ext4: check for overlapping extents in ext4_valid_extent_entries()

A corrupted ext4 may have out of order leaf extents, i.e.

extent: lblk 0--1023, len 1024, pblk 9217, flags: LEAF UNINIT
extent: lblk 1000--2047, len 1024, pblk 10241, flags: LEAF UNINIT
             ^^^^ overlap with previous extent

Reading such extent could hit BUG_ON() in ext4_es_cache_extent().

	BUG_ON(end < lblk);

The problem is that __read_extent_tree_block() tries to cache holes as
well but assumes 'lblk' is greater than 'prev' and passes underflowed
length to ext4_es_cache_extent(). Fix it by checking for overlapping
extents in ext4_valid_extent_entries().

I hit this when fuzz testing ext4, and am able to reproduce it by
modifying the on-disk extent by hand.

Also add the check for (ee_block + len - 1) in ext4_valid_extent() to
make sure the value is not overflow.

Ran xfstests on patched ext4 and no regression.

Cc: Lukáš Czerner <lczerner@redhat.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@vger.kernel.org

1 files changed, 18 insertions, 1 deletions

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 35f65cf4f318..267c9fb53bf9 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -360,8 +360,10 @@ static int ext4_valid_extent(struct inode *inode, struct ext4_extent *ext)
 {
         ext4_fsblk_t block = ext4_ext_pblock(ext);
         int len = ext4_ext_get_actual_len(ext);
+        ext4_lblk_t lblock = le32_to_cpu(ext->ee_block);
+        ext4_lblk_t last = lblock + len - 1;
 
-        if (len == 0)
+        if (lblock > last)
                 return 0;
         return ext4_data_block_valid(EXT4_SB(inode->i_sb), block, len);
 }
@@ -387,11 +389,26 @@ static int ext4_valid_extent_entries(struct inode *inode,
         if (depth == 0) {
                 /* leaf entries */
                 struct ext4_extent *ext = EXT_FIRST_EXTENT(eh);
+                struct ext4_super_block *es = EXT4_SB(inode->i_sb)->s_es;
+                ext4_fsblk_t pblock = 0;
+                ext4_lblk_t lblock = 0;
+                ext4_lblk_t prev = 0;
+                int len = 0;
                 while (entries) {
                         if (!ext4_valid_extent(inode, ext))
                                 return 0;
+
+                        /* Check for overlapping extents */
+                        lblock = le32_to_cpu(ext->ee_block);
+                        len = ext4_ext_get_actual_len(ext);
+                        if ((lblock <= prev) && prev) {
+                                pblock = ext4_ext_pblock(ext);
+                                es->s_last_error_block = cpu_to_le64(pblock);
+                                return 0;
+                        }
                         ext++;
                         entries--;
+                        prev = lblock + len - 1;
                 }
         } else {
                 struct ext4_extent_idx *ext_idx = EXT_FIRST_INDEX(eh);