KMSAN: uninit-value in ebt_stp_mt_check (2)

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syzbot

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Jun 7, 2018, 1:29:03 PM6/7/18
to bri...@lists.linux-foundation.org, core...@netfilter.org, da...@davemloft.net, f...@strlen.de, kad...@blackhole.kfki.hu, linux-...@vger.kernel.org, net...@vger.kernel.org, netfilt...@vger.kernel.org, pa...@netfilter.org, ste...@networkplumber.org, syzkall...@googlegroups.com
Hello,

syzbot found the following crash on:

HEAD commit: c6a6aed994b6 kmsan: remove dead code to trigger syzbot build
git tree: https://github.com/google/kmsan.git/master
console output: https://syzkaller.appspot.com/x/log.txt?x=17bde74f800000
kernel config: https://syzkaller.appspot.com/x/.config?x=848e40757852af3e
dashboard link: https://syzkaller.appspot.com/bug?extid=da4494182233c23a5fcf
compiler: clang version 7.0.0 (trunk 334104)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+da4494...@syzkaller.appspotmail.com

==================================================================
BUG: KMSAN: uninit-value in ebt_stp_mt_check+0x24b/0x450
net/bridge/netfilter/ebt_stp.c:162
CPU: 0 PID: 12006 Comm: syz-executor7 Not tainted 4.17.0+ #3
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+0x185/0x1d0 lib/dump_stack.c:113
kmsan_report+0x149/0x260 mm/kmsan/kmsan.c:1084
__msan_warning_32+0x6e/0xc0 mm/kmsan/kmsan_instr.c:620
ebt_stp_mt_check+0x24b/0x450 net/bridge/netfilter/ebt_stp.c:162
xt_check_match+0x1438/0x1650 net/netfilter/x_tables.c:506
ebt_check_match net/bridge/netfilter/ebtables.c:372 [inline]
ebt_check_entry net/bridge/netfilter/ebtables.c:702 [inline]
translate_table+0x4e88/0x6120 net/bridge/netfilter/ebtables.c:943
do_replace_finish+0x1258/0x2ea0 net/bridge/netfilter/ebtables.c:999
do_replace+0x719/0x780 net/bridge/netfilter/ebtables.c:1138
do_ebt_set_ctl+0x2ab/0x3c0 net/bridge/netfilter/ebtables.c:1517
nf_sockopt net/netfilter/nf_sockopt.c:106 [inline]
nf_setsockopt+0x47c/0x4e0 net/netfilter/nf_sockopt.c:115
ip_setsockopt+0x24b/0x2b0 net/ipv4/ip_sockglue.c:1251
udp_setsockopt+0x108/0x1b0 net/ipv4/udp.c:2416
sock_common_setsockopt+0x13b/0x170 net/core/sock.c:3039
__sys_setsockopt+0x496/0x540 net/socket.c:1903
__do_sys_setsockopt net/socket.c:1914 [inline]
__se_sys_setsockopt net/socket.c:1911 [inline]
__x64_sys_setsockopt+0x15c/0x1c0 net/socket.c:1911
do_syscall_64+0x15b/0x230 arch/x86/entry/common.c:287
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x4559f9
RSP: 002b:00007f45b9246c68 EFLAGS: 00000246 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 00007f45b92476d4 RCX: 00000000004559f9
RDX: 0000000000000080 RSI: 0000000000000000 RDI: 0000000000000014
RBP: 000000000072bea0 R08: 0000000000000300 R09: 0000000000000000
R10: 0000000020000480 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000004c0d6d R14: 00000000004d07c8 R15: 0000000000000000

Local variable description: ----mtpar.i@translate_table
Variable was created at:
translate_table+0xbb/0x6120 net/bridge/netfilter/ebtables.c:831
do_replace_finish+0x1258/0x2ea0 net/bridge/netfilter/ebtables.c:999
==================================================================


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

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syzbot.

Dmitry Vyukov

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Jun 7, 2018, 1:34:32 PM6/7/18
to syzbot, bri...@lists.linux-foundation.org, core...@netfilter.org, David Miller, Florian Westphal, Jozsef Kadlecsik, LKML, netdev, netfilt...@vger.kernel.org, Pablo Neira Ayuso, stephen hemminger, syzkaller-bugs
On Thu, Jun 7, 2018 at 7:29 PM, syzbot
<syzbot+da4494...@syzkaller.appspotmail.com> wrote:
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit: c6a6aed994b6 kmsan: remove dead code to trigger syzbot build
> git tree: https://github.com/google/kmsan.git/master
> console output: https://syzkaller.appspot.com/x/log.txt?x=17bde74f800000
> kernel config: https://syzkaller.appspot.com/x/.config?x=848e40757852af3e
> dashboard link: https://syzkaller.appspot.com/bug?extid=da4494182233c23a5fcf
> compiler: clang version 7.0.0 (trunk 334104)
>
> Unfortunately, I don't have any reproducer for this crash yet.
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+da4494...@syzkaller.appspotmail.com

Hi Stephen,

This strikes again.

The first part of the check is par->nft_compat. I don't see where
ebt_check_entry initializes it. Should it? Or matches should not look at it?
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> For more options, visit https://groups.google.com/d/optout.

Florian Westphal

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Jun 7, 2018, 3:36:29 PM6/7/18
to netfilt...@vger.kernel.org, syzkall...@googlegroups.com, Florian Westphal
syzbot reports following splat:

BUG: KMSAN: uninit-value in ebt_stp_mt_check+0x24b/0x450
net/bridge/netfilter/ebt_stp.c:162
ebt_stp_mt_check+0x24b/0x450 net/bridge/netfilter/ebt_stp.c:162
xt_check_match+0x1438/0x1650 net/netfilter/x_tables.c:506
ebt_check_match net/bridge/netfilter/ebtables.c:372 [inline]
ebt_check_entry net/bridge/netfilter/ebtables.c:702 [inline]

The uninitialised access is
xt_mtchk_param->nft_compat

... which should be set to 0.
Fix it by zeroing the struct beforehand, same for tgchk.

ip(6)tables targetinfo uses c99-style initialiser, so no change
needed there.

