linux-ext4 - [PATCH] resize2fs: open device read-only when -P is passed

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Date:   Thu, 26 May 2022 13:08:28 +1200
From:   Michael Hudson-Doyle <michael.hudson@...ntu.com>
To:     linux-ext4@...r.kernel.org
Cc:     Michael Hudson-Doyle <michael.hudson@...ntu.com>
Subject: [PATCH] resize2fs: open device read-only when -P is passed

We ran into this because we noticed that resize2fs -P $device was
triggering udev events.

I added a very simple test that just checks resize2fs -P on a file
lacking the w bit succeeds.

Signed-off-by: Michael Hudson-Doyle <michael.hudson@...ntu.com>
---
 resize/main.c             | 8 ++++++--
 tests/scripts/resize_test | 8 ++++++++
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/resize/main.c b/resize/main.c
index bceaa1677..073c0bc7c 100644
--- a/resize/main.c
+++ b/resize/main.c
@@ -256,6 +256,7 @@ int main (int argc, char ** argv)
 	int		force_min_size = 0;
 	int		print_min_size = 0;
 	int		fd, ret;
+	int		open_flags = O_RDWR;
 	blk64_t		new_size = 0;
 	blk64_t		max_size = 0;
 	blk64_t		min_size = 0;
@@ -363,7 +364,10 @@ int main (int argc, char ** argv)
 		len = 2 * len;
 	}
 
-	fd = ext2fs_open_file(device_name, O_RDWR, 0);
+	if (print_min_size)
+		open_flags = O_RDONLY;
+
+	fd = ext2fs_open_file(device_name, open_flags, 0);
 	if (fd < 0) {
 		com_err("open", errno, _("while opening %s"),
 			device_name);
@@ -401,7 +405,7 @@ int main (int argc, char ** argv)
 #endif
 		io_ptr = unix_io_manager;
 
-	if (!(mount_flags & EXT2_MF_MOUNTED))
+	if (!(mount_flags & EXT2_MF_MOUNTED) && !print_min_size)
 		io_flags = EXT2_FLAG_RW | EXT2_FLAG_EXCLUSIVE;
 
 	io_flags |= EXT2_FLAG_64BITS | EXT2_FLAG_THREADS;
diff --git a/tests/scripts/resize_test b/tests/scripts/resize_test
index fc9d1c246..a000c85e5 100755
--- a/tests/scripts/resize_test
+++ b/tests/scripts/resize_test
@@ -60,6 +60,14 @@ rm -f $OUT_TMP
 echo $FSCK -fy $TMPFILE >> $LOG 2>&1 
 $FSCK -fy $TMPFILE >> $LOG 2>&1 
 
+chmod u-w $TMPFILE
+echo $RESIZE2FS -P $TMPFILE >> $LOG 2>&1
+if ! $RESIZE2FS -P $TMPFILE >> $LOG 2>&1
+then
+	return 1
+fi
+chmod u+w $TMPFILE
+
 echo $RESIZE2FS $RESIZE2FS_OPTS -d $DBG_FLAGS $TMPFILE $SIZE_2 >> $LOG 2>&1
 if ! $RESIZE2FS $RESIZE2FS_OPTS -d $DBG_FLAGS $TMPFILE $SIZE_2 >> $LOG 2>&1
 then
-- 
2.34.1