| From | Ben Hutchings <> | Date | Mon, 14 Nov 2016 00:14:20 +0000 | Subject | [PATCH 3.16 031/346] ext4: check for extents that wrap around |
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3.16.39-rc1 review patch. If anyone has any objections, please let me know.
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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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