net: trust the bitmap in __dev_alloc_name()

Prior to restructuring __dev_alloc_name() handled both printf
and non-printf names. In a clever attempt at code reuse it
always prints the name into a buffer and checks if it's
a duplicate.

Trust the bitmap, and return an error if its full.

This shrinks the possible ID space by one from 32K to 32K - 1,
as previously the max value would have been tried as a valid ID.
It seems very unlikely that anyone would care as we heard
no requests to increase the max beyond 32k.

Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Link: https://lore.kernel.org/r/20231023152346.3639749-5-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/core/dev.c b/net/core/dev.c
index bbfb02b..d2698b4 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1119,18 +1119,11 @@ static int __dev_alloc_name(struct net *net, const char *name, char *res)
 
        i = find_first_zero_bit(inuse, max_netdevices);
        bitmap_free(inuse);
+       if (i == max_netdevices)
+               return -ENFILE;
 
-       snprintf(buf, IFNAMSIZ, name, i);
-       if (!netdev_name_in_use(net, buf)) {
-               strscpy(res, buf, IFNAMSIZ);
-               return i;
-       }
-
-       /* It is possible to run out of possible slots
-        * when the name is long and there isn't enough space left
-        * for the digits, or if all bits are used.
-        */
-       return -ENFILE;
+       snprintf(res, IFNAMSIZ, name, i);
+       return i;
 }
 
 /* Returns negative errno or allocated unit id (see __dev_alloc_name()) */