Re: [f2fs-dev] [PATCH 1/3] libfs: reject casefolded names that fold to ".", "..", or empty

[sashiko-bot@kernel.org]

> Unicode normalization and casefolding (utf8_casefold()) strips code
> points with the Default_Ignorable_Code_Point property, such as U+202E
> (RIGHT-TO-LEFT OVERRIDE) or U+200B (ZERO WIDTH SPACE). As a result:
> 
> 1. A filename consisting of "." or ".." followed by ignorable characters
>    (e.g. ".\xe2\x80\xae" or "..\xe2\x80\xae") bypasses VFS special-entry
>    handling during path walk, but casefolds to "." or "..".
> 2. A filename consisting solely of ignorable characters (e.g.
>    "\xe2\x80\xae") casefolds to the empty string "" (length 0), causing
>    any two distinct ignorable-only filenames to compare and hash as
>    equal.
> 
> Update generic_ci_d_hash(), generic_ci_d_compare(), generic_ci_match(),
> and generic_ci_validate_strict_name() to reject case-insensitive
> hashing, matching, and creation of filenames that casefold to "", ".",
> or "..", while preserving exact byte-equality matches (such as NFS
> export lookups of literal ".."). Using a 3-byte stack buffer with
> utf8_casefold() detects all three cases in O(1) space without heap
> allocations.
> 
> Fixes: c843843e714c ("fs: Add standard casefolding support")
> Co-developed-by: Dmitry Torokhov <dtor@google.com>
> Signed-off-by: Dmitry Torokhov <dtor@google.com>
> Signed-off-by: Sarthak Kukreti <sarthakkukreti@google.com>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261113065332.929085-1-sarthakkukreti@google.com?part=1