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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> 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 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: D598040018 X-Stat-Signature: nkcj9dtbyx6xxk1itkw4yhcq7zzn11f8 X-Rspam-User: X-HE-Tag: 1716171377-982698 X-HE-Meta: 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 IlZxlGPZ 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000115, 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. 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]; -- 2.34.1