diff mbox

[1/3] posix: Remove dynamic memory allocation from execl{e,p}

Message ID 1456146172-12850-2-git-send-email-adhemerval.zanella@linaro.org
State Superseded
Headers show

Commit Message

Adhemerval Zanella Feb. 22, 2016, 1:02 p.m. UTC 
GLIBC execl{e,p} implementation might use malloc if the total number of i
arguments exceed initial assumption size (1024).  This might lead to
issue in two situations:

1. execl/execle is stated to be async-signal-safe by POSIX [1].  However
   if execl is used in a signal handler with a large argument set (that
   may call malloc internally) and the resulting call fails, it might
   lead malloc in the program in a bad state.

2. If the functions are used in a vfork/clone(VFORK) situation it also
   might issue malloc internal bad state.

This patch fixes it by using stack allocation instead.  It also fixes
BZ#19534.

Tested on x86_64.

[1] http://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.html

	[BZ #19534]
	* posix/execl.c (execl): Remove dynamic memory allocation.
	* posix/execle.c (execle): Likewise.
	* posix/execlp.c (execlp): Likewise.
---
 posix/Makefile |  2 +-
 posix/execl.c  | 65 ++++++++++++++++---------------------------------------
 posix/execle.c | 66 +++++++++++++++++---------------------------------------
 posix/execlp.c | 68 ++++++++++++++++++++--------------------------------------
 5 files changed, 70 insertions(+), 138 deletions(-)

-- 
1.9.1

Comments

Adhemerval Zanella Feb. 25, 2016, 1:10 p.m. UTC | #1 
On 25-02-2016 04:27, Paul Eggert wrote:
> Adhemerval Zanella wrote:

>> +  int argc;

>> +  va_list ap;

>> +  va_start (ap, arg);

>> +  for (argc = 1; va_arg (ap, const char *); argc++)

>> +    continue;

> 

> With my "no arbitrary limits" hat on, I noticed that this has undefined behavior if more than INT_MAX arguments are passed to execl. The existing code is no saint in this area (it messes up badly if more than UINT_MAX args are passed), but the new code should not make things worse, and we might as well fix the UINT_MAX bug while we're at it.

> 


AFAIK the C standard defines the main entrypoint argc as signed int, so 
I think it is indeed undefined behaviour if you intend to call a program
with more than INT_MAX arguments.


> Attached please find a contrived test case illustrating the bug on x86-64. This test succeeds on x86-64 now (in that the program prints "execl: Cannot allocate memory" and exits with status 0) but could crash with the proposed patch. Perhaps you can add this to the glibc test cases while you're at it.

>
diff mbox

Patch

diff --git a/posix/Makefile b/posix/Makefile
index 4e90a95..55f4f31 100644
--- a/posix/Makefile
+++ b/posix/Makefile
@@ -221,8 +221,8 @@  CFLAGS-fexecve.os = -fomit-frame-pointer
 CFLAGS-execv.os = -fomit-frame-pointer
 CFLAGS-execle.os = -fomit-frame-pointer
 CFLAGS-execl.os = -fomit-frame-pointer
-CFLAGS-execvp.os = -fomit-frame-pointer
 CFLAGS-execlp.os = -fomit-frame-pointer
+CFLAGS-execvp.os = -fomit-frame-pointer
 
 tstgetopt-ARGS = -a -b -cfoobar --required foobar --optional=bazbug \
 		--none random --col --color --colour
diff --git a/posix/execl.c b/posix/execl.c
index 102d19d..cd40ff8 100644
--- a/posix/execl.c
+++ b/posix/execl.c
@@ -16,58 +16,31 @@ 
    <http://www.gnu.org/licenses/>.  */
 
 #include <unistd.h>
+#include <errno.h>
 #include <stdarg.h>
-#include <stddef.h>
-#include <stdlib.h>
-#include <string.h>
-
-#include <stackinfo.h>
-
+#include <sys/param.h>
 
 /* Execute PATH with all arguments after PATH until
    a NULL pointer and environment from `environ'.  */
 int
 execl (const char *path, const char *arg, ...)
 {
-#define INITIAL_ARGV_MAX 1024
-  size_t argv_max = INITIAL_ARGV_MAX;
-  const char *initial_argv[INITIAL_ARGV_MAX];
-  const char **argv = initial_argv;
-  va_list args;
-
-  argv[0] = arg;
-
-  va_start (args, arg);
-  unsigned int i = 0;
-  while (argv[i++] != NULL)
-    {
-      if (i == argv_max)
-	{
-	  argv_max *= 2;
-	  const char **nptr = realloc (argv == initial_argv ? NULL : argv,
-				       argv_max * sizeof (const char *));
-	  if (nptr == NULL)
-	    {
-	      if (argv != initial_argv)
-		free (argv);
-	      va_end (args);
-	      return -1;
-	    }
-	  if (argv == initial_argv)
-	    /* We have to copy the already filled-in data ourselves.  */
-	    memcpy (nptr, argv, i * sizeof (const char *));
-
-	  argv = nptr;
-	}
-
-      argv[i] = va_arg (args, const char *);
-    }
-  va_end (args);
-
-  int ret = __execve (path, (char *const *) argv, __environ);
-  if (argv != initial_argv)
-    free (argv);
-
-  return ret;
+  int argc;
+  va_list ap;
+  va_start (ap, arg);
+  for (argc = 1; va_arg (ap, const char *); argc++)
+    continue;
+  va_end (ap);
+
+  int i;
+  char *argv[argc + 1];
+  va_start (ap, arg);
+  argv[0] = (char *) arg;
+  for (i = 1; i < argc; i++)
+     argv[i] = va_arg (ap, char *);
+  argv[i] = NULL;
+  va_end (ap);
+
+  return __execve (path, argv, __environ);
 }
 libc_hidden_def (execl)
diff --git a/posix/execle.c b/posix/execle.c
index 8edc03a..17fc1d4 100644
--- a/posix/execle.c
+++ b/posix/execle.c
@@ -17,57 +17,31 @@ 
 
