Re: [PATCH v2 27/34] efivarfs: stop using SB_RDONLY for read-only efivar ops

[sashiko-bot@kernel.org]

> Since commit 94f7f6182c72 ("efivarfs: automatically update super block
> flag") efivarfs_ops_notifier() sets or clears SB_RDONLY whenever the
> efivar ops switch between ops that can and ops that can't set variables,
> e.g. when tee_stmm_efi is probed or removed. It does that at any time
> without holding s_umount. efivarfs is frozen on every suspend and if the
> ops switch while it's frozen thaw_super() either leaves the s_writers
> rwsems locked or releases rwsems nobody holds.
> 
> So keep the state in efivarfs. The notifier sets and clears a new
> EFIVARFS_OPS_RDONLY flag instead and efivarfs_fill_super() initializes
> it under efivar_lock() so a switch can't slip in. fill_super doesn't set
> SB_RDONLY either. systemd mounts efivarfs before tee_stmm_efi is loaded
> and the mount has to become writable then. create, unlink, setattr,
> fileattr_set, write and opening for write fail with EROFS while the flag
> is set. Like the SB_RDONLY check this runs without efivars_lock so a
> write racing with a switch can still call a NULL ->set_variable. That's
> not new.
> 
> efivarfs_reconfigure() only refuses a remount from read-only to
> read-write while the flag is set and returns EROFS. It used to refuse
> every remount without "ro" which would break option-only remounts.
> 
> With read-only ops efivarfs is mounted "rw" now. statfs() doesn't report
> ST_RDONLY anymore and access(W_OK) succeeds.
> 
> Fixes: 94f7f6182c72 ("efivarfs: automatically update super block flag")
> Cc: stable@vger.kernel.org
> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261029-work-fs-sb_rdonly-v2-0-2f44f64f0b66@kernel.org?part=27