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a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 Since bprm_stack_limits() operates with very limited side-effects, add it as the first exec.c KUnit test. Add to Kconfig and adjust MAINTAINERS file to include it. Tested on 64-bit UML: $ tools/testing/kunit/kunit.py run exec Signed-off-by: Kees Cook --- Cc: Eric Biederman Cc: Justin Stitt Cc: Alexander Viro Cc: Christian Brauner Cc: Jan Kara Cc: linux-fsdevel@vger.kernel.org Cc: linux-mm@kvack.org --- MAINTAINERS | 2 + fs/Kconfig.binfmt | 8 ++++ fs/exec.c | 13 ++++++ fs/exec_test.c | 113 ++++++++++++++++++++++++++++++++++++++++++++++ 4 files changed, 136 insertions(+) create mode 100644 fs/exec_test.c diff --git a/MAINTAINERS b/MAINTAINERS index 7c121493f43d..845165dbb756 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -8039,7 +8039,9 @@ S: Supported T: git git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git for-next/execve F: Documentation/userspace-api/ELF.rst F: fs/*binfmt_*.c +F: fs/Kconfig.binfmt F: fs/exec.c +F: fs/exec_test.c F: include/linux/binfmts.h F: include/linux/elf.h F: include/uapi/linux/binfmts.h diff --git a/fs/Kconfig.binfmt b/fs/Kconfig.binfmt index f5693164ca9a..58657f2d9719 100644 --- a/fs/Kconfig.binfmt +++ b/fs/Kconfig.binfmt @@ -176,4 +176,12 @@ config COREDUMP certainly want to say Y here. Not necessary on systems that never need debugging or only ever run flawless code. +config EXEC_KUNIT_TEST + bool "Build execve tests" if !KUNIT_ALL_TESTS + depends on KUNIT + default KUNIT_ALL_TESTS + help + This builds the exec KUnit tests, which tests boundary conditions + of various aspects of the exec internals. + endmenu diff --git a/fs/exec.c b/fs/exec.c index b3c40fbb325f..1d45e1a2d620 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -475,6 +475,15 @@ static int count_strings_kernel(const char *const *argv) return i; } +/* + * Calculate bprm->argmin from: + * - _STK_LIM + * - ARG_MAX + * - bprm->rlim_stack.rlim_cur + * - bprm->argc + * - bprm->envc + * - bprm->p + */ static int bprm_stack_limits(struct linux_binprm *bprm) { unsigned long limit, ptr_size; @@ -2200,3 +2209,7 @@ static int __init init_fs_exec_sysctls(void) fs_initcall(init_fs_exec_sysctls); #endif /* CONFIG_SYSCTL */ + +#ifdef CONFIG_EXEC_KUNIT_TEST +#include "exec_test.c" +#endif diff --git a/fs/exec_test.c b/fs/exec_test.c new file mode 100644 index 000000000000..32a90c6f47e7 --- /dev/null +++ b/fs/exec_test.c @@ -0,0 +1,113 @@ +// SPDX-License-Identifier: GPL-2.0-only +#include + +struct bprm_stack_limits_result { + struct linux_binprm bprm; + int expected_rc; + unsigned long expected_argmin; +}; + +static const struct bprm_stack_limits_result bprm_stack_limits_results[] = { + /* Giant values produce -E2BIG */ + { { .p = ULONG_MAX, .rlim_stack.rlim_cur = ULONG_MAX, + .argc = INT_MAX, .envc = INT_MAX }, .expected_rc = -E2BIG }, + /* + * 0 rlim_stack will get raised to ARG_MAX. With 1 string pointer, + * we should see p - ARG_MAX + sizeof(void *). + */ + { { .p = ULONG_MAX, .rlim_stack.rlim_cur = 0, + .argc = 1, .envc = 0 }, .expected_argmin = ULONG_MAX - ARG_MAX + sizeof(void *)}, + /* Validate that argc is always raised to a minimum of 1. */ + { { .p = ULONG_MAX, .rlim_stack.rlim_cur = 0, + .argc = 0, .envc = 0 }, .expected_argmin = ULONG_MAX - ARG_MAX + sizeof(void *)}, + /* + * 0 rlim_stack will get raised to ARG_MAX. With pointers filling ARG_MAX, + * we should see -E2BIG. (Note argc is always