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Date:   Thu, 1 Oct 2020 15:21:48 -0700
From:   "Darrick J. Wong" <>
To:     "Theodore Ts'o" <>,
        linux-ext4 <>
Subject: [PATCH] ext4: limit entries returned when counting fsmap records

From: Darrick J. Wong <>

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 <>
 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)
 		if (rec_fsblk > info->gfi_next_fsblk)

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