https://syzkaller.appspot.com/x/.config?x=4c7e83258d6e0156

dashboard link: https://syzkaller.appspot.com/bug?extid=acffccec848dc13fe459
compiler: gcc (GCC) 8.0.1 20180413 (experimental)

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=115f172e400000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16399be1400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+acffcc...@syzkaller.appspotmail.com

IPv6: ADDRCONF(NETDEV_UP): veth1: link is not ready
IPv6: ADDRCONF(NETDEV_CHANGE): veth1: link becomes ready
IPv6: ADDRCONF(NETDEV_CHANGE): veth0: link becomes ready

8021q: adding VLAN 0 to HW filter on device team0
==================================================================
BUG: KASAN: slab-out-of-bounds in _decode_session6+0x1331/0x14e0
net/ipv6/xfrm6_policy.c:161

Read of size 1 at addr ffff8801d4a67f07 by task syz-executor092/4673

CPU: 1 PID: 4673 Comm: syz-executor092 Not tainted 4.19.0-rc2+ #223

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+0x1c9/0x2b4 lib/dump_stack.c:113
print_address_description+0x6c/0x20b mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report.cold.7+0x242/0x30d mm/kasan/report.c:412
__asan_report_load1_noabort+0x14/0x20 mm/kasan/report.c:430
_decode_session6+0x1331/0x14e0 net/ipv6/xfrm6_policy.c:161
__xfrm_decode_session+0x71/0x140 net/xfrm/xfrm_policy.c:2299
xfrm_decode_session include/net/xfrm.h:1232 [inline]

vti6_tnl_xmit+0x3fc/0x1bb1 net/ipv6/ip6_vti.c:542
__netdev_start_xmit include/linux/netdevice.h:4287 [inline]
netdev_start_xmit include/linux/netdevice.h:4296 [inline]
xmit_one net/core/dev.c:3216 [inline]
dev_hard_start_xmit+0x272/0xc10 net/core/dev.c:3232
__dev_queue_xmit+0x2ab2/0x3870 net/core/dev.c:3802
dev_queue_xmit+0x17/0x20 net/core/dev.c:3835

__bpf_tx_skb net/core/filter.c:2012 [inline]
__bpf_redirect_common net/core/filter.c:2050 [inline]
__bpf_redirect+0x5b7/0xae0 net/core/filter.c:2057
____bpf_clone_redirect net/core/filter.c:2090 [inline]
bpf_clone_redirect+0x2f6/0x490 net/core/filter.c:2062

bpf_prog_c39d1ba309a769f7+0xe9e/0x1000

Allocated by task 4673:

save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
kasan_kmalloc+0xc4/0xe0 mm/kasan/kasan.c:553
__do_kmalloc_node mm/slab.c:3682 [inline]
__kmalloc_node_track_caller+0x47/0x70 mm/slab.c:3696
__kmalloc_reserve.isra.41+0x3a/0xe0 net/core/skbuff.c:137
pskb_expand_head+0x230/0x10e0 net/core/skbuff.c:1463
skb_ensure_writable+0x3dd/0x640 net/core/skbuff.c:5129
__bpf_try_make_writable net/core/filter.c:1633 [inline]
bpf_try_make_writable net/core/filter.c:1639 [inline]
bpf_try_make_head_writable net/core/filter.c:1647 [inline]
____bpf_clone_redirect net/core/filter.c:2084 [inline]
bpf_clone_redirect+0x14a/0x490 net/core/filter.c:2062

bpf_prog_c39d1ba309a769f7+0xe9e/0x1000

Freed by task 3286:

save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
__kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:521
kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
__cache_free mm/slab.c:3498 [inline]
kfree+0xd9/0x210 mm/slab.c:3813

load_elf_binary+0x2569/0x5610 fs/binfmt_elf.c:1118
search_binary_handler+0x17d/0x570 fs/exec.c:1653
exec_binprm fs/exec.c:1695 [inline]
__do_execve_file.isra.35+0x15ff/0x2460 fs/exec.c:1819
do_execveat_common fs/exec.c:1866 [inline]
do_execve fs/exec.c:1883 [inline]
__do_sys_execve fs/exec.c:1964 [inline]
__se_sys_execve fs/exec.c:1959 [inline]
__x64_sys_execve+0x8f/0xc0 fs/exec.c:1959
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8801d4a67d00

which belongs to the cache kmalloc-512 of size 512
The buggy address is located 7 bytes to the right of

