From: Alejandro Colomar <alx+linux-hardening@kernel.org>
To: Joe Perches <joe@perches.com>
Cc: Alejandro Colomar <alx@kernel.org>,
linux-hardening@vger.kernel.org,
Krzysztof Kozlowski <krzk@kernel.org>,
"Maciej W. Rozycki" <macro@orcam.me.uk>,
Geert Uytterhoeven <geert@linux-m68k.org>,
Andreas Schwab <schwab@linux-m68k.org>,
Andy Shevchenko <andy@kernel.org>,
Bartosz Golaszewski <brgl@kernel.org>,
Daniel Scally <djrscally@gmail.com>,
Danilo Krummrich <dakr@kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Hans Verkuil <hverkuil-cisco@xs4all.nl>,
Heikki Krogerus <heikki.krogerus@linux.intel.com>,
Johan Hovold <johan@kernel.org>, Kees Cook <kees@kernel.org>,
Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
Len Brown <lenb@kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Linus Walleij <linusw@kernel.org>,
Namhyung Kim <namhyung@kernel.org>,
"Rafael J. Wysocki" <rafael@kernel.org>,
Rob Herring <robh@kernel.org>,
Sakari Ailus <sakari.ailus@linux.intel.com>,
Saravana Kannan <saravanak@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
Tom Zanussi <zanussi@kernel.org>,
linux-acpi@vger.kernel.org, driver-core@lists.linux.dev,
linux-kernel@vger.kernel.org, devicetree@vger.kernel.org,
linux-gpio@vger.kernel.org,
Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Subject: Re: [PATCH v6 02/19] string: Add strprefix()
Date: Sat, 14 Nov 2026 18:03:36 +0100 [thread overview]
Message-ID: <aviTcYS995cB-lTY@devuan> (raw)
In-Reply-To: <6de04b9cf2dfe9ff1dacdddc0a76752a714a991c.camel@perches.com>
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Hi Joe,
> Date: 2026-11-14 07:28:23-0800
> From: Joe Perches <joe@perches.com>
>
> On Sat, 2026-11-14 at 16:22 +0100, Alejandro Colomar wrote:
> > As Bartosz reported, str_has_prefix() has a bug: it can't differentiate
> > between an empty prefix matching an empty string from a non-matching
> > prefix. This is a fundamental design flaw in this API, and not
> > something that can be fixed.
>
> I still think this description is poor.
> It's neither a bug nor a flaw.
> It's a design choice.
As explained in more detail in the subthread, I think it is a bug.
If the function name were strprefix_len(), it would be a legitimate
design choice, since 0 would indeed be the length of such a prefix, and
it would be arguably useful to return 0 on a non-matching prefix.
But the function is named str_has_prefix(). Since an empty string is by
convention (strstr(3), etc.) the prefix of every string, returning false
is a bug. Since the function returns 0 for such a case, it misbehaves.
Perhaps we can reach an agreement if I prepend this commit with one that
renames all uses of str_has_prefix() to strprefix_len(). Then, I would
agree to consider this as a design choice, and remove the text above.
Cheers,
Alex
--
<https://www.alejandro-colomar.es>
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next prev parent reply other threads:[~2026-11-14 17:03 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-14 15:21 [PATCH v6 00/19] Add strprefix() and fix a bug with it Alejandro Colomar
2026-11-14 15:21 ` [PATCH v6 01/19] string: Add streq() Alejandro Colomar
2026-11-14 15:22 ` [PATCH v6 02/19] string: Add strprefix() Alejandro Colomar
2026-11-14 15:28 ` Joe Perches
2026-11-14 17:03 ` Alejandro Colomar [this message]
2026-11-14 15:53 ` Joe Perches
2026-11-14 16:59 ` Alejandro Colomar
2026-11-14 15:22 ` [PATCH v6 03/19] string: Document corner-case misbehavior in str_has_prefix() for empty prefix Alejandro Colomar
2026-11-14 15:22 ` [PATCH v6 04/19] device property: Fix fwnode_name_eq() for empty node names Alejandro Colomar
2026-11-14 15:22 ` [PATCH v6 05/19] stddef: Add const_cast() Alejandro Colomar
2026-11-14 15:22 ` [PATCH v6 06/19] string: Add [C]QChar_of() and QVoid_of() Alejandro Colomar
2026-11-14 15:22 ` [PATCH v6 07/19] string: Make strprefix() const-qualifier-generic Alejandro Colomar
2026-11-14 15:22 ` [PATCH v6 08/19] perf map: Use bool for return type instead of int Alejandro Colomar
2026-11-14 15:22 ` [PATCH v6 09/19] string: Make strstarts() a legacy alias for strprefix() Alejandro Colomar
2026-11-14 15:33 ` sashiko-bot
2026-11-14 15:51 ` Alejandro Colomar
2026-11-14 15:23 ` [PATCH v6 10/19] platform/x86: hp-bioscfg: Rename local variable Alejandro Colomar
2026-11-14 16:04 ` Joe Perches
2026-11-14 17:08 ` Alejandro Colomar
2026-11-14 15:23 ` [PATCH v6 11/19] treewide: s/strstarts/strprefix/g Alejandro Colomar
2026-11-14 15:23 ` [PATCH v6 12/19] string: Remove strstarts() Alejandro Colomar
2026-11-14 15:29 ` sashiko-bot
2026-11-14 15:45 ` Alejandro Colomar
2026-11-14 15:23 ` [PATCH v6 13/19] s390/test_unwind: Use bool for booleans Alejandro Colomar
2026-11-14 15:23 ` [PATCH v6 14/19] treewide: Replace boolean uses of str_has_prefix() by strprefix() Alejandro Colomar
2026-11-14 15:23 ` [PATCH v6 15/19] treewide: Replace some " Alejandro Colomar
2026-11-14 15:34 ` sashiko-bot
2026-11-14 15:47 ` Alejandro Colomar
2026-11-14 15:23 ` [PATCH v6 16/19] string: Add strsuffix() Alejandro Colomar
2026-11-14 15:24 ` [PATCH v6 17/19] string: Make strends() a legacy alias for strsuffix() Alejandro Colomar
2026-11-14 15:24 ` [PATCH v6 18/19] treewide: s/\<strends\>/strsuffix/g Alejandro Colomar
2026-11-14 15:24 ` [PATCH v6 19/19] string: Remove strends() Alejandro Colomar
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