[syzbot] general protection fault in smc_tx_sendmsg

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 0c337952 Merge tag 'wireless-drivers-next-2021-06-16' of g..
git tree: net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1621de10300000
kernel config: https://syzkaller.appspot.com/x/.config?x=a6380da8984033f1
dashboard link: https://syzkaller.appspot.com/bug?extid=5dda108b672b54141857
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=121d2d20300000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=100bd768300000

The issue was bisected to:

commit f9006acc8dfe59e25aa75729728ac57a8d84fc32
Author: Florian Westphal <f...@strlen.de>
Date: Wed Apr 21 07:51:08 2021 +0000

netfilter: arp_tables: pass table pointer via nf_hook_ops

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=12600fffd00000
final oops: https://syzkaller.appspot.com/x/report.txt?x=11600fffd00000
console output: https://syzkaller.appspot.com/x/log.txt?x=16600fffd00000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5dda10...@syzkaller.appspotmail.com
Fixes: f9006acc8dfe ("netfilter: arp_tables: pass table pointer via nf_hook_ops")

general protection fault, probably for non-canonical address 0xdffffc0000000004: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000020-0x0000000000000027]
CPU: 1 PID: 8455 Comm: syz-executor893 Not tainted 5.13.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:smc_tx_sendmsg+0x204/0x1ba0 net/smc/smc_tx.c:157
Code: 48 c1 ea 03 80 3c 02 00 0f 85 8b 17 00 00 49 8b 9d 08 05 00 00 48 b8 00 00 00 00 00 fc ff df 48 8d 7b 20 48 89 fa 48 c1 ea 03 <0f> b6 04 02 84 c0 74 08 3c 03 0f 8e 8f 17 00 00 48 63 5b 20 4c 8b
RSP: 0018:ffffc9000164f800 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000004 RSI: ffffffff889cd6ae RDI: 0000000000000020
RBP: ffff88801cf58000 R08: 0000000000000000 R09: 0000000000000000
R10: ffffffff889cd6a1 R11: 0000000000000000 R12: 0000000000000000
R13: ffff88801cf58000 R14: ffffc9000164fd90 R15: ffff88801cf58060
FS: 0000000000ebf300(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffd43ca1328 CR3: 000000002acf2000 CR4: 00000000001506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
smc_sendmsg+0x274/0x5b0 net/smc/af_smc.c:2037
sock_sendmsg_nosec net/socket.c:654 [inline]
sock_sendmsg+0xcf/0x120 net/socket.c:674
____sys_sendmsg+0x331/0x810 net/socket.c:2350
___sys_sendmsg+0xf3/0x170 net/socket.c:2404
__sys_sendmmsg+0x195/0x470 net/socket.c:2490
__do_sys_sendmmsg net/socket.c:2519 [inline]
__se_sys_sendmmsg net/socket.c:2516 [inline]
__x64_sys_sendmmsg+0x99/0x100 net/socket.c:2516
do_syscall_64+0x3a/0xb0 arch/x86/entry/common.c:47
entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x43ee89
Code: 28 c3 e8 2a 14 00 00 66 2e 0f 1f 84 00 00 00 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffc82b20a58 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 0000000000400488 RCX: 000000000043ee89
RDX: 0000000000000001 RSI: 0000000020003d80 RDI: 0000000000000003
RBP: 0000000000402e70 R08: 0000000000000000 R09: 0000000000400488
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000402f00
R13: 0000000000000000 R14: 00000000004ac018 R15: 0000000000400488
Modules linked in:
---[ end trace 459b28282ae53115 ]---
RIP: 0010:smc_tx_sendmsg+0x204/0x1ba0 net/smc/smc_tx.c:157
Code: 48 c1 ea 03 80 3c 02 00 0f 85 8b 17 00 00 49 8b 9d 08 05 00 00 48 b8 00 00 00 00 00 fc ff df 48 8d 7b 20 48 89 fa 48 c1 ea 03 <0f> b6 04 02 84 c0 74 08 3c 03 0f 8e 8f 17 00 00 48 63 5b 20 4c 8b
RSP: 0018:ffffc9000164f800 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000004 RSI: ffffffff889cd6ae RDI: 0000000000000020
RBP: ffff88801cf58000 R08: 0000000000000000 R09: 0000000000000000
R10: ffffffff889cd6a1 R11: 0000000000000000 R12: 0000000000000000
R13: ffff88801cf58000 R14: ffffc9000164fd90 R15: ffff88801cf58060
FS: 0000000000ebf300(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055b7501be298 CR3: 000000002acf2000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
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For information about bisection process see: https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this issue, for details see:
https://goo.gl/tpsmEJ#testing-patches

