[PATCH] net: check all name nodes in __dev_alloc_name

[PATCH] net: check all name nodes in __dev_alloc_name

[Jiri Bohac]

__dev_alloc_name(), when supplied with a name containing '%d',
will search for the first available device number to generate a
unique device name.

Since commit ff92741270bf8b6e78aa885f166b68c7a67ab13a ("net:
introduce name_node struct to be used in hashlist") network
devices may have alternate names.  __dev_alloc_name() does take
these alternate names into account, possibly generating a name
that is already taken and failing with -ENFILE as a result.

This demonstrates the bug:

    # rmmod dummy 2>/dev/null
    # ip link property add dev lo altname dummy0
    # modprobe dummy numdummies=1
    modprobe: ERROR: could not insert 'dummy': Too many open files in system

Instead of creating a device named dummy1, modprobe fails.

Fix this by checking all the names in the d->name_node list, not just d->name.

Signed-off-by: Jiri Bohac <jbohac@suse.cz>
Fixes: ff92741270bf ("net: introduce name_node struct to be used in hashlist")

diff --git a/net/core/dev.c b/net/core/dev.c
index 6c5967e80132..7cbcd8d37e91 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1184,6 +1184,18 @@ static int __dev_alloc_name(struct net *net, const char *name, char *buf)
 			return -ENOMEM;
 
 		for_each_netdev(net, d) {
+			struct netdev_name_node *name_node;
+			list_for_each_entry(name_node, &d->name_node->list, list) {
+				if (!sscanf(name_node->name, name, &i))
+					continue;
+				if (i < 0 || i >= max_netdevices)
+					continue;
+
+				/*  avoid cases where sscanf is not exact inverse of printf */
+				snprintf(buf, IFNAMSIZ, name, i);
+				if (!strncmp(buf, name_node->name, IFNAMSIZ))
+					set_bit(i, inuse);
+			}
 			if (!sscanf(d->name, name, &i))
 				continue;
 			if (i < 0 || i >= max_netdevices)

-- 
Jiri Bohac <jbohac@suse.cz>
SUSE Labs, Prague, Czechia

Re: [PATCH] net: check all name nodes in __dev_alloc_name

[Stephen Hemminger]

On Thu, 18 Mar 2021 04:42:53 +0100
Jiri Bohac <jbohac@suse.cz> wrote:

>  		for_each_netdev(net, d) {
> +			struct netdev_name_node *name_node;
> +			list_for_each_entry(name_node, &d->name_node->list, list) {
> +				if (!sscanf(name_node->name, name, &i))
> +					continue;
> +				if (i < 0 || i >= max_netdevices)
> +					continue;
> +
> +				/*  avoid cases where sscanf is not exact inverse of printf */
> +				snprintf(buf, IFNAMSIZ, name, i);
> +				if (!strncmp(buf, name_node->name, IFNAMSIZ))
> +					set_bit(i, inuse);
> +			}

Rather than copy/paste same code two places, why not make a helper function?

Re: [PATCH] net: check all name nodes in __dev_alloc_name

[Jiri Bohac]

On Wed, Mar 17, 2021 at 09:11:08PM -0700, Stephen Hemminger wrote:
> Rather than copy/paste same code two places, why not make a helper function?

I tried and in it was ugly (too many dependencies into the
currecnt function)

Another option I considered and scratched was to opencode and
modify list_for_each to also act on the dev->name_node
which contains the list head. Or maybe one of the
list_for_each_* variants could be directly misused for that.

I don't understand why this has been designed in such a
non-standard way; why is the first node not part of the list and
the head directly in the net_device?

In the end I considered the copy'n'paste of 9 lines the least
ugly and most readable.

-- 
Jiri Bohac <jbohac@suse.cz>
SUSE Labs, Prague, Czechia

Re: [PATCH] net: check all name nodes in __dev_alloc_name

[Stephen Hemminger]

On Thu, 18 Mar 2021 10:06:52 +0100
Jiri Bohac <jbohac@suse.cz> wrote:

> On Wed, Mar 17, 2021 at 09:11:08PM -0700, Stephen Hemminger wrote:
> > Rather than copy/paste same code two places, why not make a helper function?  
> 
> I tried and in it was ugly (too many dependencies into the
> currecnt function)
> 
> Another option I considered and scratched was to opencode and
> modify list_for_each to also act on the dev->name_node
> which contains the list head. Or maybe one of the
> list_for_each_* variants could be directly misused for that.

That seems like overly complex and unhelpful option.

> I don't understand why this has been designed in such a
> non-standard way; why is the first node not part of the list and
> the head directly in the net_device?
> 
> In the end I considered the copy'n'paste of 9 lines the least
> ugly and most readable.
> 

Sure, make sense.

Re: [PATCH] net: check all name nodes in __dev_alloc_name

[Jiri Pirko]

Thu, Mar 18, 2021 at 04:42:53AM CET, jbohac@suse.cz wrote:
>__dev_alloc_name(), when supplied with a name containing '%d',
>will search for the first available device number to generate a
>unique device name.
>
>Since commit ff92741270bf8b6e78aa885f166b68c7a67ab13a ("net:
>introduce name_node struct to be used in hashlist") network
>devices may have alternate names.  __dev_alloc_name() does take
>these alternate names into account, possibly generating a name
>that is already taken and failing with -ENFILE as a result.
>
>This demonstrates the bug:
>
>    # rmmod dummy 2>/dev/null
>    # ip link property add dev lo altname dummy0
>    # modprobe dummy numdummies=1
>    modprobe: ERROR: could not insert 'dummy': Too many open files in system
>
>Instead of creating a device named dummy1, modprobe fails.
>
>Fix this by checking all the names in the d->name_node list, not just d->name.
>
>Signed-off-by: Jiri Bohac <jbohac@suse.cz>
>Fixes: ff92741270bf ("net: introduce name_node struct to be used in hashlist")

Reviewed-by: Jiri Pirko <jiri@nvidia.com>

Thanks!

Re: [PATCH] net: check all name nodes in __dev_alloc_name

[Andrew Lunn]

On Thu, Mar 18, 2021 at 04:42:53AM +0100, Jiri Bohac wrote:
> __dev_alloc_name(), when supplied with a name containing '%d',
> will search for the first available device number to generate a
> unique device name.
> 
> Since commit ff92741270bf8b6e78aa885f166b68c7a67ab13a ("net:
> introduce name_node struct to be used in hashlist") network
> devices may have alternate names.  __dev_alloc_name() does take

Should this be "does not take"

> these alternate names into account, possibly generating a name
> that is already taken and failing with -ENFILE as a result.

  Andrew

Re: [PATCH] net: check all name nodes in __dev_alloc_name

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (refs/heads/master):

On Thu, 18 Mar 2021 04:42:53 +0100 you wrote:
> __dev_alloc_name(), when supplied with a name containing '%d',
> will search for the first available device number to generate a
> unique device name.
> 
> Since commit ff92741270bf8b6e78aa885f166b68c7a67ab13a ("net:
> introduce name_node struct to be used in hashlist") network
> devices may have alternate names.  __dev_alloc_name() does take
> these alternate names into account, possibly generating a name
> that is already taken and failing with -ENFILE as a result.
> 
> [...]

Here is the summary with links:
  - net: check all name nodes in __dev_alloc_name
    https://git.kernel.org/netdev/net/c/6c015a225680

You are awesome, thank you!
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