From: BingJing Chang <[email protected]>
In commit d77815461f04 ("btrfs: Avoid trucating page or punching hole
in a already existed hole."), existed holes can be skipped by calling
find_first_non_hole() to adjust *start and *len. However, if the given
len is invalid and large, when an EXTENT_MAP_HOLE extent is found, the
*len will not be set to zero because (em->start + em->len) is less than
(*start + *len). Then the ret will be 1 but the *len will not be set to
0. The propagated non-zero ret will result in fallocate failure.
In the while-loop of btrfs_replace_file_extents(), len is not updated
every time before it calls find_first_non_hole(). That is, after
btrfs_drop_extents() successfully drops the last non-hole file extent,
it may fail with -ENOSPC when attempting to drop a file extent item
representing a hole. The problem can happen. After it calls
find_first_non_hole(), the cur_offset will be adjusted to be larger
than or equal to end. However, since the len is not set to zero. The
break-loop condition (ret && !len) will not meet. After it leaves the
while-loop, fallocate will return 1, which is an unexpected return
value.
We're not able to construct a reproducible way to let
btrfs_drop_extents() fail with -ENOSPC after it drops the last non-hole
file extent but with remaining holes left. However, it's quite easy to
fix. We just need to update and check the len every time before we call
find_first_non_hole(). To make the while loop more readable, we also
pull the variable updates to the bottom of loop like this:
while (cur_offset < end) {
...
// update cur_offset & len
// advance cur_offset & len in hole-punching case if needed
}
Reported-by: Robbie Ko <[email protected]>
Fixes: d77815461f04 ("btrfs: Avoid trucating page or punching hole in a
already existed hole.")
Reviewed-by: Robbie Ko <[email protected]>
Reviewed-by: Chung-Chiang Cheng <[email protected]>
Signed-off-by: BingJing Chang <[email protected]>
---
fs/btrfs/file.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 0e155f0..dccb017 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -2735,8 +2735,6 @@ int btrfs_replace_file_extents(struct inode *inode, struct btrfs_path *path,
extent_info->file_offset += replace_len;
}
- cur_offset = drop_args.drop_end;
-
ret = btrfs_update_inode(trans, root, BTRFS_I(inode));
if (ret)
break;
@@ -2756,7 +2754,9 @@ int btrfs_replace_file_extents(struct inode *inode, struct btrfs_path *path,
BUG_ON(ret); /* shouldn't happen */
trans->block_rsv = rsv;
- if (!extent_info) {
+ cur_offset = drop_args.drop_end;
+ len = end - cur_offset;
+ if (!extent_info && len) {
ret = find_first_non_hole(BTRFS_I(inode), &cur_offset,
&len);
if (unlikely(ret < 0))
--
2.7.4
On Thu, Mar 25, 2021 at 3:42 AM bingjingc <[email protected]> wrote:
>
> From: BingJing Chang <[email protected]>
>
> In commit d77815461f04 ("btrfs: Avoid trucating page or punching hole
> in a already existed hole."), existed holes can be skipped by calling
> find_first_non_hole() to adjust *start and *len. However, if the given
> len is invalid and large, when an EXTENT_MAP_HOLE extent is found, the
> *len will not be set to zero because (em->start + em->len) is less than
> (*start + *len). Then the ret will be 1 but the *len will not be set to
> 0. The propagated non-zero ret will result in fallocate failure.
>
> In the while-loop of btrfs_replace_file_extents(), len is not updated
> every time before it calls find_first_non_hole(). That is, after
> btrfs_drop_extents() successfully drops the last non-hole file extent,
> it may fail with -ENOSPC when attempting to drop a file extent item
> representing a hole. The problem can happen. After it calls
> find_first_non_hole(), the cur_offset will be adjusted to be larger
> than or equal to end. However, since the len is not set to zero. The
> break-loop condition (ret && !len) will not meet. After it leaves the
> while-loop, fallocate will return 1, which is an unexpected return
> value.