Reported-by: syzbot+da4494...@syzkaller.appspotmail.com
Fixes: 55917a21d0cc0 ("netfilter: x_tables: add context to know if extension runs from nft_compat")
Signed-off-by: Florian Westphal <f...@strlen.de>
---
net/bridge/netfilter/ebtables.c | 2 ++
net/ipv4/netfilter/ip_tables.c | 1 +
net/ipv6/netfilter/ip6_tables.c | 1 +
3 files changed, 4 insertions(+)

diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c
index c2138e7e8263..93600aa606a8 100644
--- a/net/bridge/netfilter/ebtables.c
+++ b/net/bridge/netfilter/ebtables.c
@@ -709,6 +709,8 @@ ebt_check_entry(struct ebt_entry *e, struct net *net,
}
i = 0;

+ memset(&mtpar, 0, sizeof(mtpar));
+ memset(&tgpar, 0, sizeof(tgpar));
mtpar.net = tgpar.net = net;
mtpar.table = tgpar.table = name;
mtpar.entryinfo = tgpar.entryinfo = e;
diff --git a/net/ipv4/netfilter/ip_tables.c b/net/ipv4/netfilter/ip_tables.c
index 38ab97b0a2ec..ca0dad90803a 100644
--- a/net/ipv4/netfilter/ip_tables.c
+++ b/net/ipv4/netfilter/ip_tables.c
@@ -531,6 +531,7 @@ find_check_entry(struct ipt_entry *e, struct net *net, const char *name,
return -ENOMEM;

j = 0;
+ memset(&mtpar, 0, sizeof(mtpar));
mtpar.net = net;
mtpar.table = name;
mtpar.entryinfo = &e->ip;
diff --git a/net/ipv6/netfilter/ip6_tables.c b/net/ipv6/netfilter/ip6_tables.c
index 0758b5bcfb29..7eab959734bc 100644
--- a/net/ipv6/netfilter/ip6_tables.c
+++ b/net/ipv6/netfilter/ip6_tables.c
@@ -550,6 +550,7 @@ find_check_entry(struct ip6t_entry *e, struct net *net, const char *name,
return -ENOMEM;

j = 0;
+ memset(&mtpar, 0, sizeof(mtpar));
mtpar.net = net;
mtpar.table = name;
mtpar.entryinfo = &e->ipv6;
--
2.16.4

syzbot

unread,
Jun 7, 2018, 5:40:02 PM6/7/18
to bri...@lists.linux-foundation.org, core...@netfilter.org, da...@davemloft.net, dvy...@google.com, f...@strlen.de, kad...@blackhole.kfki.hu, linux-...@vger.kernel.org, net...@vger.kernel.org, netfilt...@vger.kernel.org, pa...@netfilter.org, ste...@networkplumber.org, syzkall...@googlegroups.com
syzbot has found a reproducer for the following crash on:

HEAD commit: c6a6aed994b6 kmsan: remove dead code to trigger syzbot build
git tree: https://github.com/google/kmsan.git/master
console output: https://syzkaller.appspot.com/x/log.txt?x=122606bf800000
kernel config: https://syzkaller.appspot.com/x/.config?x=848e40757852af3e
dashboard link: https://syzkaller.appspot.com/bug?extid=da4494182233c23a5fcf
compiler: clang version 7.0.0 (trunk 334104)
syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=121f481f800000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=121fbbd7800000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+da4494...@syzkaller.appspotmail.com

random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
==================================================================
BUG: KMSAN: uninit-value in ebt_stp_mt_check+0x24b/0x450
net/bridge/netfilter/ebt_stp.c:162
CPU: 1 PID: 4523 Comm: syz-executor710 Not tainted 4.17.0+ #3
RIP: 0033:0x43fd89
RSP: 002b:00007ffc9d7edb28 EFLAGS: 00000213 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 000000000043fd89
RDX: 0000000000000080 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00000000006ca018 R08: 0000000000000300 R09: 00000000004002c8
R10: 0000000020000480 R11: 0000000000000213 R12: 00000000004016b0
R13: 0000000000401740 R14: 0000000000000000 R15: 0000000000000000

Pablo Neira Ayuso

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Jun 8, 2018, 6:41:41 AM6/8/18
to Florian Westphal, netfilt...@vger.kernel.org, syzkall...@googlegroups.com
On Thu, Jun 07, 2018 at 09:34:43PM +0200, Florian Westphal wrote:
> syzbot reports following splat:
>
> BUG: KMSAN: uninit-value in ebt_stp_mt_check+0x24b/0x450
> net/bridge/netfilter/ebt_stp.c:162
> ebt_stp_mt_check+0x24b/0x450 net/bridge/netfilter/ebt_stp.c:162
> xt_check_match+0x1438/0x1650 net/netfilter/x_tables.c:506
> ebt_check_match net/bridge/netfilter/ebtables.c:372 [inline]
> ebt_check_entry net/bridge/netfilter/ebtables.c:702 [inline]
>
> The uninitialised access is
> xt_mtchk_param->nft_compat
>
> ... which should be set to 0.
> Fix it by zeroing the struct beforehand, same for tgchk.
>
> ip(6)tables targetinfo uses c99-style initialiser, so no change
> needed there.

Applied, thanks Florian.
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