512-byte region [ffff8801d4a67d00, ffff8801d4a67f00)

The buggy address belongs to the page:

page:ffffea00075299c0 count:1 mapcount:0 mapping:ffff8801dac00940 index:0x0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffffea0007529988 ffffea0007529a48 ffff8801dac00940
raw: 0000000000000000 ffff8801d4a67080 0000000100000006 0000000000000000

page dumped because: kasan: bad access detected

Memory state around the buggy address:

ffff8801d4a67e00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff8801d4a67e80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> ffff8801d4a67f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff8801d4a67f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8801d4a68000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

[Eric Dumazet]

What about :

diff --git a/net/core/filter.c b/net/core/filter.c
index aecdeba052d3f0ff3d4f0a33ec36891f9738052c..a662f59786bd0677850c1c60a2c92faa6fb6c5bb 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2081,7 +2081,7 @@ BPF_CALL_3(bpf_clone_redirect, struct sk_buff *, skb, u32, ifindex, u64, flags)
* here, we need to free the just generated clone to unclone once
* again.
*/
- ret = bpf_try_make_head_writable(skb);
+ ret = bpf_try_make_head_writable(clone);
if (unlikely(ret)) {
kfree_skb(clone);
return -ENOMEM;

[Alexei Starovoitov]

On Thu, Sep 06, 2018 at 12:00:26AM -0700, Eric Dumazet wrote:
>
>
> On 09/05/2018 08:17 PM, syzbot wrote:
> > syzbot has found a reproducer for the following crash on:
> >

> > HEAD commit:ááá b36fdc6853a3 Merge tag 'gpio-v4.19-2' of git://git.kernel...
> > git tree:áááááá upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=164938d1400000
> > kernel config:á https://syzkaller.appspot.com/x/.config?x=4c7e83258d6e0156
> > dashboard link: https://syzkaller.appspot.com/bug?extid=acffccec848dc13fe459
> > compiler:áááááá gcc (GCC) 8.0.1 20180413 (experimental)
> > syz repro:ááááá https://syzkaller.appspot.com/x/repro.syz?x=115f172e400000
> > C reproducer:áá https://syzkaller.appspot.com/x/repro.c?x=16399be1400000

> >
> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > Reported-by: syzbot+acffcc...@syzkaller.appspotmail.com
> >
> > IPv6: ADDRCONF(NETDEV_UP): veth1: link is not ready
> > IPv6: ADDRCONF(NETDEV_CHANGE): veth1: link becomes ready
> > IPv6: ADDRCONF(NETDEV_CHANGE): veth0: link becomes ready
> > 8021q: adding VLAN 0 to HW filter on device team0
> > ==================================================================
> > BUG: KASAN: slab-out-of-bounds in _decode_session6+0x1331/0x14e0 net/ipv6/xfrm6_policy.c:161
> > Read of size 1 at addr ffff8801d4a67f07 by task syz-executor092/4673
> >
> > CPU: 1 PID: 4673 Comm: syz-executor092 Not tainted 4.19.0-rc2+ #223
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> > Call Trace:

