netdev - [PATCH] net: check all name nodes in __dev_alloc

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Date:   Thu, 18 Mar 2021 04:42:53 +0100
From:   Jiri Bohac <jbohac@...e.cz>
To:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        Jiri Pirko <jiri@...dia.com>
Subject: [PATCH] net: check all name nodes in  __dev_alloc_name

__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@...e.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@...e.cz>
SUSE Labs, Prague, Czechia