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ext4: prevent right-shifting extents beyond EXT_MAX_BLOCKS

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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>
This commit is contained in:
Eric Biggers 2018-04-12 11:48:09 -04:00 committed by Theodore Ts'o
parent e40ff21389
commit 349fa7d6e1
1 changed files with 11 additions and 5 deletions
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16
fs/ext4/extents.c
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@ -5329,8 +5329,9 @@ ext4_ext_shift_extents(struct inode *inode, handle_t *handle,
stop = le32_to_cpu(extent->ee_block);
/*
* In case of left shift, Don't start shifting extents until we make
* sure the hole is big enough to accommodate the shift.
* For left shifts, make sure the hole on the left is big enough to
* accommodate the shift. For right shifts, make sure the last extent
* won't be shifted beyond EXT_MAX_BLOCKS.
*/
if (SHIFT == SHIFT_LEFT) {
path = ext4_find_extent(inode, start - 1, &path,
@ -5350,9 +5351,14 @@ ext4_ext_shift_extents(struct inode *inode, handle_t *handle,
if ((start == ex_start && shift > ex_start) ||
(shift > start - ex_end)) {
ext4_ext_drop_refs(path);
kfree(path);
return -EINVAL;
ret = -EINVAL;
goto out;
}
} else {
if (shift > EXT_MAX_BLOCKS -
(stop + ext4_ext_get_actual_len(extent))) {
ret = -EINVAL;
goto out;
}
}