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Message-ID: <1342678175.2626.3849.camel@edumazet-glaptop>
Date: Thu, 19 Jul 2012 08:09:35 +0200
From: Eric Dumazet <eric.dumazet@...il.com>
To: Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>
Cc: Maxim Krasnyansky <maxk@...lcomm.com>, vtun@...ice.satix.net,
netdev@...r.kernel.org, davem@...emloft.net
Subject: Re: [PATCH] Crash in tun
On Thu, 2012-07-19 at 03:12 +0200, Mikulas Patocka wrote:
> Hi
>
> I want to report a crash when using the tun driver. The crash can be
> reproduced by starting and stopping miredo in the loop:
>
> while ! dmesg | grep -q BUG; do
> /etc/init.d/miredo start;/etc/init.d/miredo stop
> done
>
> The crash happens in iput_final because inode->i_sb->s_op is NULL.
>
> The crash happens in 3.4, 3.4.5, 3.5-rc7. The crash does not happen in
> 3.3. When I attempted to bisect, unrelated changes in completely different
> driver regarding memory allocation triggered the crash --- so it is
> likely buggy even in 3.3 and before, it just didn't show up.
>
>
> What is obviously wrong:
> in the tun driver "struct socket" is embedded in "struct tun_struct".
>
> The backtrace goes through:
> netdev_run_todo -> tun_free_netdev -> sk_release_kernel -> sock_release.
>
> sock_release calls iput(SOCK_INODE(sock)). SOCK_INODE assumes that struct
> socket is embedded in "struct socket_alloc" (which is not true, it is
> embedded in "struct tun_struct"), gets a pointer to non-existing inode ---
> and there goes the crash.
>
>
> The crash can be fixed by writing any non-NULL value to tun->socket.file
> to prevent sock_release from calling iput(SOCK_INODE(sock)). Or maybe you
> come up with a better fix.
>
>
> Note another bug - when you are repeatedly starting and stopping miredo,
> even if it doesn't crash, the value "sockets: used" in
> /proc/*/net/sockstat keeps on decreasing. That's because sock_release
> decrements sockets_in_use, but there was no sock_alloc to increment it.
>
>
> Mikulas
>
> ---
>
> Signed-off-by: Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>
>
> ---
> drivers/net/tun.c | 2 ++
> net/socket.c | 4 +++-
> 2 files changed, 5 insertions(+), 1 deletion(-)
>
> Index: linux-3.4.5-fast/drivers/net/tun.c
> ===================================================================
> --- linux-3.4.5-fast.orig/drivers/net/tun.c 2012-07-19 02:42:56.000000000 +0200
> +++ linux-3.4.5-fast/drivers/net/tun.c 2012-07-19 02:50:13.000000000 +0200
> @@ -358,6 +358,8 @@ static void tun_free_netdev(struct net_d
> {
> struct tun_struct *tun = netdev_priv(dev);
>
> + /* Prevent the code in sock_release from calling iput. */
> + tun->socket.file = (void *)1;
> sk_release_kernel(tun->socket.sk);
> }
>
> Index: linux-3.4.5-fast/net/socket.c
> ===================================================================
> --- linux-3.4.5-fast.orig/net/socket.c 2012-07-19 03:00:30.000000000 +0200
> +++ linux-3.4.5-fast/net/socket.c 2012-07-19 03:05:36.000000000 +0200
> @@ -522,7 +522,9 @@ void sock_release(struct socket *sock)
> if (rcu_dereference_protected(sock->wq, 1)->fasync_list)
