fs/minix: Verify bitmap block counts before mounting

Newer versions of MINIX can create filesystems that allocate an extra
bitmap block.  Mounting of this succeeds, but doing a statfs call will
result in an oops in count_free because of a negative number being used
for the bh index.

Avoid this by verifying the number of allocated blocks at mount time,
erroring out if there are not enough and make statfs ignore the extras
if there are too many.

This fixes https://bugzilla.kernel.org/show_bug.cgi?id=18792

Signed-off-by: Josh Boyer <jwboyer@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 23 insertions, 2 deletions

diff --git a/fs/minix/inode.c b/fs/minix/inode.c
index 64cdcd662ffc..1d9e33966db0 100644
--- a/fs/minix/inode.c
+++ b/fs/minix/inode.c
@@ -279,6 +279,27 @@ static int minix_fill_super(struct super_block *s, void *data, int silent)
         else if (sbi->s_mount_state & MINIX_ERROR_FS)
                 printk("MINIX-fs: mounting file system with errors, "
                         "running fsck is recommended\n");
+
+        /* Apparently minix can create filesystems that allocate more blocks for
+         * the bitmaps than needed.  We simply ignore that, but verify it didn't
+         * create one with not enough blocks and bail out if so.
+         */
+        block = minix_blocks_needed(sbi->s_ninodes, s->s_blocksize);
+        if (sbi->s_imap_blocks < block) {
+                printk("MINIX-fs: file system does not have enough "
+                                "imap blocks allocated.  Refusing to mount\n");
+                goto out_iput;
+        }
+
+        block = minix_blocks_needed(
+                        (sbi->s_nzones - (sbi->s_firstdatazone + 1)),
+                        s->s_blocksize);
+        if (sbi->s_zmap_blocks < block) {
+                printk("MINIX-fs: file system does not have enough "
+                                "zmap blocks allocated.  Refusing to mount.\n");
+                goto out_iput;
+        }
+
         return 0;
 
 out_iput:
@@ -339,10 +360,10 @@ static int minix_statfs(struct dentry *dentry, struct kstatfs *buf)
         buf->f_type = sb->s_magic;
         buf->f_bsize = sb->s_blocksize;
         buf->f_blocks = (sbi->s_nzones - sbi->s_firstdatazone) << sbi->s_log_zone_size;
-        buf->f_bfree = minix_count_free_blocks(sbi);
+        buf->f_bfree = minix_count_free_blocks(sb);
         buf->f_bavail = buf->f_bfree;
         buf->f_files = sbi->s_ninodes;
-        buf->f_ffree = minix_count_free_inodes(sbi);
+        buf->f_ffree = minix_count_free_inodes(sb);
         buf->f_namelen = sbi->s_namelen;
         buf->f_fsid.val[0] = (u32)id;
         buf->f_fsid.val[1] = (u32)(id >> 32);