raised to at least 1.) + */ + { { .p = ULONG_MAX, .rlim_stack.rlim_cur = 0, + .argc = ARG_MAX / sizeof(void *), .envc = 0 }, .expected_rc = -E2BIG }, + { { .p = ULONG_MAX, .rlim_stack.rlim_cur = 0, + .argc = 0, .envc = ARG_MAX / sizeof(void *) - 1 }, .expected_rc = -E2BIG }, + { { .p = ULONG_MAX, .rlim_stack.rlim_cur = 0, + .argc = ARG_MAX / sizeof(void *) + 1, .envc = 0 }, .expected_rc = -E2BIG }, + { { .p = ULONG_MAX, .rlim_stack.rlim_cur = 0, + .argc = 0, .envc = ARG_MAX / sizeof(void *) }, .expected_rc = -E2BIG }, + /* And with one less, we see space for exactly 1 pointer. */ + { { .p = ULONG_MAX, .rlim_stack.rlim_cur = 0, + .argc = (ARG_MAX / sizeof(void *)) - 1, .envc = 0 }, + .expected_argmin = ULONG_MAX - sizeof(void *) }, + { { .p = ULONG_MAX, .rlim_stack.rlim_cur = 0, + .argc = 0, .envc = (ARG_MAX / sizeof(void *)) - 2, }, + .expected_argmin = ULONG_MAX - sizeof(void *) }, + /* If we raise rlim_stack / 4 to exactly ARG_MAX, nothing changes. */ + { { .p = ULONG_MAX, .rlim_stack.rlim_cur = ARG_MAX * 4, + .argc = ARG_MAX / sizeof(void *), .envc = 0 }, .expected_rc = -E2BIG }, + { { .p = ULONG_MAX, .rlim_stack.rlim_cur = ARG_MAX * 4, + .argc = 0, .envc = ARG_MAX / sizeof(void *) - 1 }, .expected_rc = -E2BIG }, + { { .p = ULONG_MAX, .rlim_stack.rlim_cur = ARG_MAX * 4, + .argc = ARG_MAX / sizeof(void *) + 1, .envc = 0 }, .expected_rc = -E2BIG }, + { { .p = ULONG_MAX, .rlim_stack.rlim_cur = ARG_MAX * 4, + .argc = 0, .envc = ARG_MAX / sizeof(void *) }, .expected_rc = -E2BIG }, + { { .p = ULONG_MAX, .rlim_stack.rlim_cur = ARG_MAX * 4, + .argc = (ARG_MAX / sizeof(void *)) - 1, .envc = 0 }, + .expected_argmin = ULONG_MAX - sizeof(void *) }, + { { .p = ULONG_MAX, .rlim_stack.rlim_cur = ARG_MAX * 4, + .argc = 0, .envc = (ARG_MAX / sizeof(void *)) - 2, }, + .expected_argmin = ULONG_MAX - sizeof(void *) }, + /* But raising it another pointer * 4 will provide space for 1 more pointer. */ + { { .p = ULONG_MAX, .rlim_stack.rlim_cur = (ARG_MAX + sizeof(void *)) * 4, + .argc = ARG_MAX / sizeof(void *), .envc = 0 }, + .expected_argmin = ULONG_MAX - sizeof(void *) }, + { { .p = ULONG_MAX, .rlim_stack.rlim_cur = (ARG_MAX + sizeof(void *)) * 4, + .argc = 0, .envc = ARG_MAX / sizeof(void *) - 1 }, + .expected_argmin = ULONG_MAX - sizeof(void *) }, + /* Raising rlim_stack / 4 to _STK_LIM / 4 * 3 will see more space. */ + { { .p = ULONG_MAX, .rlim_stack.rlim_cur = 4 * (_STK_LIM / 4 * 3), + .argc = 0, .envc = 0 }, + .expected_argmin = ULONG_MAX - (_STK_LIM / 4 * 3) + sizeof(void *) }, + { { .p = ULONG_MAX, .rlim_stack.rlim_cur = 4 * (_STK_LIM / 4 * 3), + .argc = 0, .envc = 0 }, + .expected_argmin = ULONG_MAX - (_STK_LIM / 4 * 3) + sizeof(void *) }, + /* But raising it any further will see no increase. */ + { { .p = ULONG_MAX, .rlim_stack.rlim_cur = 4 * (_STK_LIM / 4 * 3 + sizeof(void *)), + .argc = 0, .envc = 0 }, + .expected_argmin = ULONG_MAX - (_STK_LIM / 4 * 3) + sizeof(void *) }, + { { .p = ULONG_MAX, .rlim_stack.rlim_cur = 4 * (_STK_LIM / 4 * + sizeof(void *)), + .argc = 0, .envc = 0 }, + .expected_argmin = ULONG_MAX - (_STK_LIM / 4 * 3) + sizeof(void *) }, + { { .p = ULONG_MAX, .rlim_stack.rlim_cur = 4 * _STK_LIM, + .argc = 0, .envc = 0 }, + .expected_argmin = ULONG_MAX - (_STK_LIM / 4 * 3) + sizeof(void *) }, + { { .p = ULONG_MAX, .rlim_stack.rlim_cur = 4 * _STK_LIM, + .argc = 0, .envc = 0 }, + .expected_argmin = ULONG_MAX - (_STK_LIM / 4 * 3) + sizeof(void *) }, +}; + +static void exec_test_bprm_stack_limits(struct kunit *test) +{ + /* Double-check the constants. */ + KUNIT_EXPECT_EQ(test, _STK_LIM, SZ_8M); + KUNIT_EXPECT_EQ(test, ARG_MAX, 32 * SZ_4K); + + for (int i = 0; i < ARRAY_SIZE(bprm_stack_limits_results); i++) { + const struct bprm_stack_limits_result *result = &bprm_stack_limits_results[i]; + struct linux_binprm bprm = result->bprm; + int rc; + + rc = bprm_stack_limits(&bprm); + KUNIT_EXPECT_EQ_MSG(test, rc, result->expected_rc, "on loop %d", i); + KUNIT_EXPECT_EQ_MSG(test, bprm.argmin, result->expected_argmin, "on loop %d", i); + } +} + +static struct kunit_case exec_test_cases[] = { + KUNIT_CASE(exec_test_bprm_stack_limits), + {}, +}; + +static struct kunit_suite exec_test_suite = { + .name = "exec", + .test_cases = exec_test_cases, +}; + +kunit_test_suite(exec_test_suite); From patchwork Mon May 20 02:16:12 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kees Cook X-Patchwork-Id: 13668011 Received: from mail-oo1-f41.google.com (mail-oo1-f41.google.com [209.85.161.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B84351847 for ; 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Sun, 19 May 2024 19:16:16 -0700 (PDT) Received: from www.outflux.net ([198.0.35.241]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-6f4d2ae0d88sm18130632b3a.122.2024.05.19.19.16.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 19 May 2024 19:16:16 -0700 (PDT) From: Kees Cook To: Eric Biederman Cc: Kees Cook , Justin Stitt , Alexander Viro , Christian Brauner , Jan Kara , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: [PATCH 2/2] exec: Avoid pathological argc, envc, and bprm->p values Date: Sun, 19 May 2024 19:16:12 -0700 Message-Id: <20240520021615.741800-2-keescook@chromium.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240520021337.work.198-kees@kernel.org> References: <20240520021337.work.198-kees@kernel.org> Precedence: bulk X-Mailing-List: linux-hardening@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=4282; i=keescook@chromium.org; h=from:subject; bh=m0sCs3UZgNNm707rXtEZ6kEPFezkWis9xLUpPwvfVyU=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBmSrJsc9KHOfxr0Wciwne6IO1ZYX00AOmo6RSzn ssGypyJUcmJAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCZkqybAAKCRCJcvTf3G3A JsKKD/9uBa8Jg3Y7sh77JlX02ZEuM20xIOhSZRe/yX+ttzgjv6KsJ9e3EIzgOYyNTIetZdFOmUb t7Mw60rDwAc5bbFe12eX/hkmt1YSB65lOeZh46s0Pvb0yVyjdgvu7JNmVJav2jDq97QQfVjpbQL 8Lyv6j+6foBWoBRnIwTVPXKlVz1By4gwEVfkh7B1vHQyDU1T0uC3LJ3cI4TtM0Q5kf/OdNrG7Go dkULpZMKwZJXiLDtJxOWAzncvtbcHJpMh2a+kEde/uu48+ASF8pQYWAa7uHHnhmF5ic5z6+Sp0u H+c2g3O+CnK7HKpNC6/kPNQktzYH0YHsn6SZTovtLwkgHJctXZMNx+6u+0i+9HT4konRiJttZUf tJXAxAljiX1a9z2NcyqjkRymJmABRN+tnuT7PU4QwPrzcrzMWPNRQyo9Tkt6Wcnyqyv/OcGcuZI Qx+xQCDv+Pmjn5D3ccDOTJ3Xmp5ZmZzVCw3CJBAM05GyVuKO0dm6b9i/hATOiP8oNQztwOHg671 NES0OBKauNxcL9Ob7iGOT8Jtc+gZkkrdNw/8K6IGViwNkZY9lzH5Lt14+HgRT8jpKdmC5GlEdDL YhbDjJZJ0aJNroXppjbZpDpNNuiHqPewUDpRlFh5orwTPevgk8c9hGJXEn1xDtG/0cpcx1Vesj6 xd0fVBCgpYbeRWQ== X-Developer-Key: i=keescook@chromium.