md: raid5: avoid string overflow warning
authorArnd Bergmann <arnd@arndb.de>
Tue, 20 Feb 2018 13:09:11 +0000 (14:09 +0100)
committerShaohua Li <sh.li@alibaba-inc.com>
Wed, 21 Feb 2018 17:49:15 +0000 (09:49 -0800)
gcc warns about a possible overflow of the kmem_cache string, when adding
four characters to a string of the same length:

drivers/md/raid5.c: In function 'setup_conf':
drivers/md/raid5.c:2207:34: error: '-alt' directive writing 4 bytes into a region of size between 1 and 32 [-Werror=format-overflow=]
  sprintf(conf->cache_name[1], "%s-alt", conf->cache_name[0]);
                                  ^~~~
drivers/md/raid5.c:2207:2: note: 'sprintf' output between 5 and 36 bytes into a destination of size 32
  sprintf(conf->cache_name[1], "%s-alt", conf->cache_name[0]);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

If I'm counting correctly, we need 11 characters for the fixed part
of the string and 18 characters for a 64-bit pointer (when no gendisk
is used), so that leaves three characters for conf->level, which should
always be sufficient.

This makes the code use snprintf() with the correct length, to
make the code more robust against changes, and to get the compiler
to shut up.

In commit f4be6b43f1ac ("md/raid5: ensure we create a unique name for
kmem_cache when mddev has no gendisk") from 2010, Neil said that
the pointer could be removed "shortly" once devices without gendisk
are disallowed. I have no idea if that happened, but if it did, that
should probably be changed as well.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Shaohua Li <sh.li@alibaba-inc.com>
drivers/md/raid5.c

index 36e050678f5a533fdae36fb920b5113956dde88a..e3b0f799fbfae4cf985e421161002227d13bfd47 100644 (file)
@@ -2196,15 +2196,16 @@ static int grow_one_stripe(struct r5conf *conf, gfp_t gfp)
 static int grow_stripes(struct r5conf *conf, int num)
 {
        struct kmem_cache *sc;
 static int grow_stripes(struct r5conf *conf, int num)
 {
        struct kmem_cache *sc;
+       size_t namelen = sizeof(conf->cache_name[0]);
        int devs = max(conf->raid_disks, conf->previous_raid_disks);
 
        if (conf->mddev->gendisk)
        int devs = max(conf->raid_disks, conf->previous_raid_disks);
 
        if (conf->mddev->gendisk)
-               sprintf(conf->cache_name[0],
+               snprintf(conf->cache_name[0], namelen,
                        "raid%d-%s", conf->level, mdname(conf->mddev));
        else
                        "raid%d-%s", conf->level, mdname(conf->mddev));
        else
-               sprintf(conf->cache_name[0],
+               snprintf(conf->cache_name[0], namelen,
                        "raid%d-%p", conf->level, conf->mddev);
                        "raid%d-%p", conf->level, conf->mddev);
-       sprintf(conf->cache_name[1], "%s-alt", conf->cache_name[0]);
+       snprintf(conf->cache_name[1], namelen, "%.27s-alt", conf->cache_name[0]);
 
        conf->active_name = 0;
        sc = kmem_cache_create(conf->cache_name[conf->active_name],
 
        conf->active_name = 0;
        sc = kmem_cache_create(conf->cache_name[conf->active_name],