On Thu, 15 Jun 2023 13:38:48 +0200, Jan Kara wrote: > The reconfigure / remount code takes a lot of effort to protect > filesystem's reconfiguration code from racing writes on remounting > read-only. However during remounting read-only filesystem to read-write > mode userspace writes can start immediately once we clear SB_RDONLY > flag. This is inconvenient for example for ext4 because we need to do > some writes to the filesystem (such as preparation of quota files) > before we can take userspace writes so we are clearing SB_RDONLY flag > before we are fully ready to accept userpace writes and syzbot has found > a way to exploit this [1]. Also as far as I'm reading the code > the filesystem remount code was protected from racing writes in the > legacy mount path by the mount's MNT_READONLY flag so this is relatively > new problem. It is actually fairly easy to protect remount read-write > from racing writes using sb->s_readonly_remount flag so let's just do > that instead of having to workaround these races in the filesystem code. > > [...] Applied to the vfs.misc branch of the vfs/vfs.git tree. Patches in the vfs.misc branch should appear in linux-next soon. Please report any outstanding bugs that were missed during review in a new review to the original patch series allowing us to drop it. It's encouraged to provide Acked-bys and Reviewed-bys even though the patch has now been applied. If possible patch trailers will be updated. tree: https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git branch: vfs.misc [1/1] fs: Protect reconfiguration of sb read-write from racing writes https://git.kernel.org/vfs/vfs/c/496de0b41695