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 Make sure nothing goes wrong with the string counters or the bprm's belief about the stack pointer. Add checks and matching self-tests. For 32-bit validation, this was run under 32-bit UML: $ tools/testing/kunit/kunit.py run --make_options SUBARCH=i386 exec Signed-off-by: Kees Cook --- Cc: Eric Biederman Cc: Justin Stitt Cc: Alexander Viro Cc: Christian Brauner Cc: Jan Kara Cc: linux-fsdevel@vger.kernel.org Cc: linux-mm@kvack.org --- fs/exec.c | 11 ++++++++++- fs/exec_test.c | 26 +++++++++++++++++++++++++- 2 files changed, 35 insertions(+), 2 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index 1d45e1a2d620..5dcdd115739e 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -503,6 +503,9 @@ static int bprm_stack_limits(struct linux_binprm *bprm) * of argument strings even with small stacks */ limit = max_t(unsigned long, limit, ARG_MAX); + /* Reject totally pathological counts. */ + if (bprm->argc < 0 || bprm->envc < 0) + return -E2BIG; /* * We must account for the size of all the argv and envp pointers to * the argv and envp strings, since they will also take up space in @@ -516,11 +519,17 @@ static int bprm_stack_limits(struct linux_binprm *bprm) * argc can never be 0, to keep them from walking envp by accident. * See do_execveat_common(). */ - ptr_size = (max(bprm->argc, 1) + bprm->envc) * sizeof(void *); + if (check_add_overflow(max(bprm->argc, 1), bprm->envc, &ptr_size) || + check_mul_overflow(ptr_size, sizeof(void *), &ptr_size)) + return -E2BIG; if (limit <= ptr_size) return -E2BIG; limit -= ptr_size; + /* Avoid a pathological bprm->p. */ + if (bprm->p < limit) + return -E2BIG; + bprm->argmin = bprm->p - limit; return 0; } diff --git a/fs/exec_test.c b/fs/exec_test.c index 32a90c6f47e7..f2d4a80c861d 100644 --- a/fs/exec_test.c +++ b/fs/exec_test.c @@ -8,9 +8,32 @@ struct bprm_stack_limits_result { }; static const struct bprm_stack_limits_result bprm_stack_limits_results[] = { - /* Giant values produce -E2BIG */ + /* Negative argc/envc counts produce -E2BIG */ + { { .p = ULONG_MAX, .rlim_stack.rlim_cur = ULONG_MAX, + .argc = INT_MIN, .envc = INT_MIN }, .expected_rc = -E2BIG }, + { { .p = ULONG_MAX, .rlim_stack.rlim_cur = ULONG_MAX, + .argc = 5, .envc = -1 }, .expected_rc = -E2BIG }, + { { .p = ULONG_MAX, .rlim_stack.rlim_cur = ULONG_MAX, + .argc = -1, .envc = 10 }, .expected_rc = -E2BIG }, + /* The max value of argc or envc is MAX_ARG_STRINGS. */ { { .p = ULONG_MAX, .rlim_stack.rlim_cur = ULONG_MAX, .argc = INT_MAX, .envc = INT_MAX }, .expected_rc = -E2BIG }, + { { .p = ULONG_MAX, .rlim_stack.rlim_cur = ULONG_MAX, + .argc = MAX_ARG_STRINGS, .envc = MAX_ARG_STRINGS }, .expected_rc = -E2BIG }, + { { .p = ULONG_MAX, .rlim_stack.rlim_cur = ULONG_MAX, + .argc = 0, .envc = MAX_ARG_STRINGS }, .expected_rc = -E2BIG }, + { { .p = ULONG_MAX, .rlim_stack.rlim_cur = ULONG_MAX, + .argc = MAX_ARG_STRINGS, .envc = 0 }, .expected_rc = -E2BIG }, + /* + * On 32-bit system these argc and envc counts, while likely impossible + * to represent within the associated TASK_SIZE, could overflow the + * limit calculation, and bypass the ptr_size <= limit check. + */ + { { .p = ULONG_MAX, .rlim_stack.rlim_cur = ULONG_MAX, + .argc = 0x20000001, .envc = 0x20000001 }, .expected_rc = -E2BIG }, + /* Make sure a pathological bprm->p doesn't cause an overflow. */ + { { .p = sizeof(void *), .rlim_stack.rlim_cur = ULONG_MAX, + .argc = 10, .envc = 10 }, .expected_rc = -E2BIG }, /* * 0 rlim_stack will get raised to ARG_MAX. With 1 string pointer, * we should see p - ARG_MAX + sizeof(void *). @@ -88,6 +111,7 @@ static void exec_test_bprm_stack_limits(struct kunit *test) /* Double-check the constants. */ KUNIT_EXPECT_EQ(test, _STK_LIM, SZ_8M); KUNIT_EXPECT_EQ(test, ARG_MAX, 32 * SZ_4K); + KUNIT_EXPECT_EQ(test, MAX_ARG_STRINGS, 0x7FFFFFFF); for (int i = 0; i < ARRAY_SIZE(bprm_stack_limits_results); i++) { const struct bprm_stack_limits_result *result = &bprm_stack_limits_results[i];