linux-ext4 - [PATCH v2] resize2fs: resize2fs disk hardlinks will be error

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Message-ID: <9dcadf7a-b12a-c977-2de2-222e20f0cebe@huawei.com>
Date:   Tue, 4 Jan 2022 22:23:52 +0800
From:   zhanchengbin <zhanchengbin1@...wei.com>
To:     Theodore Ts'o <tytso@....edu>
CC:     <linux-ext4@...r.kernel.org>, <liuzhiqiang26@...wei.com>,
        <linux-ext4@...r.kernel.org>
Subject: [PATCH v2] resize2fs: resize2fs disk hardlinks will be error

Resize2fs disk hardlinks which mounting after the same name as tmpfs
  filesystem it will be error. The items in /proc/mounts are traversed,
when you get to tmpfs,file!=mnt->mnt_fsname, therefore, the
stat(mnt->mnt_fsname, &st_buf) branch is used, however, the values of
  file_rdev and st_buf.st_rdev are the same. As a result, the system
mistakenly considers that disk is mounted to /root/tmp. As a result
, resize2fs fails.

example:
dev_name="/dev/sdc" (ps: a disk in you self)
mkdir /root/tmp
mkdir /root/mnt
mkfs.ext4 -F -b 1024 -E "resize=10000000" "${dev_name}" 32768
mount -t tmpfs "${dev_name}" /root/tmp
mount "${dev_name}" /root/mnt
ln "${dev_name}" "${dev_name}"-ln
resize2fs "${dev_name}"-ln 6G

Signed-off-by: zhanchengbin <zhanchengbin1@...wei.com>
Signed-off-by: Zhiqiang Liu <liuzhiqiang26@...wei.com>

---
  lib/ext2fs/ismounted.c | 9 +++++++--
  1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/lib/ext2fs/ismounted.c b/lib/ext2fs/ismounted.c
index aee7d726..463a82a6 100644
--- a/lib/ext2fs/ismounted.c
+++ b/lib/ext2fs/ismounted.c
@@ -98,6 +98,7 @@ static errcode_t check_mntent_file(const char 
*mtab_file, const char *file,
  {
  	struct mntent 	*mnt;
  	struct stat	st_buf;
+	struct stat	dir_st_buf;
  	errcode_t	retval = 0;
  	dev_t		file_dev=0, file_rdev=0;
  	ino_t		file_ino=0;
@@ -144,8 +145,12 @@ static errcode_t check_mntent_file(const char 
*mtab_file, const char *file,
  		if (stat(mnt->mnt_fsname, &st_buf) == 0) {
  			if (ext2fsP_is_disk_device(st_buf.st_mode)) {
  #ifndef __GNU__
-				if (file_rdev && (file_rdev == st_buf.st_rdev))
-					break;
+				if (file_rdev && (file_rdev == st_buf.st_rdev)) {
+					if (stat(mnt->mnt_dir, &dir_st_buf) != 0)
+						continue;
+					if (file_rdev == dir_st_buf.st_dev)
+						break;
+				}
  				if (check_loop_mounted(mnt->mnt_fsname,
  						st_buf.st_rdev, file_dev,
  						file_ino) == 1)
-- 
2.27.0