Re: [PATCH v3 04/33] ecryptfs: fall back to a read-only lower file

[sashiko-bot@kernel.org]

> ecryptfs opens the lower file read-write unless the lower inode is
> IS_RDONLY(). A read-only mount underneath refuses that and so does ext4
> after an error since commit d3476f3dad4a ("ext4: don't set SB_RDONLY
> after filesystem errors"). Then every lookup of a regular file fails
> with EROFS. The other filesystems are about to behave like ext4, so fall
> back to opening the lower file read-only. Opening an ecryptfs file for
> writing then fails with EPERM like on top of a read-only superblock.
> 
> truncate(2) and creating a file still write to the lower file and
> would trip the WARN_ON_ONCE() in __kernel_write_iter(). So let
> ecryptfs_write_lower() and __ecryptfs_truncate() refuse that with EROFS.
> Opening an empty file doesn't try to write the header through a
> read-only lower file at all, read_or_initialize_metadata() skips it and
> the open fails with EIO.
> 
> Note that ecryptfs never takes write access on the lower mount. On a
> read-only bind mount that was only a problem for directories so far.
> With this regular files can be unlinked and changed through it too.
> 
> 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/20261113-work-fs-sb_rdonly-v3-0-0be92bb73709@kernel.org?part=4