[v2] gmon: fix memory corruption issues [BZ# 30101]
Checks
| Context |
Check |
Description |
| dj/TryBot-apply_patch |
success
|
Patch applied to master at the time it was sent
|
| dj/TryBot-32bit |
success
|
Build for i686
|
Commit Message
V2 of this patch fixes an issue in V1, where the state was changed to ON not
OFF at end of _mcleanup. I hadn't noticed that (counterintuitively) ON=0 and
OFF=3, hence zeroing the buffer turned it back on. So set the state to OFF
after the memset.
1. Prevent double free, and reads from unallocated memory, when
_mcleanup is (incorrectly) called two or more times in a row,
without an intervening call to __monstartup; with this patch, the
second and subsequent calls effectively become no-ops instead.
While setting tos=NULL is minimal fix, safest action is to zero the
whole gmonparam buffer.
2. Prevent memory leak when __monstartup is (incorrectly) called two
or more times in a row, without an intervening call to _mcleanup;
with this patch, the second and subsequent calls effectively become
no-ops instead.
3. After _mcleanup, treat __moncontrol(1) as __moncontrol(0) instead.
With zeroing of gmonparam buffer in _mcleanup, this stops the
state incorrectly being changed to GMON_PROF_ON despite profiling
actually being off. If we'd just done the minimal fix to _mcleanup
of setting tos=NULL, there is risk of far worse memory corruption:
kcount would point to deallocated memory, and the __profil syscall
would make the kernel write profiling data into that memory,
which could have since been reallocated to something unrelated.
4. Ensure __moncontrol(0) still turns off profiling even in error
state. Otherwise, if mcount overflows and sets state to
GMON_PROF_ERROR, when _mcleanup calls __moncontrol(0), the __profil
syscall to disable profiling will not be invoked. _mcleanup will
free the buffer, but the kernel will still be writing profiling
data into it, potentially corrupted arbitrary memory.
Also adds a test case for (1). Issues (2)-(4) are not feasible to test.
Signed-off-by: Simon Kissane <skissane@gmail.com>
---
gmon/Makefile | 15 ++++++++++++++-
gmon/gmon.c | 26 +++++++++++++++++++-------
gmon/tst-mcleanup.c | 31 +++++++++++++++++++++++++++++++
3 files changed, 64 insertions(+), 8 deletions(-)
create mode 100644 gmon/tst-mcleanup.c
Comments
LGTM.
Reviewed-by: DJ Delorie <dj@redhat.com>
Hearing no further discussion on this one in a week, I pushed it.
Thanks!
@@ -1,4 +1,5 @@
# Copyright (C) 1995-2023 Free Software Foundation, Inc.
+# Copyright The GNU Toolchain Authors.
# This file is part of the GNU C Library.
# The GNU C Library is free software; you can redistribute it and/or
@@ -25,7 +26,7 @@ include ../Makeconfig
headers := sys/gmon.h sys/gmon_out.h sys/profil.h
routines := gmon mcount profil sprofil prof-freq
-tests = tst-sprofil tst-gmon
+tests = tst-sprofil tst-gmon tst-mcleanup
ifeq ($(build-profile),yes)
tests += tst-profile-static
tests-static += tst-profile-static
@@ -56,6 +57,14 @@ ifeq ($(run-built-tests),yes)
tests-special += $(objpfx)tst-gmon-gprof.out
endif
+CFLAGS-tst-mcleanup.c := -fno-omit-frame-pointer -pg
+tst-mcleanup-no-pie = yes
+CRT-tst-mcleanup := $(csu-objpfx)g$(start-installed-name)
+tst-mcleanup-ENV := GMON_OUT_PREFIX=$(objpfx)tst-mcleanup.data
+ifeq ($(run-built-tests),yes)
+tests-special += $(objpfx)tst-mcleanup.out
+endif
+
CFLAGS-tst-gmon-static.c := $(PIE-ccflag) -fno-omit-frame-pointer -pg
CRT-tst-gmon-static := $(csu-objpfx)g$(static-start-installed-name)
tst-gmon-static-no-pie = yes
@@ -103,6 +112,10 @@ $(objpfx)tst-gmon.out: clean-tst-gmon-data
clean-tst-gmon-data:
rm -f $(objpfx)tst-gmon.data.*
+$(objpfx)tst-mcleanup.out: clean-tst-mcleanup-data
+clean-tst-mcleanup-data:
+ rm -f $(objpfx)tst-mcleanup.data.*
+
$(objpfx)tst-gmon-gprof.out: tst-gmon-gprof.sh $(objpfx)tst-gmon.out
$(SHELL) $< $(GPROF) $(objpfx)tst-gmon $(objpfx)tst-gmon.data.* > $@; \
$(evaluate-test)
@@ -97,11 +97,8 @@ __moncontrol (int mode)
{
struct gmonparam *p = &_gmonparam;
- /* Don't change the state if we ran into an error. */
- if (p->state == GMON_PROF_ERROR)
- return;
-
- if (mode)
+ /* Treat start request as stop if error or gmon not initialized. */
+ if (mode && p->state != GMON_PROF_ERROR && p->tos != NULL)
{
/* start */
__profil((void *) p->kcount, p->kcountsize, p->lowpc, s_scale);
@@ -111,7 +108,9 @@ __moncontrol (int mode)
{
/* stop */
__profil(NULL, 0, 0, 0);
- p->state = GMON_PROF_OFF;
+ /* Don't change the state if we ran into an error. */
+ if (p->state != GMON_PROF_ERROR)
+ p->state = GMON_PROF_OFF;
}
}
libc_hidden_def (__moncontrol)
@@ -125,6 +124,14 @@ __monstartup (u_long lowpc, u_long highpc)
char *cp;
struct gmonparam *p = &_gmonparam;
+ /*
+ * If we are incorrectly called twice in a row (without an
+ * intervening call to _mcleanup), ignore the second call to
+ * prevent leaking memory.
+ */
+ if (p->tos != NULL)
+ return;
+
/*
* round lowpc and highpc to multiples of the density we're using
* so the rest of the scaling (here and in gprof) stays in ints.
@@ -440,9 +447,14 @@ _mcleanup (void)
{
__moncontrol (0);
- if (_gmonparam.state != GMON_PROF_ERROR)
+ if (_gmonparam.state != GMON_PROF_ERROR && _gmonparam.tos != NULL)
write_gmon ();
/* free the memory. */
free (_gmonparam.tos);
+
+ /* reset buffer to initial state for safety */
+ memset(&_gmonparam, 0, sizeof _gmonparam);
+ /* somewhat confusingly, ON=0, OFF=3 */
+ _gmonparam.state = GMON_PROF_OFF;
}
new file mode 100644
@@ -0,0 +1,31 @@
+/* Test program for repeated invocation of _mcleanup
+ Copyright The GNU Toolchain Authors.
+ 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
+ <https://www.gnu.org/licenses/>. */
+
+/* Intentionally calls _mcleanup() twice: once manually, it will be
+ called again as an atexit handler. This is incorrect use of the API,
+ but the point of the test is to make sure we don't crash when the
+ API is misused in this way. */
+
+#include <sys/gmon.h>
+
+int
+main (void)
+{
+ _mcleanup();
+ return 0;
+}