[Pavel Skripkin]

On Sun, 20 Jun 2021 16:22:16 -0700
syzbot <syzbot+5dda10...@syzkaller.appspotmail.com> wrote:

> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 0c337952 Merge tag 'wireless-drivers-next-2021-06-16'
> of g.. git tree: net-next
> console output:
> https://syzkaller.appspot.com/x/log.txt?x=1621de10300000 kernel
> config: https://syzkaller.appspot.com/x/.config?x=a6380da8984033f1
> dashboard link:
> https://syzkaller.appspot.com/bug?extid=5dda108b672b54141857 syz
> repro:
> https://syzkaller.appspot.com/x/repro.syz?x=121d2d20300000 C
> reproducer: https://syzkaller.appspot.com/x/repro.c?x=100bd768300000
>
> The issue was bisected to:
>
> commit f9006acc8dfe59e25aa75729728ac57a8d84fc32
> Author: Florian Westphal <f...@strlen.de>
> Date: Wed Apr 21 07:51:08 2021 +0000
>
> netfilter: arp_tables: pass table pointer via nf_hook_ops
>

I think, bisection is wrong this time :)

It should be e0e4b8fa533858532f1b9ea9c6a4660d09beb37a ("net/smc: Add SMC
statistics support")


Some debug results:

syzkaller repro just opens the socket and calls sendmsg. Ftrace log:


0) | smc_create() {
0) | smc_sock_alloc() {
0) + 88.493 us | smc_hash_sk();
0) ! 131.487 us | }
0) ! 189.912 us | }
0) | smc_sendmsg() {
0) 2.808 us | smc_tx_sendmsg();
0) ! 148.484 us | }


That means, that smc_buf_create() wasn't called at all, so we need to
check sndbuf_desc before dereferencing

Something like this should work

diff --git a/net/smc/smc_tx.c b/net/smc/smc_tx.c
index 075c4f4b4..e24071b12 100644
--- a/net/smc/smc_tx.c
+++ b/net/smc/smc_tx.c
@@ -154,7 +154,7 @@ int smc_tx_sendmsg(struct smc_sock *smc, struct msghdr *msg, size_t len)
goto out_err;
}

- if (len > conn->sndbuf_desc->len)
+ if (conn->sndbuf_desc && len > conn->sndbuf_desc->len)
SMC_STAT_RMB_TX_SIZE_SMALL(smc, !conn->lnk);

if (len > conn->peer_rmbe_size)


Thoughts?


+CC Guvenc Gulce


With regards,
Pavel Skripkin

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
general protection fault in smc_tx_sendmsg

general protection fault, probably for non-canonical address 0xdffffc0000000004: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000020-0x0000000000000027]

CPU: 0 PID: 10201 Comm: syz-executor.2 Not tainted 5.13.0-rc6-syzkaller #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:smc_tx_sendmsg+0x204/0x1ba0 net/smc/smc_tx.c:157
Code: 48 c1 ea 03 80 3c 02 00 0f 85 8b 17 00 00 49 8b 9d 08 05 00 00 48 b8 00 00 00 00 00 fc ff df 48 8d 7b 20 48 89 fa 48 c1 ea 03 <0f> b6 04 02 84 c0 74 08 3c 03 0f 8e 8f 17 00 00 48 63 5b 20 4c 8b

