ext4: check for overlapping extents in ext4_valid_extent_entries()

commit 5946d089379a35dda0e531710b48fca05446a196 upstream.

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>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 3e8fc80..4b17307 100644 (file)
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -318,8 +318,10 @@ 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);
 }
@@ -345,11 +347,26 @@ 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);