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[198.0.35.241]) by smtp.gmail.com with ESMTPSA id x26-20020aa79ada000000b0069309cbc220sm3625673pfp.121.2023.10.18.11.07.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Oct 2023 11:07:21 -0700 (PDT) From: Kees Cook To: Andy Shevchenko Cc: Kees Cook , Arnd Bergmann , linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] string: Adjust strtomem_pad() logic to allow for smaller sources Date: Wed, 18 Oct 2023 11:07:17 -0700 Message-Id: <20231018180709.work.293-kees@kernel.org> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=2772; i=keescook@chromium.org; h=from:subject:message-id; bh=Rt1eV6YjyZR8hPzO/9qK3HhySIUW19g/DhKIx9uJ9jQ=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBlMB7VZWKyUdda+qSVCCbnpliyQcdpJPLHtjhC6 wQ+xa1Q9k2JAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCZTAe1QAKCRCJcvTf3G3A JvLtD/4vR8iWSvia1DQYbZ8m+tqzhImzUGpErsH/KDBTULSjLG+5iWaI1Sk4C2zSlqEzo7SqEXM Kt3AZDESIQynRLJky5h+GNObiXryvBdfesyvC1ycPKr5Aror8ouzxAFzwgl6IRtNFLsn5z/9+VX 5chlFTq8xtubHLh3BXGvqQvKjRAdzDVBCGx9x5g/7rLJGaBD3rhJj6eYMsJpvwmFDc6EEyG8HKD YxeBhJLkHBSnkMpFRVYspLGVmsEa+lvAOHwfQa15huGvb4AtnJsoS85L0hXWbzNfjp5aDB1TzzL +38CUoVhtBzuAnEyXBWadZV06HbXyl6M3PEFE7kF+w47SGFXJ85SCN9Gm44sTyZDDxiUsLoiWjy 6jeKdH4O6pGyXuXlEnpEEBsIzmxzVF9Rl74P5e7vC7Eli1Jz7ILMVEpbrINStNOOkUBizb7oalu ZEIQrRlZWjm0Q+iD1y5oFExoM0edBPWIgBsi0qnWyQdnSFJk+2iySCuSaQczSAvorCWOukEZlRy iF3WFmv3J2WdEgXos+iuNxMbZalvvBAHYgdQleYGEoG2pdBz73lTvz3/bH2+Y4B/WTgvUwVjLre ljV/6yoBVamHn6dHWUj1x6AFevYMlr897FIZ07lhgqZpRDCBzmMjPvQNMCEC8mRyTvmsO0EiXNq HaRyCCV cae/bc5Q== X-Developer-Key: i=keescook@chromium.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Arnd noticed we have a case where a shorter source string is being copied into a destination byte array, but this results in a strnlen() call that exceeds the size of the source. This is seen with -Wstringop-overread: In file included from ../include/linux/uuid.h:11, from ../include/linux/mod_devicetable.h:14, from ../include/linux/cpufeature.h:12, from ../arch/x86/coco/tdx/tdx.c:7: ../arch/x86/coco/tdx/tdx.c: In function 'tdx_panic.constprop': ../include/linux/string.h:284:9: error: 'strnlen' specified bound 64 exceed= s source size 60 [-Werror=3Dstringop-overread] 284 | memcpy_and_pad(dest, _dest_len, src, strnlen(src, _dest_len= ), pad); \ | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~= ~~~~~~~ ../arch/x86/coco/tdx/tdx.c:124:9: note: in expansion of macro 'strtomem_pad' 124 | strtomem_pad(message.str, msg, '\0'); | ^~~~~~~~~~~~ Use the smaller of the two buffer sizes when calling strnlen(). When src length is unknown (SIZE_MAX), it will use dest length, which is what the original code did. Reported-by: Arnd Bergmann Fixes: dfbafa70bde2 ("string: Introduce strtomem() and strtomem_pad()") Cc: Andy Shevchenko Cc: linux-hardening@vger.kernel.org Signed-off-by: Kees Cook Tested-by: Arnd Bergmann --- include/linux/string.h | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/include/linux/string.h b/include/linux/string.h index dbfc66400050..9e3cb6923b0e 100644 --- a/include/linux/string.h +++ b/include/linux/string.h @@ -277,10 +277,12 @@ void memcpy_and_pad(void *dest, size_t dest_len, cons= t void *src, size_t count, */ #define strtomem_pad(dest, src, pad) do { \ const size_t _dest_len =3D __builtin_object_size(dest, 1); \ + const size_t _src_len =3D __builtin_object_size(src, 1); \ \ BUILD_BUG_ON(!__builtin_constant_p(_dest_len) || \ _dest_len =3D=3D (size_t)-1); \ - memcpy_and_pad(dest, _dest_len, src, strnlen(src, _dest_len), pad); \ + memcpy_and_pad(dest, _dest_len, src, \ + strnlen(src, min(_src_len, _dest_len)), pad); \ } while (0) =20 /** @@ -298,10 +300,11 @@ void memcpy_and_pad(void *dest, size_t dest_len, cons= t void *src, size_t count, */ #define strtomem(dest, src) do { \ const size_t _dest_len =3D __builtin_object_size(dest, 1); \ + const size_t _src_len =3D __builtin_object_size(src, 1); \ \ BUILD_BUG_ON(!__builtin_constant_p(_dest_len) || \ _dest_len =3D=3D (size_t)-1); \ - memcpy(dest, src, min(_dest_len, strnlen(src, _dest_len))); \ + memcpy(dest, src, strnlen(src, min(_src_len, _dest_len))); \ } while (0) =20 /** --=20 2.34.1