From patchwork Tue Nov 13 20:54:34 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: DJ Delorie X-Patchwork-Id: 30137 Received: (qmail 23869 invoked by alias); 13 Nov 2018 20:54:40 -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 23852 invoked by uid 89); 13 Nov 2018 20:54:39 -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, KAM_SHORT, SPF_HELO_PASS autolearn=ham version=3.3.2 spammy=rec, effectively X-HELO: mx1.redhat.com From: DJ Delorie To: Florian Weimer Cc: libc-alpha@sourceware.org Subject: Re: [patch] tcache double free check In-Reply-To: <87k1ln72lk.fsf@oldenburg.str.redhat.com> (message from Florian Weimer on Thu, 08 Nov 2018 21:09:59 +0100) Date: Tue, 13 Nov 2018 15:54:34 -0500 Message-ID: MIME-Version: 1.0 I decided to move the double free test to just _int_free, but before the tcache_put call. The test was always called anyway; moving this means it's only coded in one place. I added a probe that triggers when the expensive scan happens, which effectively means "double free detected" (or a one in a zillion chance meaning "I wasted some cycles" ;) I'm still including the dlerror patch only to avoid regressions; I still don't know for sure if that patch is the correct one for that error. * malloc/malloc.c (tcache_entry): Add key field. (tcache_put): Set it. (tcache_get): Likewise. (_int_free): Check for double free in tcache. * malloc/tst-tcfree1.c: New. * malloc/tst-tcfree2.c: New. * malloc/Makefile: Run the new tests. * manual/probes.texi: Document memory_tcache_double_free probe. * dlfcn/dlerror.c (check_free): Prevent double frees. Reviewed-by: Carlos O'Donell diff --git a/dlfcn/dlerror.c b/dlfcn/dlerror.c index 33574faab6..96bf925333 100644 --- a/dlfcn/dlerror.c +++ b/dlfcn/dlerror.c @@ -198,7 +198,10 @@ check_free (struct dl_action_result *rec) Dl_info info; if (_dl_addr (check_free, &info, &map, NULL) != 0 && map->l_ns == 0) #endif - free ((char *) rec->errstring); + { + free ((char *) rec->errstring); + rec->errstring = NULL; + } } } diff --git a/malloc/Makefile b/malloc/Makefile index 7d54bad866..e6dfbfc14c 100644 --- a/malloc/Makefile +++ b/malloc/Makefile @@ -38,6 +38,7 @@ tests := mallocbug tst-malloc tst-valloc tst-calloc tst-obstack \ tst-malloc_info \ tst-malloc-too-large \ tst-malloc-stats`-cancellation \ + tst-tcfree1 tst-tcfree2 \ tests-static := \ tst-interpose-static-nothread \ diff --git a/malloc/malloc.c b/malloc/malloc.c index 67cdfd0ad2..0749d3fe70 100644 --- a/malloc/malloc.c +++ b/malloc/malloc.c @@ -2888,6 +2888,8 @@ mremap_chunk (mchunkptr p, size_t new_size) typedef struct tcache_entry { struct tcache_entry *next; + /* This field exists to detect double frees. */ + struct tcache_perthread_struct *key; } tcache_entry; /* There is one of these for each thread, which contains the @@ -2911,6 +2913,11 @@ tcache_put (mchunkptr chunk, size_t tc_idx) { tcache_entry *e = (tcache_entry *) chunk2mem (chunk); assert (tc_idx < TCACHE_MAX_BINS); + + /* Mark this chunk as "in the tcache" so the test in _int_free will + detect a double free. */ + e->key = tcache; + e->next = tcache->entries[tc_idx]; tcache->entries[tc_idx] = e; ++(tcache->counts[tc_idx]); @@ -2926,6 +2933,7 @@ tcache_get (size_t tc_idx) assert (tcache->entries[tc_idx] > 0); tcache->entries[tc_idx] = e->next; --(tcache->counts[tc_idx]); + e->key = NULL; return (void *) e; } @@ -4166,6 +4174,26 @@ _int_free (mstate av, mchunkptr p, int have_lock) { size_t tc_idx = csize2tidx (size); + /* Check to see if it's already in the tcache. */ + tcache_entry *e = (tcache_entry *) chunk2mem (p); + + /* This test succeeds on double free. However, we don't 100% + trust it (it also matches random payload data at a 1 in + 2^ chance), so verify it's not an unlikely coincidence + before aborting. */ + if (__glibc_unlikely (e->key == tcache && tcache)) + { + tcache_entry *tmp; + LIBC_PROBE (memory_tcache_double_free, 2, e, tc_idx); + for (tmp = tcache->entries[tc_idx]; + tmp; + tmp = tmp->next) + if (tmp == e) + malloc_printerr ("free(): double free detected in tcache 2"); + /* If we get here, it was a coincidence. We've wasted a few + cycles, but don't abort. */ + } + if (tcache && tc_idx < mp_.tcache_bins && tcache->counts[tc_idx] < mp_.tcache_count) diff --git a/malloc/tst-tcfree1.c b/malloc/tst-tcfree1.c new file mode 100644 index 0000000000..b1258f403f --- /dev/null +++ b/malloc/tst-tcfree1.c @@ -0,0 +1,40 @@ +/* Copyright (C) 2018 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + . */ + +#include +#include +#include +#include +#include +#include +#include + +static int +do_test (void) +{ + char * volatile x = malloc (32); + + free (x); // puts in tcache + free (x); // should abort + + printf("FAIL: tcache double free not detected\n"); + return 1; +} + +#define TEST_FUNCTION do_test +#define EXPECTED_SIGNAL SIGABRT +#include diff --git a/malloc/tst-tcfree2.c b/malloc/tst-tcfree2.c new file mode 100644 index 0000000000..2acc3036b5 --- /dev/null +++ b/malloc/tst-tcfree2.c @@ -0,0 +1,45 @@ +/* Copyright (C) 2018 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + . */ + +#include +#include +#include +#include +#include +#include +#include + +static int +do_test (void) +{ + char * volatile ptrs[20]; + int i; + +#define COUNT 20 + for (i=0; i diff --git a/manual/probes.texi b/manual/probes.texi index ab2a3102bb..0ea560ed78 100644 --- a/manual/probes.texi +++ b/manual/probes.texi @@ -243,6 +243,18 @@ This probe is triggered when the value of this tunable. @end deftp +@deftp Probe memory_tcache_double_free (void *@var{$arg1}, int @var{$arg2}) +This probe is triggered when @code{free} determines that the memory +being freed has probably already been freed, and resides in the +per-thread cache. Note that there is an extremely unlikely chance +that this probe will trigger due to random payload data remaining in +the allocated memory matching the key used to detect double frees. +This probe actually indicates that an expensive linear search of the +tcache, looking for a double free, has happened. Argument @var{$arg1} +is the memory location as passed to @code{free}, Argument @var{$arg2} +is the tcache bin it resides in. +@end deftp + @node Mathematical Function Probes @section Mathematical Function Probes