ext4: check for extents that wrap around
authorVegard Nossum <vegard.nossum@oracle.com>
Thu, 30 Jun 2016 15:53:46 +0000 (11:53 -0400)
committerTheodore Ts'o <tytso@mit.edu>
Thu, 30 Jun 2016 15:53:46 +0000 (11:53 -0400)
commitf70749ca42943faa4d4dcce46dfdcaadb1d0c4b6
treef4f3877c9b353fb99102c10f9ac200739bb94e97
parentabcfb5d979892fc8b12574551fc907c05fe1b11b
ext4: check for extents that wrap around

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>
Cc: stable@vger.kernel.org
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>
fs/ext4/extents.c