hugetlbfs: handle empty options string

I was seeing a null pointer deref in fs/super.c:vfs_kern_mount().
Some file system get_sb() handler was returning NULL mnt_sb with
a non-negative return value.  I also noticed a "hugetlbfs: Bad
mount option:" message in the log.

Turns out that hugetlbfs_parse_options() was not checking for an
empty option string after call to strsep().  On failure,
hugetlbfs_parse_options() returns 1.  hugetlbfs_fill_super() just
passed this return code back up the call stack where
vfs_kern_mount() missed the error and proceeded with a NULL mnt_sb.

Apparently introduced by patch:
	hugetlbfs-use-lib-parser-fix-docs.patch

The problem was exposed by this line in my fstab:

none        /huge       hugetlbfs   defaults    0 0

It can also be demonstrated by invoking mount of hugetlbfs
directly with no options or a bogus option.

This patch:

1) adds the check for empty option to hugetlbfs_parse_options(),
2) enhances the error message to bracket any unrecognized
   option with quotes ,
3) modifies hugetlbfs_parse_options() to return -EINVAL on any
   unrecognized option,
4) adds a BUG_ON() to vfs_kern_mount() to catch any get_sb()
   handler that returns a NULL mnt->mnt_sb with a return value
   >= 0.

Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
Acked-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 6 insertions, 3 deletions

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 711b801fbcdf..d145cb79c30a 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -621,6 +621,8 @@ hugetlbfs_parse_options(char *options, struct hugetlbfs_config *pconfig)
 
         while ((p = strsep(&options, ",")) != NULL) {
                 int token;
+                if (!*p)
+                        continue;
 
                 token = match_token(p, tokens, args);
                 switch (token) {
@@ -665,8 +667,9 @@ hugetlbfs_parse_options(char *options, struct hugetlbfs_config *pconfig)
                         break;
 
                 default:
-                        printk(KERN_ERR "hugetlbfs: Bad mount option: %s\n", p);
-                        return 1;
+                        printk(KERN_ERR "hugetlbfs: Bad mount option: \"%s\"\n",
+                                 p);
+                        return -EINVAL;
                         break;
                 }
         }
@@ -693,7 +696,6 @@ hugetlbfs_fill_super(struct super_block *sb, void *data, int silent)
         config.gid = current->fsgid;
         config.mode = 0755;
         ret = hugetlbfs_parse_options(data, &config);
-
         if (ret)
                 return ret;
 
diff --git a/fs/super.c b/fs/super.c
index 5260d620c555..fc8ebedc6bed 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -884,6 +884,7 @@ vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void
         error = type->get_sb(type, flags, name, data, mnt);
         if (error < 0)
                 goto out_free_secdata;
+        BUG_ON(!mnt->mnt_sb);
 
         error = security_sb_kern_mount(mnt->mnt_sb, secdata);
         if (error)