> > á__dump_stack lib/dump_stack.c:77 [inline]
> > ádump_stack+0x1c9/0x2b4 lib/dump_stack.c:113
> > áprint_address_description+0x6c/0x20b mm/kasan/report.c:256
> > ákasan_report_error mm/kasan/report.c:354 [inline]
> > ákasan_report.cold.7+0x242/0x30d mm/kasan/report.c:412
> > á__asan_report_load1_noabort+0x14/0x20 mm/kasan/report.c:430
> > á_decode_session6+0x1331/0x14e0 net/ipv6/xfrm6_policy.c:161
> > á__xfrm_decode_session+0x71/0x140 net/xfrm/xfrm_policy.c:2299
> > áxfrm_decode_session include/net/xfrm.h:1232 [inline]
> > ávti6_tnl_xmit+0x3fc/0x1bb1 net/ipv6/ip6_vti.c:542
> > á__netdev_start_xmit include/linux/netdevice.h:4287 [inline]
> > ánetdev_start_xmit include/linux/netdevice.h:4296 [inline]
> > áxmit_one net/core/dev.c:3216 [inline]
> > ádev_hard_start_xmit+0x272/0xc10 net/core/dev.c:3232
> > á__dev_queue_xmit+0x2ab2/0x3870 net/core/dev.c:3802
> > ádev_queue_xmit+0x17/0x20 net/core/dev.c:3835
> > á__bpf_tx_skb net/core/filter.c:2012 [inline]
> > á__bpf_redirect_common net/core/filter.c:2050 [inline]
> > á__bpf_redirect+0x5b7/0xae0 net/core/filter.c:2057
> > á____bpf_clone_redirect net/core/filter.c:2090 [inline]
> > ábpf_clone_redirect+0x2f6/0x490 net/core/filter.c:2062
> > ábpf_prog_c39d1ba309a769f7+0xe9e/0x1000
> >
> > Allocated by task 4673:
> > ásave_stack+0x43/0xd0 mm/kasan/kasan.c:448
> > áset_track mm/kasan/kasan.c:460 [inline]
> > ákasan_kmalloc+0xc4/0xe0 mm/kasan/kasan.c:553
> > á__do_kmalloc_node mm/slab.c:3682 [inline]
> > á__kmalloc_node_track_caller+0x47/0x70 mm/slab.c:3696
> > á__kmalloc_reserve.isra.41+0x3a/0xe0 net/core/skbuff.c:137
> > ápskb_expand_head+0x230/0x10e0 net/core/skbuff.c:1463
> > áskb_ensure_writable+0x3dd/0x640 net/core/skbuff.c:5129
> > á__bpf_try_make_writable net/core/filter.c:1633 [inline]
> > ábpf_try_make_writable net/core/filter.c:1639 [inline]
> > ábpf_try_make_head_writable net/core/filter.c:1647 [inline]
> > á____bpf_clone_redirect net/core/filter.c:2084 [inline]
> > ábpf_clone_redirect+0x14a/0x490 net/core/filter.c:2062
> > ábpf_prog_c39d1ba309a769f7+0xe9e/0x1000
> >
> > Freed by task 3286:
> > ásave_stack+0x43/0xd0 mm/kasan/kasan.c:448
> > áset_track mm/kasan/kasan.c:460 [inline]
> > á__kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:521
> > ákasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
> > á__cache_free mm/slab.c:3498 [inline]
> > ákfree+0xd9/0x210 mm/slab.c:3813
> > áload_elf_binary+0x2569/0x5610 fs/binfmt_elf.c:1118
> > ásearch_binary_handler+0x17d/0x570 fs/exec.c:1653
> > áexec_binprm fs/exec.c:1695 [inline]
> > á__do_execve_file.isra.35+0x15ff/0x2460 fs/exec.c:1819
> > ádo_execveat_common fs/exec.c:1866 [inline]
> > ádo_execve fs/exec.c:1883 [inline]
> > á__do_sys_execve fs/exec.c:1964 [inline]
> > á__se_sys_execve fs/exec.c:1959 [inline]
> > á__x64_sys_execve+0x8f/0xc0 fs/exec.c:1959
> > ádo_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
> > áentry_SYSCALL_64_after_hwframe+0x49/0xbe

> >
> > The buggy address belongs to the object at ffff8801d4a67d00

> > áwhich belongs to the cache kmalloc-512 of size 512

> > The buggy address is located 7 bytes to the right of

> > á512-byte region [ffff8801d4a67d00, ffff8801d4a67f00)

> > The buggy address belongs to the page:
> > page:ffffea00075299c0 count:1 mapcount:0 mapping:ffff8801dac00940 index:0x0
> > flags: 0x2fffc0000000100(slab)
> > raw: 02fffc0000000100 ffffea0007529988 ffffea0007529a48 ffff8801dac00940
> > raw: 0000000000000000 ffff8801d4a67080 0000000100000006 0000000000000000
> > page dumped because: kasan: bad access detected
> >
> > Memory state around the buggy address:

