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Subject[PATCH 3.16 031/346] ext4: check for extents that wrap around
3.16.39-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Vegard Nossum <vegard.nossum@oracle.com>

commit f70749ca42943faa4d4dcce46dfdcaadb1d0c4b6 upstream.

An extent with lblock = 4294967295 and len = 1 will pass the
ext4_valid_extent() test:

ext4_lblk_t last = lblock + len - 1;

if (len == 0 || lblock > last)
return 0;

since last = 4294967295 + 1 - 1 = 4294967295. This would later trigger
the BUG_ON(es->es_lblk + es->es_len < es->es_lblk) in ext4_es_end().

We can simplify it by removing the - 1 altogether and changing the test
to use lblock + len <= lblock, since now if len = 0, then lblock + 0 ==
lblock and it fails, and if len > 0 then lblock + len > lblock in order
to pass (i.e. it doesn't overflow).

Fixes: 5946d0893 ("ext4: check for overlapping extents in ext4_valid_extent_entries()")
Fixes: 2f974865f ("ext4: check for zero length extent explicitly")
Cc: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Phil Turnbull <phil.turnbull@oracle.com>
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
fs/ext4/extents.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -359,9 +359,13 @@ static int ext4_valid_extent(struct inod
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 || lblock > last)
+ /*
+ * We allow neither:
+ * - zero length
+ * - overflow/wrap-around
+ */
+ if (lblock + len <= lblock)
return 0;
return ext4_data_block_valid(EXT4_SB(inode->i_sb), block, len);
}
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