 #include <unistd.h>
 #include <stdarg.h>
-#include <stddef.h>
-#include <stdlib.h>
-#include <string.h>
-
-#include <stackinfo.h>
+#include <errno.h>
+#include <sys/param.h>
 
 /* Execute PATH with all arguments after PATH until a NULL pointer,
    and the argument after that for environment.  */
 int
 execle (const char *path, const char *arg, ...)
 {
-#define INITIAL_ARGV_MAX 1024
-  size_t argv_max = INITIAL_ARGV_MAX;
-  const char *initial_argv[INITIAL_ARGV_MAX];
-  const char **argv = initial_argv;
-  va_list args;
-  argv[0] = arg;
-
-  va_start (args, arg);
-  unsigned int i = 0;
-  while (argv[i++] != NULL)
-    {
-      if (i == argv_max)
-	{
-	  argv_max *= 2;
-	  const char **nptr = realloc (argv == initial_argv ? NULL : argv,
-				       argv_max * sizeof (const char *));
-	  if (nptr == NULL)
-	    {
-	      if (argv != initial_argv)
-		free (argv);
-	      va_end (args);
-	      return -1;
-	    }
-	  if (argv == initial_argv)
-	    /* We have to copy the already filled-in data ourselves.  */
-	    memcpy (nptr, argv, i * sizeof (const char *));
-
-	  argv = nptr;
-	}
-
-      argv[i] = va_arg (args, const char *);
-    }
-
-  const char *const *envp = va_arg (args, const char *const *);
-  va_end (args);
-
-  int ret = __execve (path, (char *const *) argv, (char *const *) envp);
-  if (argv != initial_argv)
-    free (argv);
-
-  return ret;
+  int argc;
+  va_list ap;
+  va_start (ap, arg);
+  for (argc = 1; va_arg (ap, const char *); argc++)
+    continue;
+  va_end (ap);
+
+  int i;
+  char *argv[argc + 1];
+  char **envp;
+  va_start (ap, arg);
+  argv[0] = (char *) arg;
+  for (i = 1; i <= argc; i++)
+     argv[i] = va_arg (ap, char *);
+  envp = va_arg (ap, char **);
+  va_end (ap);
+
+  return __execve (path, argv, envp);
 }
 libc_hidden_def (execle)
diff --git a/posix/execlp.c b/posix/execlp.c
index 6700994..0f789af 100644
--- a/posix/execlp.c
+++ b/posix/execlp.c
@@ -17,11 +17,8 @@ 
 
 #include <unistd.h>
 #include <stdarg.h>
-#include <stddef.h>
-#include <stdlib.h>
-#include <string.h>
-
-#include <stackinfo.h>
+#include <errno.h>
+#include <sys/param.h>
 
 /* Execute FILE, searching in the `PATH' environment variable if
    it contains no slashes, with all arguments after FILE until a
@@ -29,45 +26,26 @@ 
 int
 execlp (const char *file, const char *arg, ...)
 {
-#define INITIAL_ARGV_MAX 1024
-  size_t argv_max = INITIAL_ARGV_MAX;
-  const char *initial_argv[INITIAL_ARGV_MAX];
-  const char **argv = initial_argv;
-  va_list args;
-
-  argv[0] = arg;
-
-  va_start (args, arg);
-  unsigned int i = 0;
-  while (argv[i++] != NULL)
-    {
-      if (i == argv_max)
-	{
-	  argv_max *= 2;
-	  const char **nptr = realloc (argv == initial_argv ? NULL : argv,
-				       argv_max * sizeof (const char *));
-	  if (nptr == NULL)
-	    {
-	      if (argv != initial_argv)
-		free (argv);
-	      va_end (args);
-	      return -1;
-	    }
-	  if (argv == initial_argv)
-	    /* We have to copy the already filled-in data ourselves.  */
-	    memcpy (nptr, argv, i * sizeof (const char *));
-
-	  argv = nptr;
-	}
-
-      argv[i] = va_arg (args, const char *);
-    }
-  va_end (args);
-
-  int ret = execvp (file, (char *const *) argv);
-  if (argv != initial_argv)
-    free (argv);
-
-  return ret;
+  int argc;
+  va_list ap;
+  va_start (ap, arg);
+  for (argc = 1; va_arg (ap, const char *); argc++)
+    continue;
+  va_end (ap);
+
+  /* Although posix does not state execlp as an async-safe function
+     it can not use malloc to allocate the arguments since it might
+     be used in a vfork scenario and it may lead to malloc internal
+     bad state.  */
+  int i;
+  char *argv[argc + 1];
+  va_start (ap, arg);
+  argv[0] = (char *) arg;
+  for (i = 1; i < argc; i++)
+     argv[i] = va_arg (ap, char *);
+  argv[i] = NULL;
+  va_end (ap);
+
+  return __execvpe (file, argv, __environ);
 }
 libc_hidden_def (execlp)