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Message-ID: <Zvp6L+oFnfASaoHl@t14s> Date: Mon, 30 Sep 2024 12:15:11 +0200 From: Jan Stancek <jstancek@...hat.com> To: Jan Kara <jack@...e.cz>, ltp@...ts.linux.it Cc: Ted Tso <tytso@....edu>, linux-ext4@...r.kernel.org, Christian Brauner <brauner@...nel.org>, linux-fsdevel@...r.kernel.org Subject: Re: [PATCH] ext4: don't set SB_RDONLY after filesystem errors On Mon, Aug 05, 2024 at 10:12:41PM +0200, Jan Kara wrote: >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@...nel.org> >Signed-off-by: Jan Kara <jack@...e.cz> >--- > fs/ext4/super.c | 9 +++++---- > 1 file changed, 5 insertions(+), 4 deletions(-) > >Note that this patch introduces fstests failure with generic/459 test because >it assumes that either freezing succeeds or 'ro' is among mount options. But >we fail the freeze with EFSCORRUPTED. This needs fixing in the test but at this >point I'm not sure how exactly. > >diff --git a/fs/ext4/super.c b/fs/ext4/super.c >index e72145c4ae5a..93c016b186c0 100644 >--- a/fs/ext4/super.c >+++ b/fs/ext4/super.c >@@ -735,11 +735,12 @@ 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; Hi, shouldn't the SB_RDONLY still be set (in __ext4_remount()) for the case when user triggers the abort with mount(.., "abort")? Because now we seem to always hit the condition that returns EROFS to user-space. I'm seeing LTP's fanotify22 failing for a about week (roughly since commit de5cb0dcb74c) on: fanotify22.c:59: TINFO: Mounting /dev/loop0 to /tmp/LTP_fanqgL299/test_mnt fstyp=ext4 flags=21 fanotify22.c:59: TBROK: mount(/dev/loop0, test_mnt, ext4, 33, 0x4211ed) failed: EROFS (30) static void trigger_fs_abort(void) { SAFE_MOUNT(tst_device->dev, MOUNT_PATH, tst_device->fs_type, MS_REMOUNT|MS_RDONLY, "abort"); } Thanks, Jan
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