From patchwork Mon Jun 25 17:49:23 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Florian Weimer X-Patchwork-Id: 28026 Received: (qmail 93364 invoked by alias); 25 Jun 2018 17:49:39 -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 93146 invoked by uid 89); 25 Jun 2018 17:49:27 -0000 Authentication-Results: sourceware.org; auth=none X-Spam-SWARE-Status: No, score=-25.9 required=5.0 tests=BAYES_00, GIT_PATCH_0, GIT_PATCH_1, GIT_PATCH_2, GIT_PATCH_3, KAM_LAZY_DOMAIN_SECURITY, SPF_HELO_PASS autolearn=ham version=3.3.2 spammy=Increase, retry X-HELO: mx1.redhat.com Date: Mon, 25 Jun 2018 19:49:23 +0200 To: libc-alpha@sourceware.org Subject: [PATCH] getgrent_next_nss (compat-initgroups): Remove alloca fallback [BZ #18023] User-Agent: Heirloom mailx 12.5 7/5/10 MIME-Version: 1.0 Message-Id: <20180625174923.5E6A643994575@oldenburg.str.redhat.com> From: fweimer@redhat.com (Florian Weimer) If the caller-supplied buffer is not large enough, fall back directly malloc. The previous __libc_use_alloca check was incorrect because it did not take into account that extend_alloca may fail to merge allocations, so it would underestimate the stack space being used by roughly a factor of two. 2018-06-25 Florian Weimer [BZ #18023] * nss/nss_compat/compat-initgroups.c (getgrent_next_nss): Fall back to malloc directly, without stack allocations. diff --git a/nss/nss_compat/compat-initgroups.c b/nss/nss_compat/compat-initgroups.c index 74414f4622..540eee863c 100644 --- a/nss/nss_compat/compat-initgroups.c +++ b/nss/nss_compat/compat-initgroups.c @@ -261,7 +261,6 @@ getgrent_next_nss (ent_t *ent, char *buffer, size_t buflen, const char *user, overwrite the pointer with one to a bigger buffer. */ char *tmpbuf = buffer; size_t tmplen = buflen; - bool use_malloc = false; for (int i = 0; i < mystart; i++) { @@ -270,29 +269,26 @@ getgrent_next_nss (ent_t *ent, char *buffer, size_t buflen, const char *user, == NSS_STATUS_TRYAGAIN && *errnop == ERANGE) { - if (__libc_use_alloca (tmplen * 2)) - { - if (tmpbuf == buffer) - { - tmplen *= 2; - tmpbuf = __alloca (tmplen); - } - else - tmpbuf = extend_alloca (tmpbuf, tmplen, tmplen * 2); - } - else - { - tmplen *= 2; - char *newbuf = realloc (use_malloc ? tmpbuf : NULL, tmplen); - - if (newbuf == NULL) - { - status = NSS_STATUS_TRYAGAIN; - goto done; - } - use_malloc = true; - tmpbuf = newbuf; - } + /* Check for overflow. */ + if (__glibc_unlikely (tmplen * 2 < tmplen)) + { + __set_errno (ENOMEM); + status = NSS_STATUS_TRYAGAIN; + goto done; + } + /* Increase the size. Make sure that we retry + with a reasonable size. */ + tmplen *= 2; + if (tmplen < 1024) + tmplen = 1024; + if (tmpbuf != buffer) + free (tmpbuf); + tmpbuf = malloc (tmplen); + if (__glibc_unlikely (tmpbuf == NULL)) + { + status = NSS_STATUS_TRYAGAIN; + goto done; + } } if (__builtin_expect (status != NSS_STATUS_NOTFOUND, 1)) @@ -320,7 +316,7 @@ getgrent_next_nss (ent_t *ent, char *buffer, size_t buflen, const char *user, status = NSS_STATUS_NOTFOUND; done: - if (use_malloc) + if (tmpbuf != buffer) free (tmpbuf); }