>
> We're not able to construct a reproducible way to let
> btrfs_drop_extents() fail with -ENOSPC after it drops the last non-hole
> file extent but with remaining holes left. However, it's quite easy to
> fix. We just need to update and check the len every time before we call
> find_first_non_hole(). To make the while loop more readable, we also
> pull the variable updates to the bottom of loop like this:
> while (cur_offset < end) {
> ...
> // update cur_offset & len
> // advance cur_offset & len in hole-punching case if needed
> }
>
> Reported-by: Robbie Ko <[email protected]>
> Fixes: d77815461f04 ("btrfs: Avoid trucating page or punching hole in a
> already existed hole.")
> Reviewed-by: Robbie Ko <[email protected]>
> Reviewed-by: Chung-Chiang Cheng <[email protected]>
> Signed-off-by: BingJing Chang <[email protected]>
Reviewed-by: Filipe Manana <[email protected]>
Looks good, thanks.
> ---
> fs/btrfs/file.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> index 0e155f0..dccb017 100644
> --- a/fs/btrfs/file.c
> +++ b/fs/btrfs/file.c
> @@ -2735,8 +2735,6 @@ int btrfs_replace_file_extents(struct inode *inode, struct btrfs_path *path,
> extent_info->file_offset += replace_len;
> }
>
> - cur_offset = drop_args.drop_end;
> -
> ret = btrfs_update_inode(trans, root, BTRFS_I(inode));
> if (ret)
> break;
> @@ -2756,7 +2754,9 @@ int btrfs_replace_file_extents(struct inode *inode, struct btrfs_path *path,
> BUG_ON(ret); /* shouldn't happen */
> trans->block_rsv = rsv;
>
> - if (!extent_info) {
> + cur_offset = drop_args.drop_end;
> + len = end - cur_offset;
> + if (!extent_info && len) {
> ret = find_first_non_hole(BTRFS_I(inode), &cur_offset,
> &len);
> if (unlikely(ret < 0))
> --
> 2.7.4
>
--
Filipe David Manana,
“Whether you think you can, or you think you can't — you're right.”
On Thu, Mar 25, 2021 at 09:56:22AM +0800, bingjingc wrote:
> From: BingJing Chang <[email protected]>
>
> In commit d77815461f04 ("btrfs: Avoid trucating page or punching hole
> in a already existed hole."), existed holes can be skipped by calling
> find_first_non_hole() to adjust *start and *len. However, if the given
> len is invalid and large, when an EXTENT_MAP_HOLE extent is found, the
> *len will not be set to zero because (em->start + em->len) is less than
> (*start + *len). Then the ret will be 1 but the *len will not be set to
> 0. The propagated non-zero ret will result in fallocate failure.
>
> In the while-loop of btrfs_replace_file_extents(), len is not updated
> every time before it calls find_first_non_hole(). That is, after
> btrfs_drop_extents() successfully drops the last non-hole file extent,
> it may fail with -ENOSPC when attempting to drop a file extent item
> representing a hole. The problem can happen. After it calls
> find_first_non_hole(), the cur_offset will be adjusted to be larger
> than or equal to end. However, since the len is not set to zero. The
> break-loop condition (ret && !len) will not meet. After it leaves the
> while-loop, fallocate will return 1, which is an unexpected return
> value.
>
> We're not able to construct a reproducible way to let
> btrfs_drop_extents() fail with -ENOSPC after it drops the last non-hole
> file extent but with remaining holes left. However, it's quite easy to
> fix. We just need to update and check the len every time before we call
> find_first_non_hole(). To make the while loop more readable, we also
> pull the variable updates to the bottom of loop like this:
> while (cur_offset < end) {
> ...
> // update cur_offset & len
> // advance cur_offset & len in hole-punching case if needed
> }
>
> Reported-by: Robbie Ko <[email protected]>
> Fixes: d77815461f04 ("btrfs: Avoid trucating page or punching hole in a
> already existed hole.")
> Reviewed-by: Robbie Ko <[email protected]>
> Reviewed-by: Chung-Chiang Cheng <[email protected]>
> Signed-off-by: BingJing Chang <[email protected]>
Thanks, added to misc-next.