RSP: 0018:ffffc9000b43f800 EFLAGS: 00010202

RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000

RDX: 0000000000000004 RSI: ffffffff889daebe RDI: 0000000000000020
RBP: ffff88802f8f8000 R08: 0000000000000000 R09: 0000000000000000
R10: ffffffff889daeb1 R11: 0000000000000000 R12: 0000000000000000
R13: ffff88802f8f8000 R14: ffffc9000b43fd90 R15: ffff88802f8f8060
FS: 00007f25f7bdd700(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 0000000000529330 CR3: 00000000135d1000 CR4: 00000000001506f0

DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

Call Trace:
smc_sendmsg+0x274/0x5b0 net/smc/af_smc.c:2037
sock_sendmsg_nosec net/socket.c:654 [inline]
sock_sendmsg+0xcf/0x120 net/socket.c:674

____sys_sendmsg+0x331/0x810 net/socket.c:2337
___sys_sendmsg+0xf3/0x170 net/socket.c:2391
__sys_sendmmsg+0x195/0x470 net/socket.c:2477
__do_sys_sendmmsg net/socket.c:2506 [inline]
__se_sys_sendmmsg net/socket.c:2503 [inline]
__x64_sys_sendmmsg+0x99/0x100 net/socket.c:2503
do_syscall_64+0x3a/0xb0 arch/x86/entry/common.c:47
entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x4665d9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f25f7bdd188 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 000000000056bf80 RCX: 00000000004665d9

RDX: 0000000000000001 RSI: 0000000020003d80 RDI: 0000000000000003

RBP: 00000000004bfcb9 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000056bf80
R13: 00007ffd9bc0bfef R14: 00007f25f7bdd300 R15: 0000000000022000
Modules linked in:
---[ end trace 156371c760a91fce ]---

RIP: 0010:smc_tx_sendmsg+0x204/0x1ba0 net/smc/smc_tx.c:157
Code: 48 c1 ea 03 80 3c 02 00 0f 85 8b 17 00 00 49 8b 9d 08 05 00 00 48 b8 00 00 00 00 00 fc ff df 48 8d 7b 20 48 89 fa 48 c1 ea 03 <0f> b6 04 02 84 c0 74 08 3c 03 0f 8e 8f 17 00 00 48 63 5b 20 4c 8b

Tested on:

commit: adc2e56e Merge git://git.kernel.org/pub/scm/linux/kernel/g..
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=14ed9734300000
kernel config: https://syzkaller.appspot.com/x/.config?x=378e6e06e1908cc3
dashboard link: https://syzkaller.appspot.com/bug?extid=5dda108b672b54141857
compiler:

[Guvenc Gulce]

Thanks for analyzing the cause. Your approach would work but I would prefer that we
check the state of the socket before doing the statistics relevant if check. This will ensure
that smc_buf_create() was already called.
I am testing the fix at the moment which would look like the following:

diff --git a/net/smc/smc_tx.c b/net/smc/smc_tx.c
index 075c4f4b41cf..289025cd545a 100644
--- a/net/smc/smc_tx.c
+++ b/net/smc/smc_tx.c
@@ -154,6 +154,9 @@ int smc_tx_sendmsg(struct smc_sock *smc, struct msghdr *msg, size_t len)
                goto out_err;
        }

+       if (sk->sk_state == SMC_INIT)
+               return -ENOTCONN;
+

        if (len > conn->sndbuf_desc->len)

                SMC_STAT_RMB_TX_SIZE_SMALL(smc, !conn->lnk);

[Pavel Skripkin]

This sounds better. I knew, that my approach will just "silence" the
bug, that's why I CCed you for better approach :)

> diff --git a/net/smc/smc_tx.c b/net/smc/smc_tx.c
> index 075c4f4b41cf..289025cd545a 100644
> --- a/net/smc/smc_tx.c
> +++ b/net/smc/smc_tx.c
> @@ -154,6 +154,9 @@ int smc_tx_sendmsg(struct smc_sock *smc, struct
> msghdr *msg, size_t len) goto out_err;
>         }
>
> +       if (sk->sk_state == SMC_INIT)
> +               return -ENOTCONN;
> +
>         if (len > conn->sndbuf_desc->len)
>                 SMC_STAT_RMB_TX_SIZE_SMALL(smc, !conn->lnk);
>
>

With regards,
Pavel Skripkin