>Number: 155321
>Category: kern
>Synopsis: imgact_shell integer underflow when argv[0] is longer than
>interp + path
>Confidential: no
>Severity: serious
>Priority: high
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Sun Mar 06 20:00:18 UTC 2011
>Closed-Date:
>Last-Modified:
>Originator: Devon H. O'Dell
>Release: 8-STABLE
>Organization:
>Environment:
FreeBSD bigdisk.dho.apt 8.2-STABLE FreeBSD 8.2-STABLE #8: Sun Mar 6 14:20:26
EST 2011 r...@bigdisk.dho.apt:/usr/src/sys/amd64/compile/BIGDISK amd64
>Description:
In debugging a problem with Go calling execve(2), it appears that the actual
bug is in the FreeBSD kernel implementation in imgact_shell. Specifically, it
is entirely valid for argv[0] to be longer than the length of the path (treated
as "fname" in this function). We have a workaround in Go, but this should be
fixed in the kernel.
>How-To-Repeat:
Russ Cox wrote a quick to demonstrate the issue:
$ cat execve.c
#include <unistd.h>
#include <stdio.h>
int
main(int argc, char **argv, char **environ)
{
execve(argv[1], argv+2, environ);
perror("execve");
return 1;
}
$ cat shellscript
#!/bin/echo
$ gcc execve.c
$ cp /bin/ls .
$ ./a.out ls /bogus/ls
a.out execve.c ls shellscript
$ ./a.out shellscript asdf
shellscript
$ ./a.out shellscript /bogus/shellscript
shellscript
$ ./a.out shellscript /bin/echo-shellscript
shellscript
$ ./a.out shellscript /bin/echo-shellscript1
execve: Argument list too long
>Fix:
Patch attached.
Patch attached with submission follows:
Index: sys/kern/imgact_shell.c
===================================================================
--- sys/kern/imgact_shell.c (revision 219345)
+++ sys/kern/imgact_shell.c (working copy)
@@ -195,16 +195,19 @@
length = (imgp->args->argc == 0) ? 0 :
strlen(imgp->args->begin_argv) + 1; /* bytes to delete */
- if (offset - length > imgp->args->stringspace) {
- if (sname != NULL)
- sbuf_delete(sname);
- return (E2BIG);
+ if (offset >= length) {
+ if (offset - length > imgp->args->stringspace) {
+ if (sname != NULL)
+ sbuf_delete(sname);
+ return (E2BIG);
+ }
+
+ bcopy(imgp->args->begin_argv + length, imgp->args->begin_argv +
offset,
+ imgp->args->endp - (imgp->args->begin_argv + length));
+
+ offset -= length; /* calculate actual adjustment
*/
}
- bcopy(imgp->args->begin_argv + length, imgp->args->begin_argv + offset,
- imgp->args->endp - (imgp->args->begin_argv + length));
-
- offset -= length; /* calculate actual adjustment */
imgp->args->begin_envv += offset;
imgp->args->endp += offset;
imgp->args->stringspace -= offset;
>Release-Note:
>Audit-Trail:
>Unformatted:
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