Re: [PATCH v9 05/14] fs: validate atomic writes after O_APPEND and limits

[sashiko-bot@kernel.org]

> An RWF_ATOMIC write on XFS with reflink can expose stale disk contents
> if O_APPEND or RLIMIT_FSIZE leaves it sector aligned but not block
> aligned.
> 
> XFS and ext4 call generic_atomic_write_valid() on the range that the
> caller passed. But generic_write_checks() changes the range later:
> O_APPEND moves the position, and RLIMIT_FSIZE cuts the length. XFS can
> then fill only a part of a new block, and still map the whole block into
> the file:
> 
>     block size 4096, i_size 512, O_APPEND
>     validated:        0 to 4095
>     written:          512 to 4607
>     new blocks:       0 to 8191
>     stale below EOF:  0 to 511
> 
> The fix used here is to validate an atomic write in
> generic_write_checks(), after its range is final, and to refuse one that
> was cut. XFS no longer picks the path of an atomic write by the
> alignment of the range that the caller passed.
> 
> Fixes: f096207d3276 ("xfs: Validate atomic writes")
> Fixes: 43c696f9d094 ("ext4: Check for atomic writes support in write iter")
> Signed-off-by: Chris Mason <mason@kernel.org>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261112214604.67875-1-mason@kernel.org?part=5