From patchwork Tue Mar 20 17:54:39 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Joseph Myers X-Patchwork-Id: 26391 Received: (qmail 39821 invoked by alias); 20 Mar 2018 17:54:47 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org Delivered-To: mailing list libc-alpha@sourceware.org Received: (qmail 39809 invoked by uid 89); 20 Mar 2018 17:54:46 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-24.5 required=5.0 tests=AWL, BAYES_00, GIT_PATCH_0, GIT_PATCH_1, GIT_PATCH_2, GIT_PATCH_3, RCVD_IN_DNSWL_NONE, SPF_PASS, URIBL_RED autolearn=ham version=3.3.2 spammy=Hx-languages-length:1863 X-HELO: relay1.mentorg.com Date: Tue, 20 Mar 2018 17:54:39 +0000 From: Joseph Myers To: Paul Eggert CC: Subject: Re: Fix signed integer overflow in random_r (bug 17343) In-Reply-To: Message-ID: References: User-Agent: Alpine 2.20 (DEB 67 2015-01-07) MIME-Version: 1.0 X-ClientProxiedBy: svr-ies-mbx-01.mgc.mentorg.com (139.181.222.1) To svr-ies-mbx-01.mgc.mentorg.com (139.181.222.1) On Fri, 16 Mar 2018, Paul Eggert wrote: > Joseph Myers wrote: > > int32_t val = state[0]; > > - val = ((state[0] * 1103515245) + 12345) & 0x7fffffff; > > + val = ((state[0] * 1103515245U) + 12345U) & 0x7fffffff; > > The first assignment to VAL (in the unchanged line) is unnecessary; I suggest > coalescing the two lines. Here's a version of the patch that includes that cleanup. Fix signed integer overflow in random_r (bug 17343). Bug 17343 reports that stdlib/random_r.c has code with undefined behavior because of signed integer overflow on int32_t. This patch changes the code so that the possibly overflowing computations use unsigned arithmetic instead. Note that the bug report refers to "Most code" in that file. The places changed in this patch are the only ones I found where I think such overflow can occur. Tested for x86_64 and x86. 2018-03-20 Joseph Myers [BZ #17343] * stdlib/random_r.c (__random_r): Use unsigned arithmetic for possibly overflowing computations. diff --git a/stdlib/random_r.c b/stdlib/random_r.c index 4d2f0d4..7342cd8 100644 --- a/stdlib/random_r.c +++ b/stdlib/random_r.c @@ -361,8 +361,7 @@ __random_r (struct random_data *buf, int32_t *result) if (buf->rand_type == TYPE_0) { - int32_t val = state[0]; - val = ((state[0] * 1103515245) + 12345) & 0x7fffffff; + int32_t val = ((state[0] * 1103515245U) + 12345U) & 0x7fffffff; state[0] = val; *result = val; } @@ -371,9 +370,9 @@ __random_r (struct random_data *buf, int32_t *result) int32_t *fptr = buf->fptr; int32_t *rptr = buf->rptr; int32_t *end_ptr = buf->end_ptr; - int32_t val; + uint32_t val; - val = *fptr += *rptr; + val = *fptr += (uint32_t) *rptr; /* Chucking least random bit. */ *result = (val >> 1) & 0x7fffffff; ++fptr;