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

[David Miller]

From: Alexey Khoroshilov 
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 

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.

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

[David Miller]

From: Alexey Khoroshilov 
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 

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.

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

[Eric Dumazet]

On Fri, Feb 16, 2018 at 2:11 PM, Alexey Khoroshilov
 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 
> ---
>  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(>napi_mutex);
> +   }
> return -EINVAL;


I do not believe this can happen for IFF_TUN

IFF_NAPI_FRAGS can only be set for IFF_TAP

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

[Eric Dumazet]

On Fri, Feb 16, 2018 at 2:11 PM, Alexey Khoroshilov
 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 
> ---
>  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(>napi_mutex);
> +   }
> return -EINVAL;


I do not believe this can happen for IFF_TUN

IFF_NAPI_FRAGS can only be set for IFF_TAP