> printk(KERN_ERR "sock_release: fasync list not empty!\n");
>
> - percpu_sub(sockets_in_use, 1);
> + /* a hack - sockets_in_use should not be decremented when tun calls this */
> + if (sock->file != (void *)1)
> + percpu_sub(sockets_in_use, 1);
> if (!sock->file) {
> iput(SOCK_INODE(sock));
> return;
>
> ---
>
> BUG: unable to handle kernel NULL pointer dereference at 0000000000000020
> IP: [<ffffffff81113246>] iput+0x76/0x230
> PGD 43e5e9067 PUD 4468d5067 PMD 0
> Oops: 0000 [#1] PREEMPT SMP
> CPU 1
> Modules linked in: ip6table_filter ip6_tables iptable_filter ip_tables
> ebtable_nat ebtables x_tables kvm_amd kvm tun cpufreq_userspace
> cpufreq_stats cpufreq_powersave cpufreq_ondemand cpufreq_conservative ipv6
> fuse raid0 md_mod lm85 hwmon_vid snd_usb_audio snd_pcm_oss snd_mixer_oss
> snd_pcm snd_timer snd_page_alloc snd_hwdep snd_usbmidi_lib snd_rawmidi snd
> soundcore ide_cd_mod cdrom ohci_hcd sata_svw libata serverworks ide_core
> powernow_k8 ehci_hcd usbcore tg3 usb_common floppy freq_table e100 skge
> mii i2c_piix4 libphy mperf k10temp rtc_cmos processor button hwmon
> microcode unix
>
> Pid: 10826, comm: miredo Not tainted 3.4.5 #85 empty empty/S3992-E
> RIP: 0010:[<ffffffff81113246>] [<ffffffff81113246>] iput+0x76/0x230
> RSP: 0018:ffff88043dc73e48 EFLAGS: 00010246
> RAX: 0000000000000001 RBX: ffff88023eba3f20 RCX: ffff880447d80000
> RDX: 0000000000000001 RSI: ffff88023eba3f98 RDI: ffff88023eba3f98
> RBP: ffff88023eba3f98 R08: ffffffff814804d8 R09: 0000000000000000
> R10: 0000000000000096 R11: dead000000100100 R12: ffff88023eba3f48
> R13: 0000000000000000 R14: ffff88043dc73e88 R15: 00000000ffffad3a
> FS: 00007fe71bbb9700(0000) GS:ffff880247c80000(0000)
> knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> CR2: 0000000000000020 CR3: 000000043dcf0000 CR4: 00000000000007f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> Process miredo (pid: 10826, threadinfo ffff88043dc72000, task
> ffff88043dc1b8d0) Stack:
> ffff88043dc73e88 ffff88023efef000 ffff88023eba3800 ffff88023eba3c00
> ffff88024749ecc0 ffffffff81281d93 ffff88023e8fa500 ffffffff81295438
> ffff88043dc73e88 ffff88043dc73e88 ffff88023eba38f8 ffff88023e8fa500
> Call Trace:
> [<ffffffff81281d93>] ? sk_release_kernel+0x23/0x40
> [<ffffffff81295438>] ? netdev_run_todo+0x1a8/0x260
> [<ffffffffa02522a3>] ? tun_chr_close+0x93/0xb0 [tun]
> [<ffffffff810fc3ed>] ? fput+0xdd/0x260
> [<ffffffff810f8aff>] ? filp_close+0x5f/0x90
> [<ffffffff810f8bc7>] ? sys_close+0x97/0x100
> [<ffffffff81311f22>] ? system_call_fastpath+0x16/0x1b
> Code: 6c 24 10 4c 8b 64 24 18 4c 8b 6c 24 20 48 83 c4 28 c3 0f 1f 00 f6 83
> 90 00 00 00 08 4c 8b 63 28 4d 8b 6c 24 30 0f 85 7d 01 00 00 <49> 8b 45 20
> 48 85 c0 0f 84 9d 00 00 00 48 89 df ff d0 85 c0 0f
> RIP [<ffffffff81113246>] iput+0x76/0x230
> RSP <ffff88043dc73e48>
> CR2: 0000000000000020
> ---[ end trace 6bd5160ffd3ba7a2 ]---
> note: miredo[10826] exited with preempt_count 1
Hi Mikulas
A fix for this problem is : http://patchwork.ozlabs.org/patch/170440/
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