diff mbox

Fix segfault in maybe_script_execute.

Message ID f69c7e70-b0b0-b635-1582-0a3ad36de981@linux.ibm.com
State Superseded
Headers show

Commit Message

Stefan Liebler Sept. 6, 2018, 9:06 a.m. UTC
On 09/06/2018 10:50 AM, Andreas Schwab wrote:
> On Sep 06 2018, Stefan Liebler <stli@linux.ibm.com> wrote:
> 
>> On 09/05/2018 03:44 PM, Andreas Schwab wrote:
>>> On Sep 05 2018, Stefan Liebler <stli@linux.ibm.com> wrote:
>>>
>>>> If argc > 1, the arguments inclusive the NULL termination of new_argv
>>>> is copied from argv with memcpy.
>>>
>>> But it has the same bug, doesn't it?
>>>
>>> Andreas.
>>>
>> Yes. It also has this bug.
> 
> This makes the description rather confusing, implying there is a
> difference between argc == 1 and argc > 1, which isn't.
> 
> Andreas.
> 
Okay. I've adjusted the description.

Thanks.
Stefan

Comments

Andreas Schwab Sept. 6, 2018, 9:14 a.m. UTC | #1
On Sep 06 2018, Stefan Liebler <stli@linux.ibm.com> wrote:

> commit 6359e1c59f856a1115fdbcfa233052ac62e32c83
> Author: Stefan Liebler <stli@linux.ibm.com>
> Date:   Thu Sep 6 11:03:38 2018 +0200
>
>     Fix segfault in maybe_script_execute.
>     
>     If glibc is built with gcc 8 and -march=z900,
>     the testcase posix/tst-spawn4-compat crashes with a segfault.
>     
>     In function maybe_script_execute, the new_argv array is dynamically
>     initialized on stack with (argc + 1) elements.
>     The function wants to add _PATH_BSHELL as the first argument
>     and writes out of bounds of new_argv.
>     
>     In case of argc == 1, it writes three instead of two elements:
>     new_argv[0] = (char *) _PATH_BSHELL;
>     new_argv[1] = (char *) args->file;
>     new_argv[2] = NULL;
>     
>     The latter write access writes to the same location where the
>     pointer args is stored on stack.  Then it segfaults while accessing args:
>     args->exec (new_argv[0], new_argv, args->envp);
>     
>     In case of argc > 1, new_argv[0] and new_argv[1] are set in the same

This still make a difference between argc == 1 and argc > 1.  Just say
that there is an off-by-one because maybe_script_execute fails to count
the terminating NULL when sizing new_argv.

Andreas.
diff mbox

Patch

commit 6359e1c59f856a1115fdbcfa233052ac62e32c83
Author: Stefan Liebler <stli@linux.ibm.com>
Date:   Thu Sep 6 11:03:38 2018 +0200

    Fix segfault in maybe_script_execute.
    
    If glibc is built with gcc 8 and -march=z900,
    the testcase posix/tst-spawn4-compat crashes with a segfault.
    
    In function maybe_script_execute, the new_argv array is dynamically
    initialized on stack with (argc + 1) elements.
    The function wants to add _PATH_BSHELL as the first argument
    and writes out of bounds of new_argv.
    
    In case of argc == 1, it writes three instead of two elements:
    new_argv[0] = (char *) _PATH_BSHELL;
    new_argv[1] = (char *) args->file;
    new_argv[2] = NULL;
    
    The latter write access writes to the same location where the
    pointer args is stored on stack.  Then it segfaults while accessing args:
    args->exec (new_argv[0], new_argv, args->envp);
    
    In case of argc > 1, new_argv[0] and new_argv[1] are set in the same
    way as in the case above and the arguments inclusive the NULL termination
    of new_argv is copied from argv with memcpy.
    Note: The last copied element (NULL termination) is written out of
    bounds of new_argv.
    
    The implementation assumes that argc == 0 will never happen!
    
    ChangeLog:
    
            * sysdeps/unix/sysv/linux/spawni.c (maybe_script_execute):
            Increment size of new_argv by one.

diff --git a/sysdeps/unix/sysv/linux/spawni.c b/sysdeps/unix/sysv/linux/spawni.c
index cf0213ece5..85239cedbf 100644
--- a/sysdeps/unix/sysv/linux/spawni.c
+++ b/sysdeps/unix/sysv/linux/spawni.c
@@ -101,7 +101,7 @@  maybe_script_execute (struct posix_spawn_args *args)
       ptrdiff_t argc = args->argc;
 
       /* Construct an argument list for the shell.  */
-      char *new_argv[argc + 1];
+      char *new_argv[argc + 2];
       new_argv[0] = (char *) _PATH_BSHELL;
       new_argv[1] = (char *) args->file;
       if (argc > 1)