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[34.168.202.30]) by smtp.gmail.com with ESMTPSA id s13-20020a65690d000000b00477fb27eaddsm3074241pgq.63.2022.12.01.17.35.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 01 Dec 2022 17:35:51 -0800 (PST) From: jeffxu@chromium.org To: skhan@linuxfoundation.org, keescook@chromium.org Cc: akpm@linux-foundation.org, dmitry.torokhov@gmail.com, dverkamp@chromium.org, hughd@google.com, jeffxu@google.com, jorgelo@chromium.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, mnissler@chromium.org, jannh@google.com, linux-hardening@vger.kernel.org, Jeff Xu Subject: [PATCH v3] selftests/memfd: add tests for F_SEAL_EXEC Date: Fri, 2 Dec 2022 01:34:01 +0000 Message-Id: <20221202013404.163143-4-jeffxu@google.com> X-Mailer: git-send-email 2.39.0.rc0.267.gcb52ba06e7-goog In-Reply-To: <20221202013404.163143-1-jeffxu@google.com> References: <20221202013404.163143-1-jeffxu@google.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-hardening@vger.kernel.org From: Daniel Verkamp Basic tests to ensure that user/group/other execute bits cannot be changed after applying F_SEAL_EXEC to a memfd. Co-developed-by: Jeff Xu Signed-off-by: Jeff Xu Signed-off-by: Daniel Verkamp --- tools/testing/selftests/memfd/memfd_test.c | 129 ++++++++++++++++++++- 1 file changed, 128 insertions(+), 1 deletion(-) diff --git a/tools/testing/selftests/memfd/memfd_test.c b/tools/testing/selftests/memfd/memfd_test.c index 94df2692e6e4..1d7e7b36bbdd 100644 --- a/tools/testing/selftests/memfd/memfd_test.c +++ b/tools/testing/selftests/memfd/memfd_test.c @@ -28,12 +28,44 @@ #define MFD_DEF_SIZE 8192 #define STACK_SIZE 65536 +#ifndef F_SEAL_EXEC +#define F_SEAL_EXEC 0x0020 +#endif + +#ifndef MAX_PATH +#define MAX_PATH 256 +#endif + /* * Default is not to test hugetlbfs */ static size_t mfd_def_size = MFD_DEF_SIZE; static const char *memfd_str = MEMFD_STR; +static ssize_t fd2name(int fd, char *buf, size_t bufsize) +{ + char buf1[MAX_PATH]; + int size; + ssize_t nbytes; + + size = snprintf(buf1, MAX_PATH, "/proc/self/fd/%d", fd); + if (size < 0) { + printf("snprintf(%d) failed on %m\n", fd); + abort(); + } + + /* + * reserver one byte for string termination. + */ + nbytes = readlink(buf1, buf, bufsize-1); + if (nbytes == -1) { + printf("readlink(%s) failed %m\n", buf1); + abort(); + } + buf[nbytes] = '\0'; + return nbytes; +} + static int mfd_assert_new(const char *name, loff_t sz, unsigned int flags) { int r, fd; @@ -98,11 +130,14 @@ static unsigned int mfd_assert_get_seals(int fd) static void mfd_assert_has_seals(int fd, unsigned int seals) { + char buf[MAX_PATH]; + int nbytes; unsigned int s; + fd2name(fd, buf, MAX_PATH); s = mfd_assert_get_seals(fd); if (s != seals) { - printf("%u != %u = GET_SEALS(%d)\n", seals, s, fd); + printf("%u != %u = GET_SEALS(%s)\n", seals, s, buf); abort(); } } @@ -594,6 +629,64 @@ static void mfd_fail_grow_write(int fd) } } +static void mfd_assert_mode(int fd, int mode) +{ + struct stat st; + char buf[MAX_PATH]; + int nbytes; + + fd2name(fd, buf, MAX_PATH); + + if (fstat(fd, &st) < 0) { + printf("fstat(%s) failed: %m\n", buf); + abort(); + } + + if ((st.st_mode & 07777) != mode) { + printf("fstat(%s) wrong file mode 0%04o, but expected 0%04o\n", + buf, (int)st.st_mode & 07777, mode); + abort(); + } +} + +static void mfd_assert_chmod(int fd, int mode) +{ + char buf[MAX_PATH]; + int nbytes; + + fd2name(fd, buf, MAX_PATH); + + if (fchmod(fd, mode) < 0) { + printf("fchmod(%s, 0%04o) failed: %m\n", buf, mode); + abort(); + } + + mfd_assert_mode(fd, mode); +} + +static void mfd_fail_chmod(int fd, int mode) +{ + struct stat st; + char buf[MAX_PATH]; + int nbytes; + + fd2name(fd, buf, MAX_PATH); + + if (fstat(fd, &st) < 0) { + printf("fstat(%s) failed: %m\n", buf); + abort(); + } + + if (fchmod(fd, mode) == 0) { + printf("fchmod(%s, 0%04o) didn't fail as expected\n", + buf, mode); + abort(); + } + + /* verify that file mode bits did not change */ + mfd_assert_mode(fd, st.st_mode & 07777); +} + static int idle_thread_fn(void *arg) { sigset_t set; @@ -880,6 +973,39 @@ static void test_seal_resize(void) close(fd); } +/* + * Test SEAL_EXEC + * Test that chmod() cannot change x bits after sealing + */ +static void test_seal_exec(void) +{ + int fd; + + printf("%s SEAL-EXEC\n", memfd_str); + + fd = mfd_assert_new("kern_memfd_seal_exec", + mfd_def_size, + MFD_CLOEXEC | MFD_ALLOW_SEALING); + + mfd_assert_mode(fd, 0777); + + mfd_assert_chmod(fd, 0644); + + mfd_assert_has_seals(fd, 0); + mfd_assert_add_seals(fd, F_SEAL_EXEC); + mfd_assert_has_seals(fd, F_SEAL_EXEC); + + mfd_assert_chmod(fd, 0600); + mfd_fail_chmod(fd, 0777); + mfd_fail_chmod(fd, 0670); + mfd_fail_chmod(fd, 0605); + mfd_fail_chmod(fd, 0700); + mfd_fail_chmod(fd, 0100); + mfd_assert_chmod(fd, 0666); + + close(fd); +} + /* * Test sharing via dup() * Test that seals are shared between dupped FDs and they're all equal. @@ -1059,6 +1185,7 @@ int main(int argc, char **argv) test_seal_shrink(); test_seal_grow(); test_seal_resize(); + test_seal_exec(); test_share_dup("SHARE-DUP", ""); test_share_mmap("SHARE-MMAP", "");