2020-10-01 22:22:58

by Darrick J. Wong

Subject: [PATCH] ext4: limit entries returned when counting fsmap records

From: Darrick J. Wong <[email protected]>

If userspace asked fsmap to try to count the number of entries, we cannot
return more than UINT_MAX entries because fmh_entries is u32.
Therefore, stop counting if we hit this limit or else we will waste time
to return truncated results.

Fixes: 0c9ec4beecac ("ext4: support GETFSMAP ioctls")
Signed-off-by: Darrick J. Wong <[email protected]>
---
fs/ext4/fsmap.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/fs/ext4/fsmap.c b/fs/ext4/fsmap.c
index dbccf46f1770..37347ba868b7 100644
--- a/fs/ext4/fsmap.c
+++ b/fs/ext4/fsmap.c
@@ -108,6 +108,9 @@ static int ext4_getfsmap_helper(struct super_block *sb,

/* Are we just counting mappings? */
if (info->gfi_head->fmh_count == 0) {
+ if (info->gfi_head->fmh_entries == UINT_MAX)
+ return EXT4_QUERY_RANGE_ABORT;
+
if (rec_fsblk > info->gfi_next_fsblk)
info->gfi_head->fmh_entries++;

2020-10-03 05:28:10

by Theodore Ts'o

Subject: Re: [PATCH] ext4: limit entries returned when counting fsmap records

On Thu, Oct 01, 2020 at 03:21:48PM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <[email protected]>
>
> If userspace asked fsmap to try to count the number of entries, we cannot
> return more than UINT_MAX entries because fmh_entries is u32.
> Therefore, stop counting if we hit this limit or else we will waste time
> to return truncated results.
>
> Fixes: 0c9ec4beecac ("ext4: support GETFSMAP ioctls")
> Signed-off-by: Darrick J. Wong <[email protected]>

Applied, thanks.

- Ted