On Tue, Apr 10, 2018 at 12:01:04AM -0700, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@xxxxxxxxxx>
>
> 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.
Could you please wrap this up into a xfstest for regression testing?
--D
> Reported-by: syzbot+06c885be0edcdaeab40c@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: 331573febb6a ("ext4: Add support FALLOC_FL_INSERT_RANGE for fallocate")
> Cc: <stable@xxxxxxxxxxxxxxx> # v4.2+
> Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
> ---
> fs/ext4/extents.c | 16 +++++++++++-----
> 1 file changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 0a7315961bac6..c969275ce3ee7 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -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;
> }
> }
>
> --
> 2.17.0
>
