2018-02-16 22:13:27

by Alexey Khoroshilov

Subject: [PATCH] tun: fix mismatch in mutex lock-unlock in tun_get_user()

There is a single error path where tfile->napi_mutex is left unlocked.
It can lead to a deadlock.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <[email protected]>
---
drivers/net/tun.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 81e6cc951e7f..0072a9832532 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1879,6 +1879,10 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
default:
this_cpu_inc(tun->pcpu_stats->rx_dropped);
kfree_skb(skb);
+ if (frags) {
+ tfile->napi.skb = NULL;
+ mutex_unlock(&tfile->napi_mutex);
+ }
return -EINVAL;
}
}
--
2.7.4

2018-02-16 22:45:27

by Eric Dumazet

Subject: Re: [PATCH] tun: fix mismatch in mutex lock-unlock in tun_get_user()

On Fri, Feb 16, 2018 at 2:11 PM, Alexey Khoroshilov
<[email protected]> wrote:
> There is a single error path where tfile->napi_mutex is left unlocked.
> It can lead to a deadlock.
>
> Found by Linux Driver Verification project (linuxtesting.org).
>
> Signed-off-by: Alexey Khoroshilov <[email protected]>
> ---
> drivers/net/tun.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 81e6cc951e7f..0072a9832532 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -1879,6 +1879,10 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
> default:
> this_cpu_inc(tun->pcpu_stats->rx_dropped);
> kfree_skb(skb);
> + if (frags) {
> + tfile->napi.skb = NULL;
> + mutex_unlock(&tfile->napi_mutex);
> + }
> return -EINVAL;


I do not believe this can happen for IFF_TUN

IFF_NAPI_FRAGS can only be set for IFF_TAP

2018-02-19 16:15:58

by David Miller

Subject: Re: [PATCH] tun: fix mismatch in mutex lock-unlock in tun_get_user()

From: Alexey Khoroshilov <[email protected]>
Date: Sat, 17 Feb 2018 01:11:55 +0300

> There is a single error path where tfile->napi_mutex is left unlocked.
> It can lead to a deadlock.
>
> Found by Linux Driver Verification project (linuxtesting.org).
>
> Signed-off-by: Alexey Khoroshilov <[email protected]>

As Eric explained, tun_napi_frags_enabled() (and therefore 'frags')
will never be true for TUN devices, which is the type handled by this
code path.