[PATCH] reject too-large filesystems on 32-bit kernels

[Eric Sandeen <sandeen@redhat.com>]

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 (2^32 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>
---

Index: linux-2.6.29.noarch/fs/ext4/super.c
===================================================================
--- linux-2.6.29.noarch.orig/fs/ext4/super.c
+++ linux-2.6.29.noarch/fs/ext4/super.c
@@ -2274,13 +2274,20 @@ static int ext4_fill_super(struct super_
 		goto failed_mount;
 	}
 
+	/*
+	 * 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)) {
+		    (sector_t)(~0ULL) >> (sb->s_blocksize_bits - 9) ||
+	    ext4_blocks_count(es) >
+		    (pgoff_t)(~0ULL) >> (PAGE_CACHE_SHIFT - sb->s_blocksize_bits)) {
 		printk(KERN_ERR "EXT4-fs: filesystem on %s:"
-			" too large to mount safely\n", sb->s_id);
+			" too large to mount safely on this system\n", sb->s_id);
 		if (sizeof(sector_t) < 8)
-			printk(KERN_WARNING "EXT4-fs: CONFIG_LBD not "
+			printk(KERN_WARNING "EXT4-fs: CONFIG_LBDAF not "
 					"enabled\n");
+		ret = EFBIG;
 		goto failed_mount;
 	}