6.6-stable review patch. If anyone has any objections, please let me know.
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From: Kees Cook keescook@chromium.org
[ Upstream commit 0e108725f6cc5b3be9e607f89c9fbcbb236367b7 ]
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 exceeds source size 60 [-Werror=stringop-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 is adjusted to use dest length, which is what the original code did.
Reported-by: Arnd Bergmann arnd@arndb.de Fixes: dfbafa70bde2 ("string: Introduce strtomem() and strtomem_pad()") Tested-by: Arnd Bergmann arnd@arndb.de Cc: Andy Shevchenko andy@kernel.org Cc: linux-hardening@vger.kernel.org Signed-off-by: Kees Cook keescook@chromium.org Signed-off-by: Sasha Levin sashal@kernel.org --- 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 dbfc66400050f..9e3cb6923b0ef 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, const void *src, size_t count, */ #define strtomem_pad(dest, src, pad) do { \ const size_t _dest_len = __builtin_object_size(dest, 1); \ + const size_t _src_len = __builtin_object_size(src, 1); \ \ BUILD_BUG_ON(!__builtin_constant_p(_dest_len) || \ _dest_len == (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)
/** @@ -298,10 +300,11 @@ void memcpy_and_pad(void *dest, size_t dest_len, const void *src, size_t count, */ #define strtomem(dest, src) do { \ const size_t _dest_len = __builtin_object_size(dest, 1); \ + const size_t _src_len = __builtin_object_size(src, 1); \ \ BUILD_BUG_ON(!__builtin_constant_p(_dest_len) || \ _dest_len == (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)
/**