261 lines
8.4 KiB
Diff
261 lines
8.4 KiB
Diff
From 481a6cf0c24f02f251d7cd0b776c12d00e6b144f Mon Sep 17 00:00:00 2001
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From: DJ Delorie <dj@delorie.com>
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Date: Tue, 20 Nov 2018 13:24:09 -0500
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Subject: [PATCH 47] malloc: tcache double free check
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* malloc/malloc.c (tcache_entry): Add key field.
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(tcache_put): Set it.
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(tcache_get): Likewise.
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(_int_free): Check for double free in tcache.
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* malloc/tst-tcfree1.c: New.
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* malloc/tst-tcfree2.c: New.
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* malloc/Makefile: Run the new tests.
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* manual/probes.texi: Document memory_tcache_double_free probe.
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* dlfcn/dlerror.c (check_free): Prevent double frees.
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---
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ChangeLog | 12 +++++++++++
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dlfcn/dlerror.c | 5 ++++-
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malloc/Makefile | 1 +
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malloc/malloc.c | 28 ++++++++++++++++++++++++++
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malloc/tst-tcfree1.c | 42 ++++++++++++++++++++++++++++++++++++++
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malloc/tst-tcfree2.c | 48 ++++++++++++++++++++++++++++++++++++++++++++
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manual/probes.texi | 12 +++++++++++
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7 files changed, 147 insertions(+), 1 deletion(-)
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create mode 100644 malloc/tst-tcfree1.c
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create mode 100644 malloc/tst-tcfree2.c
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diff --git a/ChangeLog b/ChangeLog
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index 8c92ee7764..1ef4b4abe0 100644
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--- a/ChangeLog
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+++ b/ChangeLog
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@@ -1,3 +1,15 @@
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+2018-11-20 DJ Delorie <dj@redhat.com>
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+
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+ * malloc/malloc.c (tcache_entry): Add key field.
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+ (tcache_put): Set it.
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+ (tcache_get): Likewise.
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+ (_int_free): Check for double free in tcache.
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+ * malloc/tst-tcfree1.c: New.
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+ * malloc/tst-tcfree2.c: New.
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+ * malloc/Makefile: Run the new tests.
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+ * manual/probes.texi: Document memory_tcache_double_free probe.
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+
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+ * dlfcn/dlerror.c (check_free): Prevent double frees.
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2018-11-19 Florian Weimer <fweimer@redhat.com>
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support: Print timestamps in timeout handler.
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diff --git a/dlfcn/dlerror.c b/dlfcn/dlerror.c
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index 33574faab6..96bf925333 100644
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--- a/dlfcn/dlerror.c
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+++ b/dlfcn/dlerror.c
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@@ -198,7 +198,10 @@ check_free (struct dl_action_result *rec)
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Dl_info info;
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if (_dl_addr (check_free, &info, &map, NULL) != 0 && map->l_ns == 0)
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#endif
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- free ((char *) rec->errstring);
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+ {
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+ free ((char *) rec->errstring);
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+ rec->errstring = NULL;
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+ }
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}
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}
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diff --git a/malloc/Makefile b/malloc/Makefile
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index 7d54bad866..e6dfbfc14c 100644
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--- a/malloc/Makefile
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+++ b/malloc/Makefile
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@@ -38,6 +38,7 @@ tests := mallocbug tst-malloc tst-valloc tst-calloc tst-obstack \
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tst-malloc_info \
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tst-malloc-too-large \
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tst-malloc-stats-cancellation \
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+ tst-tcfree1 tst-tcfree2 \
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tests-static := \
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tst-interpose-static-nothread \
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diff --git a/malloc/malloc.c b/malloc/malloc.c
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index 47795601c8..6be2573868 100644
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--- a/malloc/malloc.c
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+++ b/malloc/malloc.c
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@@ -2888,6 +2888,8 @@ mremap_chunk (mchunkptr p, size_t new_size)
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typedef struct tcache_entry
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{
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struct tcache_entry *next;
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+ /* This field exists to detect double frees. */
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+ struct tcache_perthread_struct *key;
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} tcache_entry;
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/* There is one of these for each thread, which contains the
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@@ -2911,6 +2913,11 @@ tcache_put (mchunkptr chunk, size_t tc_idx)
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{
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tcache_entry *e = (tcache_entry *) chunk2mem (chunk);
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assert (tc_idx < TCACHE_MAX_BINS);
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+
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+ /* Mark this chunk as "in the tcache" so the test in _int_free will
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+ detect a double free. */
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+ e->key = tcache;
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+
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e->next = tcache->entries[tc_idx];
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tcache->entries[tc_idx] = e;
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++(tcache->counts[tc_idx]);
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@@ -2926,6 +2933,7 @@ tcache_get (size_t tc_idx)
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assert (tcache->entries[tc_idx] > 0);
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tcache->entries[tc_idx] = e->next;
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--(tcache->counts[tc_idx]);
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+ e->key = NULL;
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return (void *) e;
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}
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@@ -4166,6 +4174,26 @@ _int_free (mstate av, mchunkptr p, int have_lock)
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{
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size_t tc_idx = csize2tidx (size);
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+ /* Check to see if it's already in the tcache. */
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+ tcache_entry *e = (tcache_entry *) chunk2mem (p);
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+
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+ /* This test succeeds on double free. However, we don't 100%
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+ trust it (it also matches random payload data at a 1 in
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+ 2^<size_t> chance), so verify it's not an unlikely coincidence
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+ before aborting. */
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+ if (__glibc_unlikely (e->key == tcache && tcache))
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+ {
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+ tcache_entry *tmp;
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+ LIBC_PROBE (memory_tcache_double_free, 2, e, tc_idx);
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+ for (tmp = tcache->entries[tc_idx];
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+ tmp;
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+ tmp = tmp->next)
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+ if (tmp == e)
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+ malloc_printerr ("free(): double free detected in tcache 2");
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+ /* If we get here, it was a coincidence. We've wasted a few
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+ cycles, but don't abort. */
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+ }
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+
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if (tcache
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&& tc_idx < mp_.tcache_bins
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&& tcache->counts[tc_idx] < mp_.tcache_count)
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diff --git a/malloc/tst-tcfree1.c b/malloc/tst-tcfree1.c
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new file mode 100644
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index 0000000000..bc29375ce7
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--- /dev/null
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+++ b/malloc/tst-tcfree1.c
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@@ -0,0 +1,42 @@
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+/* Test that malloc tcache catches double free.
