[PATCH 4.4 077/101] ext4: fix EXT_MAX_EXTENT/INDEX to check for zeroed eh_max

Greg Kroah-Hartman
2020-06-19T14:38:45Z

From: Harshad Shirwadkar <harshadshirwadkar@gmail.com>

commit c36a71b4e35ab35340facdd6964a00956b9fef0a upstream.

If eh->eh_max is 0, EXT_MAX_EXTENT/INDEX would evaluate to unsigned
(-1) resulting in illegal memory accesses. Although there is no
consistent repro, we see that generic/019 sometimes crashes because of
this bug.

Ran gce-xfstests smoke and verified that there were no regressions.

Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@gmail.com>
Link: https://lore.kernel.org/r/20200421023959.20879-2-harshadshirwadkar@gmail.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/ext4/ext4_extents.h | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)

--- a/fs/ext4/ext4_extents.h
+++ b/fs/ext4/ext4_extents.h
@@ -169,10 +169,13 @@ struct ext4_ext_path {
(EXT_FIRST_EXTENT((__hdr__)) + le16_to_cpu((__hdr__)->eh_entries) - 1)
#define EXT_LAST_INDEX(__hdr__) \
(EXT_FIRST_INDEX((__hdr__)) + le16_to_cpu((__hdr__)->eh_entries) - 1)
-#define EXT_MAX_EXTENT(__hdr__) \
- (EXT_FIRST_EXTENT((__hdr__)) + le16_to_cpu((__hdr__)->eh_max) - 1)
+#define EXT_MAX_EXTENT(__hdr__) \
+ ((le16_to_cpu((__hdr__)->eh_max)) ? \
+ ((EXT_FIRST_EXTENT((__hdr__)) + le16_to_cpu((__hdr__)->eh_max) - 1)) \
+ : 0)
#define EXT_MAX_INDEX(__hdr__) \
- (EXT_FIRST_INDEX((__hdr__)) + le16_to_cpu((__hdr__)->eh_max) - 1)
+ ((le16_to_cpu((__hdr__)->eh_max)) ? \
+ ((EXT_FIRST_INDEX((__hdr__)) + le16_to_cpu((__hdr__)->eh_max) - 1)) : 0)

static inline struct ext4_extent_header *ext_inode_hdr(struct inode *inode)
{