Commit 88a5f8ce authored by Jan Kara's avatar Jan Kara Committed by Yongjian Sun
Browse files

ext4: don't set SB_RDONLY after filesystem errors 

mainline inclusion
from mainline-v6.12-rc1
commit d3476f3dad4ad68ae5f6b008ea6591d1520da5d8
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/IB2YWS
CVE: CVE-2024-50191

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d3476f3dad4ad68ae5f6b008ea6591d1520da5d8

--------------------------------

When the filesystem is mounted with errors=remount-ro, we were setting
SB_RDONLY flag to stop all filesystem modifications. We knew this misses
proper locking (sb->s_umount) and does not go through proper filesystem
remount procedure but it has been the way this worked since early ext2
days and it was good enough for catastrophic situation damage
mitigation. Recently, syzbot has found a way (see link) to trigger
warnings in filesystem freezing because the code got confused by
SB_RDONLY changing under its hands. Since these days we set
EXT4_FLAGS_SHUTDOWN on the superblock which is enough to stop all
filesystem modifications, modifying SB_RDONLY shouldn't be needed. So
stop doing that.

Link: https://lore.kernel.org/all/000000000000b90a8e061e21d12f@google.com


Reported-by: default avatarChristian Brauner <brauner@kernel.org>
Signed-off-by: default avatarJan Kara <jack@suse.cz>
Reviewed-by: default avatarChristian Brauner <brauner@kernel.org>
Link: https://patch.msgid.link/20240805201241.27286-1-jack@suse.cz


Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
Conflicts:
	fs/ext4/super.c
[Context differences.]
Signed-off-by: default avatarYongjian Sun <sunyongjian1@huawei.com>
parent 8a039651

fs/ext4/super.c

+5 −4
Original line number Diff line number Diff line
@@ -821,11 +821,12 @@ static void ext4_handle_error(struct super_block *sb, bool force_ro, int error, 


	ext4_msg(sb, KERN_CRIT, "Remounting filesystem read-only");

	/*

	 * Make sure updated value of ->s_mount_flags will be visible before

	 * ->s_flags update

	 * EXT4_FLAGS_SHUTDOWN was set which stops all filesystem

	 * modifications. We don't set SB_RDONLY because that requires

	 * sb->s_umount semaphore and setting it without proper remount

	 * procedure is confusing code such as freeze_super() leading to

	 * deadlocks and other problems.

	 */

	smp_wmb();

	sb->s_flags |= SB_RDONLY;

#ifdef CONFIG_EXT4_ERROR_REPORT

out:

	ext4_netlink_send_info(sb, force_ro ? 2 : 1);