lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Tue, 18 Oct 2022 01:32:51 -0700 From: Kees Cook <keescook@...omium.org> To: linux-hardening@...r.kernel.org Cc: Kees Cook <keescook@...omium.org>, Nick Desaulniers <ndesaulniers@...gle.com>, llvm@...ts.linux.dev, linux-kernel@...r.kernel.org Subject: [PATCH] fortify: Short-circuit known-safe calls to strscpy() Replacing compile-time safe calls of strcpy()-related functions with strscpy() was always calling the full strscpy() logic when a builtin would be better. For example: char buf[16]; strcpy(buf, "yes"); would reduce to __builtin_memcpy(buf, "yes", 4), but not if it was: strscpy(buf, yes, sizeof(buf)); Fix this by checking if all sizes are known at compile-time. Cc: linux-hardening@...r.kernel.org Signed-off-by: Kees Cook <keescook@...omium.org> --- include/linux/fortify-string.h | 10 ++++++++++ lib/strscpy_kunit.c | 13 +++++++++++++ 2 files changed, 23 insertions(+) diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h index aa1a50009632..c473adb55cf5 100644 --- a/include/linux/fortify-string.h +++ b/include/linux/fortify-string.h @@ -321,6 +321,16 @@ __FORTIFY_INLINE ssize_t strscpy(char * const POS p, const char * const POS q, s if (__compiletime_lessthan(p_size, size)) __write_overflow(); + /* Short-circuit for compile-time known-safe lengths. */ + if (__compiletime_lessthan(p_size, SIZE_MAX)) { + len = __compiletime_strlen(q); + + if (len < SIZE_MAX && __compiletime_lessthan(len, size)) { + __underlying_memcpy(p, q, len + 1); + return len; + } + } + /* * This call protects from read overflow, because len will default to q * length if it smaller than size. diff --git a/lib/strscpy_kunit.c b/lib/strscpy_kunit.c index 98523f828d3a..a6b6344354ed 100644 --- a/lib/strscpy_kunit.c +++ b/lib/strscpy_kunit.c @@ -81,6 +81,8 @@ static void tc(struct kunit *test, char *src, int count, int expected, static void strscpy_test(struct kunit *test) { + char dest[8]; + /* * tc() uses a destination buffer of size 6 and needs at * least 2 characters spare (one for null and one to check for @@ -111,6 +113,17 @@ static void strscpy_test(struct kunit *test) tc(test, "ab", 4, 2, 2, 1, 1); tc(test, "a", 4, 1, 1, 1, 2); tc(test, "", 4, 0, 0, 1, 3); + + /* Compile-time-known source strings. */ + KUNIT_EXPECT_EQ(test, strscpy(dest, "", ARRAY_SIZE(dest)), 0); + KUNIT_EXPECT_EQ(test, strscpy(dest, "", 3), 0); + KUNIT_EXPECT_EQ(test, strscpy(dest, "", 1), 0); + KUNIT_EXPECT_EQ(test, strscpy(dest, "", 0), -E2BIG); + KUNIT_EXPECT_EQ(test, strscpy(dest, "Fixed", ARRAY_SIZE(dest)), 5); + KUNIT_EXPECT_EQ(test, strscpy(dest, "Fixed", 3), -E2BIG); + KUNIT_EXPECT_EQ(test, strscpy(dest, "Fixed", 1), -E2BIG); + KUNIT_EXPECT_EQ(test, strscpy(dest, "Fixed", 0), -E2BIG); + KUNIT_EXPECT_EQ(test, strscpy(dest, "This is too long", ARRAY_SIZE(dest)), -E2BIG); } static struct kunit_case strscpy_test_cases[] = { -- 2.34.1
Powered by blists - more mailing lists