cgroups: forbid noprefix if mounting more than just cpuset subsystem

The 'noprefix' option was introduced for backwards-compatibility of
cpuset, but actually it can be used when mounting other subsystems.

This results in possibility of name collision, and now the collision can
really happen, because we have 'stat' file in both memory and cpuacct
subsystem:

	# mount -t cgroup -o noprefix,memory,cpuacct xxx /mnt

Cgroup will happily mount the 2 subsystems, but only 'stat' file of memory
subsys can be seen.

We don't want users to use nopreifx, and also want to avoid name
collision, so we change to allow noprefix only if mounting just the cpuset
subsystem.

[akpm@linux-foundation.org: fix shift for cpuset_subsys_id >= 32]
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: Dhaval Giani <dhaval@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 3fb789f6df9431073c815939dac2015d04e705d6..3737a682cdf52229ee78efa5c637164ba60dcc28 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -843,6 +843,11 @@ static int parse_cgroupfs_options(char *data,
                                     struct cgroup_sb_opts *opts)
 {
        char *token, *o = data ?: "all";
+       unsigned long mask = (unsigned long)-1;
+
+#ifdef CONFIG_CPUSETS
+       mask = ~(1UL << cpuset_subsys_id);
+#endif
 
        opts->subsys_bits = 0;
        opts->flags = 0;
@@ -887,6 +892,15 @@ static int parse_cgroupfs_options(char *data,
                }
        }
 
+       /*
+        * Option noprefix was introduced just for backward compatibility
+        * with the old cpuset, so we allow noprefix only if mounting just
+        * the cpuset subsystem.
+        */
+       if (test_bit(ROOT_NOPREFIX, &opts->flags) &&
+           (opts->subsys_bits & mask))
+               return -EINVAL;
+
        /* We can't have an empty hierarchy */
        if (!opts->subsys_bits)
                return -EINVAL;