ext4: reject too-large filesystems on 32-bit kernels

ext4 will happily mount a > 16T filesystem on a 32-bit box, but
this is not safe; writes to the block device will wrap past 16T
and the page cache can't index past 16T (232 index * 4k pages).

Adding another test to the existing "too many sectors" test
should do the trick.

Add a comment, a relevant return value, and fix the reference
to the CONFIG_LBD(AF) option as well.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 10 insertions, 3 deletions

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index fe3f376b7df2..de67c3657b83 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2550,12 +2550,19 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
                 goto failed_mount;
         }
 
-        if (ext4_blocks_count(es) >
-                    (sector_t)(~0ULL) >> (sb->s_blocksize_bits - 9)) {
+        /*
+         * Test whether we have more sectors than will fit in sector_t,
+         * and whether the max offset is addressable by the page cache.
+         */
+        if ((ext4_blocks_count(es) >
+             (sector_t)(~0ULL) >> (sb->s_blocksize_bits - 9)) ||
+            (ext4_blocks_count(es) >
+             (pgoff_t)(~0ULL) >> (PAGE_CACHE_SHIFT - sb->s_blocksize_bits))) {
                 ext4_msg(sb, KERN_ERR, "filesystem"
-                        " too large to mount safely");
+                         " too large to mount safely on this system");
                 if (sizeof(sector_t) < 8)
                         ext4_msg(sb, KERN_WARNING, "CONFIG_LBDAF not enabled");
+                ret = -EFBIG;
                 goto failed_mount;
         }