linux-ext4 - [PATCH 1/8] libext2fs: fix off-by-one bug in punch_extent

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Message-ID: <175182662987.1984706.5292286424808159532.stgit@frogsfrogsfrogs>
Date: Sun, 06 Jul 2025 11:31:00 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: tytso@....edu
Cc: linux-ext4@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: [PATCH 1/8] libext2fs: fix off-by-one bug in punch_extent_blocks

From: Darrick J. Wong <djwong@...nel.org>

punch_extent_blocks tries to validate its input parameters to make sure
that the physical range of blocks being punched do not go past the end
of the filesystem.  Unfortunately, there's an off-by-one bug in the
valiation, because start==0 count==10 is a perfectly valid range on a
10-block filesystem.

Cc: <linux-ext4@...r.kernel.org> # v1.46.6
Fixes: 6772d4969e9c90 ("libext2fs: check for invalid blocks in ext2fs_punch_blocks()")
Signed-off-by: "Darrick J. Wong" <djwong@...nel.org>
---
 lib/ext2fs/punch.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/ext2fs/punch.c b/lib/ext2fs/punch.c
index 80c699eb0c13f5..19b6a37824c589 100644
--- a/lib/ext2fs/punch.c
+++ b/lib/ext2fs/punch.c
@@ -201,7 +201,7 @@ static errcode_t punch_extent_blocks(ext2_filsys fs, ext2_ino_t ino,
 	errcode_t	retval = 0;

 	if (free_start < fs->super->s_first_data_block ||
-	    (free_start + free_count) >= ext2fs_blocks_count(fs->super))
+	    (free_start + free_count) > ext2fs_blocks_count(fs->super))
 		return EXT2_ET_BAD_BLOCK_NUM;

 	/* No bigalloc?  Just free each block. */