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Thu, 07 Apr 2022 13:00:33 -0700 (PDT) Received: from [192.168.1.128] ([71.205.29.0]) by smtp.gmail.com with ESMTPSA id u15-20020a056e021a4f00b002c665afb993sm12217063ilv.11.2022.04.07.13.00.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 07 Apr 2022 13:00:33 -0700 (PDT) Subject: Re: [PATCH 3/4] selftests/memfd: add tests for F_SEAL_EXEC To: Daniel Verkamp , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Andrew Morton , Hugh Dickins , Mattias Nissler , Dmitry Torokhov , Kees Cook , Shuah Khan References: <20220401220834.307660-1-dverkamp@chromium.org> <20220401220834.307660-4-dverkamp@chromium.org> From: Shuah Khan Message-ID: <6f71a4f3-8f8e-926b-883c-1df630cfc1a0@linuxfoundation.org> Date: Thu, 7 Apr 2022 14:00:32 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <20220401220834.307660-4-dverkamp@chromium.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 4/1/22 4:08 PM, Daniel Verkamp wrote: > Basic tests to ensure that user/group/other execute bits cannot be > changed after applying F_SEAL_EXEC to a memfd. > > Signed-off-by: Daniel Verkamp > --- > tools/testing/selftests/memfd/memfd_test.c | 80 ++++++++++++++++++++++ > 1 file changed, 80 insertions(+) > > diff --git a/tools/testing/selftests/memfd/memfd_test.c b/tools/testing/selftests/memfd/memfd_test.c > index 94df2692e6e4..fdb0e46e9df9 100644 > --- a/tools/testing/selftests/memfd/memfd_test.c > +++ b/tools/testing/selftests/memfd/memfd_test.c > @@ -28,6 +28,10 @@ > #define MFD_DEF_SIZE 8192 > #define STACK_SIZE 65536 > > +#ifndef F_SEAL_EXEC > +#define F_SEAL_EXEC 0x0020 > +#endif > + > /* > * Default is not to test hugetlbfs > */ > @@ -594,6 +598,48 @@ static void mfd_fail_grow_write(int fd) > } > } > > +static void mfd_assert_mode(int fd, int mode) > +{ > + struct stat st; > + > + if (fstat(fd, &st) < 0) { > + printf("fstat(%d) failed: %m\n", fd); Let's print the filename here - just printing fd isn't useful. > + abort(); > + } else if ((st.st_mode & 07777) != mode) { > + printf("wrong file mode 0%04o, but expected 0%04o\n", > + (int)st.st_mode & 07777, mode); This one doesn't even print fd - same comment here about filename. > + abort(); > + } > +} > + > +static void mfd_assert_chmod(int fd, int mode) > +{ > + if (fchmod(fd, mode) < 0) { > + printf("fchmod(0%04o) failed: %m\n", mode); Same here. > + abort(); > + } > + > + mfd_assert_mode(fd, mode); > +} > + > +static void mfd_fail_chmod(int fd, int mode) > +{ > + struct stat st; > + > + if (fstat(fd, &st) < 0) { > + printf("fstat(%d) failed: %m\n", fd); Same comment about filename > + abort(); > + } > + > + if (fchmod(fd, mode) == 0) { > + printf("fchmod(0%04o) didn't fail as expected\n"); Same comment about filename > + 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 +926,39 @@ 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 +1138,7 @@ 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", ""); > The rest looks good. thanks, -- Shuah