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Fri, 21 Jun 2024 20:50:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1719003046; bh=HGKiztfmnXGwe57zj0+vTZfhNT7KQZ5JNN+BGrOb5Qw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=RAkDBFKVl8xmtb2DHIPOV2tWg9gbzOL1odQSCGDEXJNPgM0WUxIxBe87GtqqWJ+4A 1Ere96aP9tXLhWixhIZSvQheDU5VDOtlYZ7/DpmebD/f4Tp0apl4GBwQ0utpvwApMh KAeYFQUGf8tbr+xiQDD/fo3hDTyV18sQydUOi+eZsvrNA+K2MSdVQdGwKJLzt7ejma e3onkPPrABfNag37HD3ojtklzAwWmw5WQ/6vezXvCejKws996+3d20U3Ir7nxeBm4w kXP35UpmP8mmSxdjYJpGQhw+KveCa+Jz9gCAWSOsOHo7XrHNY/Nb/jhTL1PYPx5LyR LdVoE6OLcFbCg== From: Kees Cook To: Guenter Roeck Cc: Kees Cook , Eric Biederman , Justin Stitt , Alexander Viro , Christian Brauner , Jan Kara , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Alexey Dobriyan , Laurent Vivier , Lukas Bulwahn , linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: [PATCH v2 2/2] exec: Avoid pathological argc, envc, and bprm->p values Date: Fri, 21 Jun 2024 13:50:44 -0700 Message-Id: <20240621205046.4001362-2-kees@kernel.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240621204729.it.434-kees@kernel.org> References: <20240621204729.it.434-kees@kernel.org> MIME-Version: 1.0 X-Developer-Signature: v=1; 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a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 X-Stat-Signature: 11pd3x4yct4bwo4k6kj1bzm1t9rsx4si X-Rspamd-Queue-Id: D7F1E1C0011 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1719003047-224440 X-HE-Meta: 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 2y0QsXj+ 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Make sure nothing goes wrong with the string counters or the bprm's belief about the stack pointer. Add checks and matching self-tests. Take special care for !CONFIG_MMU, since argmin is not exposed there. For 32-bit validation, 32-bit UML was used: $ tools/testing/kunit/kunit.py run \ --make_options CROSS_COMPILE=i686-linux-gnu- \ --make_options SUBARCH=i386 \ exec For !MMU validation, m68k was used: $ tools/testing/kunit/kunit.py run \ --arch m68k --make_option CROSS_COMPILE=m68k-linux-gnu- \ exec Link: https://lore.kernel.org/r/20240520021615.741800-2-keescook@chromium.org Signed-off-by: Kees Cook --- Cc: Guenter Roeck 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 | 10 +++++++++- fs/exec_test.c | 28 +++++++++++++++++++++++++++- 2 files changed, 36 insertions(+), 2 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index b7bc63bfb907..5b580ff8d955 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -490,6 +490,9 @@ static inline int bprm_set_stack_limit(struct linux_binprm *bprm, unsigned long limit) { #ifdef CONFIG_MMU + /* Avoid a pathological bprm->p. */ + if (bprm->p < limit) + return -E2BIG; bprm->argmin = bprm->p - limit; #endif return 0; @@ -531,6 +534,9 @@ 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 @@ -544,7 +550,9 @@ 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; diff --git a/fs/exec_test.c b/fs/exec_test.c index 8fea0bf0b7f5..7c77d039680b 100644 --- a/fs/exec_test.c +++ b/fs/exec_test.c @@ -8,9 +8,34 @@ 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 }, +#ifdef CONFIG_MMU + /* 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 }, +#endif /* * 0 rlim_stack will get raised to ARG_MAX. With 1 string pointer, * we should see p - ARG_MAX + sizeof(void *). @@ -88,6 +113,7 @@ 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];