During the "insert range" fallocate operation, extents starting at the
range offset are shifted "right" (to a higher file offset) by the range
length. But, as shown by syzbot, it's not validated that this doesn't
cause extents to be shifted beyond EXT_MAX_BLOCKS. In that case
->ee_block can wrap around, corrupting the extent tree.
Fix it by returning an error if the space between the end of the last
extent and EXT4_MAX_BLOCKS is smaller than the range being inserted.
This bug can be reproduced by running the following commands when the
current directory is on an ext4 filesystem with a 4k block size:
fallocate -l 8192 file
fallocate --keep-size -o 0xfffffffe000 -l 4096 -n file
fallocate --insert-range -l 8192 file
Then after unmounting the filesystem, e2fsck reports corruption.
Reported-by: syzbot+06c885be0edcdaeab40c@syzkaller.appspotmail.com
Fixes: 331573febb ("ext4: Add support FALLOC_FL_INSERT_RANGE for fallocate")
Cc: stable@vger.kernel.org # v4.2+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
349fa7d6e1