V7: Adjust sanity checks for some volumes

Newly mkfs-ed filesystems from Seventh Edition have last modification
time set to zero, but are otherwise perfectly valid.

Also, tighten up other sanity checks to filter out most filesystems with
different bytesex than we're using.

Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

2 files changed, 15 insertions, 2 deletions

diff --git a/fs/sysv/super.c b/fs/sysv/super.c
index 2da3075aff78..5c0aab0b7e18 100644
--- a/fs/sysv/super.c
+++ b/fs/sysv/super.c
@@ -469,7 +469,7 @@ static int v7_fill_super(struct super_block *sb, void *data, int silent)
         v7sb = (struct v7_super_block *) bh->b_data;
         if (fs16_to_cpu(sbi, v7sb->s_nfree) > V7_NICFREE ||
             fs16_to_cpu(sbi, v7sb->s_ninode) > V7_NICINOD ||
-            fs32_to_cpu(sbi, v7sb->s_time) == 0)
+            fs32_to_cpu(sbi, v7sb->s_fsize) > V7_MAXSIZE)
                 goto failed;
 
         /* plausibility check on root inode: it is a directory,
@@ -479,7 +479,9 @@ static int v7_fill_super(struct super_block *sb, void *data, int silent)
         v7i = (struct sysv_inode *)(bh2->b_data + 64);
         if ((fs16_to_cpu(sbi, v7i->i_mode) & ~0777) != S_IFDIR ||
             (fs32_to_cpu(sbi, v7i->i_size) == 0) ||
-            (fs32_to_cpu(sbi, v7i->i_size) & 017) != 0)
+            (fs32_to_cpu(sbi, v7i->i_size) & 017) ||
+            (fs32_to_cpu(sbi, v7i->i_size) > V7_NFILES *
+             sizeof (struct sysv_dir_entry)))
                 goto failed;
         brelse(bh2);
         bh2 = NULL;
diff --git a/include/linux/sysv_fs.h b/include/linux/sysv_fs.h
index 96411306eec6..e47d6d90023d 100644
--- a/include/linux/sysv_fs.h
+++ b/include/linux/sysv_fs.h
@@ -148,6 +148,17 @@ struct v7_super_block {
         char    s_fname[6];     /* file system name */
         char    s_fpack[6];     /* file system pack name */
 };
+/* Constants to aid sanity checking */
+/* This is not a hard limit, nor enforced by v7 kernel. It's actually just
+ * the limit used by Seventh Edition's ls, though is high enough to assume
+ * that no reasonable file system would have that much entries in root
+ * directory. Thus, if we see anything higher, we just probably got the
+ * endiannes wrong. */
+#define V7_NFILES       1024
+/* The disk addresses are three-byte (despite direct block addresses being
+ * aligned word-wise in inode). If the most significant byte is non-zero,
+ * something is most likely wrong (not a filesystem, bad bytesex). */
+#define V7_MAXSIZE      0x00ffffff
 
 /* Coherent super-block data on disk */
 #define COH_NICINOD     100     /* number of inode cache entries */