cgroup: make the mount options parsing more accurate

Current behavior:
=================

(1) When we mount a cgroup, we can specify the 'all' option which
    means to enable all the cgroup subsystems.  This is the default option
    when no option is specified.

(2) If we want to mount a cgroup with a subset of the supported cgroup
    subsystems, we have to specify a subsystems name list for the mount
    option.

(3) If we specify another option like 'noprefix' or 'release_agent',
    the actual code wants the 'all' or a subsystem name option specified
    also.  Not critical but a bit not friendly as we should assume (1) in
    this case.

(4) Logically, the 'all' option is mutually exclusive with a subsystem
    name, but this is not detected.

In other words:
 succeed : mount -t cgroup -o all,freezer cgroup /cgroup
	=> is it 'all' or 'freezer' ?
 fails : mount -t cgroup -o noprefix cgroup /cgroup
	=> succeed if we do '-o noprefix,all'

The following patches consolidate a bit the mount options check.

New behavior:
=============

(1) untouched
(2) untouched
(3) the 'all' option will be by default when specifying other than
    a subsystem name option
(4) raises an error

In other words:
 fails   : mount -t cgroup -o all,freezer cgroup /cgroup
 succeed : mount -t cgroup -o noprefix cgroup /cgroup

For the sake of lisibility, the if ... then ... else ... if ...
indentation when parsing the options has been changed to:
if ... then
	...
	continue
fi

Signed-off-by: Daniel Lezcano <daniel.lezcano@free.fr>
Signed-off-by: Serge E. Hallyn <serge.hallyn@canonical.com>
Reviewed-by: Li Zefan <lizf@cn.fujitsu.com>
Reviewed-by: Paul Menage <menage@google.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Jamal Hadi Salim <hadi@cyberus.ca>
Cc: Matt Helsley <matthltc@us.ibm.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 60 insertions, 30 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 4b218a46ddd3..3e6517e51fd3 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1074,7 +1074,8 @@ struct cgroup_sb_opts {
  */
 static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
 {
-        char *token, *o = data ?: "all";
+        char *token, *o = data;
+        bool all_ss = false, one_ss = false;
         unsigned long mask = (unsigned long)-1;
         int i;
         bool module_pin_failed = false;
@@ -1090,24 +1091,27 @@ static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
         while ((token = strsep(&o, ",")) != NULL) {
                 if (!*token)
                         return -EINVAL;
-                if (!strcmp(token, "all")) {
-                        /* Add all non-disabled subsystems */
-                        opts->subsys_bits = 0;
-                        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
-                                struct cgroup_subsys *ss = subsys[i];
-                                if (ss == NULL)
-                                        continue;
-                                if (!ss->disabled)
-                                        opts->subsys_bits |= 1ul << i;
-                        }
-                } else if (!strcmp(token, "none")) {
+                if (!strcmp(token, "none")) {
                         /* Explicitly have no subsystems */
                         opts->none = true;
-                } else if (!strcmp(token, "noprefix")) {
+                        continue;
+                }
+                if (!strcmp(token, "all")) {
+                        /* Mutually exclusive option 'all' + subsystem name */
+                        if (one_ss)
+                                return -EINVAL;
+                        all_ss = true;
+                        continue;
+                }
+                if (!strcmp(token, "noprefix")) {
                         set_bit(ROOT_NOPREFIX, &opts->flags);
-                } else if (!strcmp(token, "clone_children")) {
+                        continue;
+                }
+                if (!strcmp(token, "clone_children")) {
                         opts->clone_children = true;
-                } else if (!strncmp(token, "release_agent=", 14)) {
+                        continue;
+                }
+                if (!strncmp(token, "release_agent=", 14)) {
                         /* Specifying two release agents is forbidden */
                         if (opts->release_agent)
                                 return -EINVAL;
@@ -1115,7 +1119,9 @@ static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
                                 kstrndup(token + 14, PATH_MAX - 1, GFP_KERNEL);
                         if (!opts->release_agent)
                                 return -ENOMEM;
-                } else if (!strncmp(token, "name=", 5)) {
+                        continue;
+                }
+                if (!strncmp(token, "name=", 5)) {
                         const char *name = token + 5;
                         /* Can't specify an empty name */
                         if (!strlen(name))
@@ -1137,20 +1143,44 @@ static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
                                               GFP_KERNEL);
                         if (!opts->name)
                                 return -ENOMEM;
-                } else {
-                        struct cgroup_subsys *ss;
-                        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
-                                ss = subsys[i];
-                                if (ss == NULL)
-                                        continue;
-                                if (!strcmp(token, ss->name)) {
-                                        if (!ss->disabled)
-                                                set_bit(i, &opts->subsys_bits);
-                                        break;
-                                }
-                        }
-                        if (i == CGROUP_SUBSYS_COUNT)
-                                return -ENOENT;
+
+                        continue;
+                }
+
+                for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+                        struct cgroup_subsys *ss = subsys[i];
+                        if (ss == NULL)
+                                continue;
+                        if (strcmp(token, ss->name))
+                                continue;
+                        if (ss->disabled)
+                                continue;
+
+                        /* Mutually exclusive option 'all' + subsystem name */
+                        if (all_ss)
+                                return -EINVAL;
+                        set_bit(i, &opts->subsys_bits);
+                        one_ss = true;
+
+                        break;
+                }
+                if (i == CGROUP_SUBSYS_COUNT)
+                        return -ENOENT;
+        }
+
+        /*
+         * If the 'all' option was specified select all the subsystems,
+         * otherwise 'all, 'none' and a subsystem name options were not
+         * specified, let's default to 'all'
+         */
+        if (all_ss || (!all_ss && !one_ss && !opts->none)) {
+                for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+                        struct cgroup_subsys *ss = subsys[i];
+                        if (ss == NULL)
+                                continue;
+                        if (ss->disabled)
+                                continue;
+                        set_bit(i, &opts->subsys_bits);
                 }
         }