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>

1 files changed, 14 insertions, 1 deletions

diff --git a/gmon/Makefile b/gmon/Makefile
index 83837dd689..213622a7ad 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)