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+ Copyright (C) 2018 Free Software Foundation, Inc.
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+ This file is part of the GNU C Library.
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+
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+ The GNU C Library is free software; you can redistribute it and/or
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+ modify it under the terms of the GNU Lesser General Public
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+ License as published by the Free Software Foundation; either
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+ version 2.1 of the License, or (at your option) any later version.
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+
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+ The GNU C Library is distributed in the hope that it will be useful,
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+ but WITHOUT ANY WARRANTY; without even the implied warranty of
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+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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+ Lesser General Public License for more details.
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+
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+ You should have received a copy of the GNU Lesser General Public
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+ License along with the GNU C Library; if not, see
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+ <http://www.gnu.org/licenses/>. */
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+
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+#include <errno.h>
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+#include <error.h>
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+#include <limits.h>
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+#include <malloc.h>
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+#include <stdlib.h>
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+#include <stdio.h>
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+#include <sys/signal.h>
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+
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+static int
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+do_test (void)
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+{
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+ /* Do one allocation of any size that fits in tcache. */
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+ char * volatile x = malloc (32);
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+
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+ free (x); // puts in tcache
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+ free (x); // should abort
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+
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+ printf("FAIL: tcache double free not detected\n");
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+ return 1;
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+}
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+
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+#define TEST_FUNCTION do_test
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+#define EXPECTED_SIGNAL SIGABRT
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+#include <support/test-driver.c>
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diff --git a/malloc/tst-tcfree2.c b/malloc/tst-tcfree2.c
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new file mode 100644
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index 0000000000..17f06bacd4
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--- /dev/null
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+++ b/malloc/tst-tcfree2.c
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@@ -0,0 +1,48 @@
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+/* Test that malloc tcache catches double free.
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+ Copyright (C) 2018 Free Software Foundation, Inc.
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+ This file is part of the GNU C Library.
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+
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+ The GNU C Library is free software; you can redistribute it and/or
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+ modify it under the terms of the GNU Lesser General Public
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+ License as published by the Free Software Foundation; either
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+ version 2.1 of the License, or (at your option) any later version.
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+
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+ The GNU C Library is distributed in the hope that it will be useful,
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+ but WITHOUT ANY WARRANTY; without even the implied warranty of
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+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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+ Lesser General Public License for more details.
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+
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+ You should have received a copy of the GNU Lesser General Public
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+ License along with the GNU C Library; if not, see
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+ <http://www.gnu.org/licenses/>. */
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+
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+#include <errno.h>
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+#include <error.h>
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+#include <limits.h>
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+#include <malloc.h>
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+#include <stdlib.h>
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+#include <stdio.h>
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+#include <sys/signal.h>
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+
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+static int
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+do_test (void)
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+{
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+ char * volatile ptrs[20];
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+ int i;
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+
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+ /* Allocate enough small chunks so that when we free them all, the tcache
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+ is full, and the first one we freed is at the end of its linked list. */
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+#define COUNT 20
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+ for (i=0; i<COUNT; i++)
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+ ptrs[i] = malloc (20);
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+ for (i=0; i<COUNT; i++)
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+ free (ptrs[i]);
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+ free (ptrs[0]);
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+
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+ printf("FAIL: tcache double free\n");
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+ return 1;
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+}
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+
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+#define TEST_FUNCTION do_test
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+#define EXPECTED_SIGNAL SIGABRT
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+#include <support/test-driver.c>
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diff --git a/manual/probes.texi b/manual/probes.texi
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index ab2a3102bb..0ea560ed78 100644
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--- a/manual/probes.texi
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+++ b/manual/probes.texi
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@@ -243,6 +243,18 @@ This probe is triggered when the
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value of this tunable.
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@end deftp
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+@deftp Probe memory_tcache_double_free (void *@var{$arg1}, int @var{$arg2})
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+This probe is triggered when @code{free} determines that the memory
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+being freed has probably already been freed, and resides in the
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+per-thread cache. Note that there is an extremely unlikely chance
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+that this probe will trigger due to random payload data remaining in
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+the allocated memory matching the key used to detect double frees.
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+This probe actually indicates that an expensive linear search of the
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+tcache, looking for a double free, has happened. Argument @var{$arg1}
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+is the memory location as passed to @code{free}, Argument @var{$arg2}
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+is the tcache bin it resides in.
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+@end deftp
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+
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@node Mathematical Function Probes
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@section Mathematical Function Probes
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