gmon: fix memory corruption issues [BZ# 30101]

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>
Reviewed-by: DJ Delorie <dj@redhat.com>

3 files changed, 64 insertions, 8 deletions

diff --git a/gmon/Makefile b/gmon/Makefile
index 83837dd..213622a 100644
--- a/gmon/Makefile
+++ b/gmon/Makefile
@@ -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 tst-mcount-overflow
+tests	= tst-sprofil tst-gmon tst-mcount-overflow tst-mcleanup
 ifeq ($(build-profile),yes)
 tests	+= tst-profile-static
 tests-static	+= tst-profile-static
@@ -68,6 +69,14 @@ ifeq ($(run-built-tests),yes)
 tests-special += $(objpfx)tst-mcount-overflow-check.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
@@ -123,6 +132,10 @@ $(objpfx)tst-mcount-overflow-check.out: tst-mcount-overflow-check.sh $(objpfx)ts
 	$(SHELL) $< $(objpfx)tst-mcount-overflow > $@; \
 	$(evaluate-test)
 
+$(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)
diff --git a/gmon/gmon.c b/gmon/gmon.c
index 689bf80..5e99a73 100644
--- a/gmon/gmon.c
+++ b/gmon/gmon.c
@@ -102,11 +102,8 @@ __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);
@@ -116,7 +113,9 @@ __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)
@@ -147,6 +146,14 @@ __monstartup (u_long lowpc, u_long highpc)
 #endif
 
   /*
+   * 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.
    */
@@ -463,9 +470,14 @@ _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;
 }
diff --git a/gmon/tst-mcleanup.c b/gmon/tst-mcleanup.c
new file mode 100644
index 0000000..b259653
--- /dev/null
+++ b/gmon/tst-mcleanup.c
@@ -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;
+}