From: Jan Kara jack@suse.cz

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/?i...

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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: Christian Brauner brauner@kernel.org Signed-off-by: Jan Kara jack@suse.cz Reviewed-by: Christian Brauner brauner@kernel.org Link: https://patch.msgid.link/20240805201241.27286-1-jack@suse.cz Signed-off-by: Theodore Ts'o tytso@mit.edu Conflicts: fs/ext4/super.c [Context differences.] Signed-off-by: Yongjian Sun sunyongjian1@huawei.com --- fs/ext4/super.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c index 4b81f9ae3454..367fa50be4d6 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -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);