[PATCH 12/28] fortify: Convert strlcat() to snprintf() in strcat()

The fortified implementation of strcat() in include/linux/fortify-string.h
currently relies on strlcat() to perform bounded concatenation and detect
buffer overflows.

In preparation for removing the deprecated strlcat() API[1], replace the
strlcat() call in strcat(). When the destination buffer size is unknown
(SIZE_MAX), call __underlying_strcat() directly. Otherwise, determine the
destination length with __fortify_strlen() and append the source string
using __builtin_snprintf(), preserving the existing fortify_panic() check
on overflow.

Link: https://github.com/KSPP/linux/issues/370 [1]
Cc: codemender-patching+linux@google.com
Assisted-by: SecurityEngineer:Gemini1.5Pro [editor_update_file, shell_command_run, test_runner_run_kunit_test]
Signed-off-by: Bill Wendling <morbo@google.com>
---
Cc: Russell King <linux@armlinux.org.uk>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: WANG Xuerui <kernel@xen0n.name>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Cc: Helge Deller <deller@gmx.de>
Cc: Thomas Gleixner <tglx@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: x86@kernel.org
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Cc: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@gmail.com>
Cc: Simona Vetter <simona@ffwll.ch>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: "Thomas Hellström" <thomas.hellstrom@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Matthias Schwarzott <zzam@gentoo.org>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Tony Nguyen <anthony.l.nguyen@intel.com>
Cc: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Cc: Andrew Lunn <andrew+netdev@lunn.ch>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Arend van Spriel <arend.vanspriel@broadcom.com>
Cc: Rob Herring <robh@kernel.org>
Cc: Saravana Kannan <saravanak@kernel.org>
Cc: Krzysztof Kozlowski <krzk@kernel.org>
Cc: Sylwester Nawrocki <s.nawrocki@samsung.com>
Cc: Peter Griffin <peter.griffin@linaro.org>
Cc: Alim Akhtar <alim.akhtar@samsung.com>
Cc: Linus Walleij <linusw@kernel.org>
Cc: Anil Gurumurthy <anil.gurumurthy@qlogic.com>
Cc: Sudarsana Kalluru <sudarsana.kalluru@qlogic.com>
Cc: "Martin K. Petersen" <mkp@kernel.org>
Cc: Trond Myklebust <trondmy@kernel.org>
Cc: Anna Schumaker <anna@kernel.org>
Cc: Mike Marshall <hubcap@omnibond.com>
Cc: Martin Brandenburg <martin@omnibond.com>
Cc: Kees Cook <kees@kernel.org>
Cc: Jiri Pirko <jiri@resnulli.us>
Cc: Simon Horman <horms@kernel.org>
Cc: Chuck Lever <cel@kernel.org>
Cc: Jeff Layton <jlayton@kernel.org>
Cc: NeilBrown <neil@brown.name>
Cc: Olga Kornievskaia <okorniev@redhat.com>
Cc: Dai Ngo <Dai.Ngo@oracle.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Jaroslav Kysela <perex@perex.cz>
Cc: Takashi Iwai <tiwai@suse.com>
Cc: Bill Wendling <morbo@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
Cc: Kanglong Wang <redacted>
Cc: Tiezhu Yang <yangtiezhu@loongson.cn>
Cc: Qiang Ma <redacted>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Pengpeng Hou <redacted>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Breno Leitao <leitao@debian.org>
Cc: Thorsten Blum <blum@kernel.org>
Cc: Harshit Mogalapalli <redacted>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Lyude Paul <lyude@redhat.com>
Cc: Ashutosh Desai <redacted>
Cc: Imre Deak <redacted>
Cc: Dmitry Baryshkov <redacted>
Cc: Johan Hovold <johan@kernel.org>
Cc: Johannes Berg <redacted>
Cc: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Cc: Alexander Stein <redacted>
Cc: Cryolitia PukNgae <cryolitia@uniontech.com>
Cc: Jiaming Zhang <redacted>
Cc: Will Porter <redacted>
Cc: Cen Zhang <redacted>
Cc: "Cássio Gabriel" <redacted>
Cc: Rong Zhang <redacted>
Cc: Arun Raghavan <redacted>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Cc: loongarch@lists.linux.dev
Cc: linux-mips@vger.kernel.org
Cc: linux-parisc@vger.kernel.org
Cc: linux-edac@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Cc: intel-xe@lists.freedesktop.org
Cc: linux-input@vger.kernel.org
Cc: linux-media@vger.kernel.org
Cc: intel-wired-lan@lists.osuosl.org
Cc: netdev@vger.kernel.org
Cc: linux-wireless@vger.kernel.org
Cc: brcm80211@lists.linux.dev
Cc: brcm80211-dev-list.pdl@broadcom.com
Cc: devicetree@vger.kernel.org
Cc: linux-samsung-soc@vger.kernel.org
Cc: linux-gpio@vger.kernel.org
Cc: linux-scsi@vger.kernel.org
Cc: linux-nfs@vger.kernel.org
Cc: devel@lists.orangefs.org
Cc: linux-hardening@vger.kernel.org
Cc: linux-sound@vger.kernel.org
---
 include/linux/fortify-string.h | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h
index cf841dc71fef..0b489124bfcb 100644
--- a/include/linux/fortify-string.h
+++ b/include/linux/fortify-string.h

@@ -363,7 +363,12 @@ __FORTIFY_INLINE __diagnose_as(__builtin_strcat, 1, 2)
 char *strcat(char * const POS p, const char *q)
 {
 	const size_t p_size = __member_size(p);
-	const size_t wanted = strlcat(p, q, p_size);
+
+	if (p_size == SIZE_MAX)
+		return __underlying_strcat(p, q);
+
+	const size_t p_len = __fortify_strlen(p);
+	const size_t wanted = p_len + __builtin_snprintf(p + p_len, p_size - p_len, "%s", q);
 
 	if (p_size <= wanted)
 		fortify_panic(FORTIFY_FUNC_strcat, FORTIFY_WRITE, p_size, wanted + 1, p);

-- 
2.55.0.1032.g73a4cd73de-goog