> > áffff8801d4a67e00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> > áffff8801d4a67e80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

> >> ffff8801d4a67f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc

> > áááááááááááááááááá ^
> > áffff8801d4a67f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> > áffff8801d4a68000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

> > ==================================================================
> >
>
>
> What about :
>
> diff --git a/net/core/filter.c b/net/core/filter.c
> index aecdeba052d3f0ff3d4f0a33ec36891f9738052c..a662f59786bd0677850c1c60a2c92faa6fb6c5bb 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -2081,7 +2081,7 @@ BPF_CALL_3(bpf_clone_redirect, struct sk_buff *, skb, u32, ifindex, u64, flags)
> * here, we need to free the just generated clone to unclone once
> * again.
> */
> - ret = bpf_try_make_head_writable(skb);
> + ret = bpf_try_make_head_writable(clone);

This part is fine. I think the bug is in _decode_session6,
but I have a hard time reproducing the issue, so will appreciate
if somebody can test the following patch:

From 291f80f212461670d1e0140d06eee3071cf3e1ee Mon Sep 17 00:00:00 2001
From: Alexei Starovoitov <a...@kernel.org>
Date: Thu, 6 Sep 2018 10:23:29 -0700
Subject: [PATCH] net/xfrm: fix out-of-bounds packet access

BUG: KASAN: slab-out-of-bounds in _decode_session6+0x1331/0x14e0
net/ipv6/xfrm6_policy.c:161

Read of size 1 at addr ffff8801d882eec7 by task syz-executor1/6667

Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x1c9/0x2b4 lib/dump_stack.c:113
print_address_description+0x6c/0x20b mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report.cold.7+0x242/0x30d mm/kasan/report.c:412
__asan_report_load1_noabort+0x14/0x20 mm/kasan/report.c:430
_decode_session6+0x1331/0x14e0 net/ipv6/xfrm6_policy.c:161
__xfrm_decode_session+0x71/0x140 net/xfrm/xfrm_policy.c:2299
xfrm_decode_session include/net/xfrm.h:1232 [inline]

vti6_tnl_xmit+0x3c3/0x1bc1 net/ipv6/ip6_vti.c:542
__netdev_start_xmit include/linux/netdevice.h:4313 [inline]
netdev_start_xmit include/linux/netdevice.h:4322 [inline]
xmit_one net/core/dev.c:3217 [inline]
dev_hard_start_xmit+0x272/0xc10 net/core/dev.c:3233
__dev_queue_xmit+0x2ab2/0x3870 net/core/dev.c:3803
dev_queue_xmit+0x17/0x20 net/core/dev.c:3836

Reported-by: syzbot+acffcc...@syzkaller.appspotmail.com
Signed-off-by: Alexei Starovoitov <a...@kernel.org>
---
net/ipv6/xfrm6_policy.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/xfrm6_policy.c b/net/ipv6/xfrm6_policy.c
index ef3defaf43b9..d35bcf92969c 100644
--- a/net/ipv6/xfrm6_policy.c
+++ b/net/ipv6/xfrm6_policy.c
@@ -146,8 +146,8 @@ _decode_session6(struct sk_buff *skb, struct flowi *fl, int reverse)
fl6->daddr = reverse ? hdr->saddr : hdr->daddr;
fl6->saddr = reverse ? hdr->daddr : hdr->saddr;

- while (nh + offset + 1 < skb->data ||
- pskb_may_pull(skb, nh + offset + 1 - skb->data)) {
+ while (nh + offset + sizeof(*exthdr) < skb->data ||
+ pskb_may_pull(skb, nh + offset + sizeof(*exthdr) - skb->data)) {
nh = skb_network_header(skb);
exthdr = (struct ipv6_opt_hdr *)(nh + offset);

--
2.17.1

[Dmitry Vyukov]

Eric, you arrived to roughly the same conclusion, right?

> but I have a hard time reproducing the issue, so will appreciate
> if somebody can test the following patch:

syzbot can:
https://github.com/google/syzkaller/blob/master/docs/syzbot.md#testing-patches

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