From: P J P <ppandit@redhat.com>
To: Kees Cook <keescook@chromium.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Josh Triplett <josh@joshtriplett.org>,
Serge Hallyn <serge.hallyn@canonical.com>,
linux-fsdevel@vger.kernel.org, halfdog <me@halfdog.net>
Subject: Re: [PATCH] exec: do not leave bprm->interp on stack
Date: Sat, 24 Nov 2012 00:13:45 +0530 (IST) [thread overview]
Message-ID: <alpine.LFD.2.02.1211240004060.15883@wniryva.cad.erqung.pbz> (raw)
In-Reply-To: <CAGXu5jKY90dsnUjLcjC43Djoe53HEAffugtaEfsBphtp7j_A7g@mail.gmail.com>
Hello Kees, all,
Please have a look at a *NEW* patch at the end of this mail. It seems to fix
both the issues, stack disclosure + undue recursions.
It uses modprobe "--first-time" option which returns an error code when trying
to load a module which is already present or unload one which is not present.
Checking this return value at - request_module() - and breaking the loop in
case of an error seems to be doing the trick.
+-- On Mon, 19 Nov 2012, Kees Cook wrote --+
| I think to avoid the explosion of request_module calls in the abusive case,
| we could simply return ELOOP instead of ENOEXEC on max recursion.
-> http://www.spinics.net/lists/mm-commits/msg92433.html
1. returning -ELOOP has a side effect of not reaching to request_module()
ever, for:
==
#ifdef CONFIG_MODULES
1415 if (retval != -ENOEXEC || bprm->mm == NULL) {
1416 break;
1417 } else {
...
==
2. above patch does not seem to fix the 2^6(64) recursions issue, for:
==
+ bprm->recursion_depth = depth + 1;
retval = fn(bprm);
bprm->recursion_depth = depth;
==
setting - recursion_dept = depth - again and the outer for(try=0;try<2...)
loop seems to be causing the 2^6 recursions.
Please have a look at this *NEW* patch to fix both the issues, stack
disclosure + undue recursions.
===
diff --git a/fs/exec.c b/fs/exec.c
index 0039055..dec467f 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1423,7 +1423,14 @@ int search_binary_handler(struct linux_binprm *bprm,struct pt_regs *regs)
break; /* -ENOEXEC */
if (try)
break; /* -ENOEXEC */
- request_module("binfmt-%04x", *(unsigned short *)(&bprm->buf[2]));
+ if (request_module("binfmt-%04x",
+ *(unsigned short *)(&bprm->buf[2])))
+ {
+ printk(KERN_WARNING
+ "request_module: failed to load: binfmt-%04x",
+ *(unsigned short *)(&bprm->buf[2]));
+ break;
+ }
}
#else
break;
diff --git a/kernel/kmod.c b/kernel/kmod.c
index 1c317e3..7ec0e3e 100644
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -83,7 +83,7 @@ static int call_modprobe(char *module_name, int wait)
NULL
};
- char **argv = kmalloc(sizeof(char *[5]), GFP_KERNEL);
+ char **argv = kmalloc(sizeof(char *[6]), GFP_KERNEL);
if (!argv)
goto out;
@@ -93,9 +93,10 @@ static int call_modprobe(char *module_name, int wait)
argv[0] = modprobe_path;
argv[1] = "-q";
- argv[2] = "--";
- argv[3] = module_name; /* check free_modprobe_argv() */
- argv[4] = NULL;
+ argv[2] = "--first-time";
+ argv[3] = "--";
+ argv[4] = module_name; /* check free_modprobe_argv() */
+ argv[5] = NULL;
return call_usermodehelper_fns(modprobe_path, argv, envp,
wait | UMH_KILLABLE, NULL, free_modprobe_argv, NULL);
===
Thank you.
--
Prasad J Pandit / Red Hat Security Response Team
DB7A 84C5 D3F9 7CD1 B5EB C939 D048 7860 3655 602B
next prev parent reply other threads:[~2012-11-23 18:44 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-24 23:20 [PATCH] exec: do not leave bprm->interp on stack Kees Cook
2012-10-25 4:16 ` Al Viro
2012-10-25 6:21 ` Kees Cook
2012-10-25 11:46 ` P J P
2012-10-25 12:03 ` Tetsuo Handa
2012-10-25 12:57 ` P J P
2012-10-25 12:09 ` Al Viro
2012-10-25 12:38 ` Al Viro
2012-10-26 17:38 ` P J P
2012-10-26 18:36 ` Al Viro
2012-10-27 10:47 ` P J P
2012-10-27 17:05 ` Kees Cook
2012-10-27 20:16 ` P J P
2012-10-28 3:32 ` Kees Cook
2012-11-06 8:10 ` P J P
2012-11-12 22:10 ` Kees Cook
2012-11-13 6:50 ` halfdog
2012-11-16 12:50 ` P J P
2012-11-16 18:00 ` Kees Cook
2012-11-18 19:04 ` P J P
2012-11-18 19:34 ` Kees Cook
2012-11-19 6:57 ` P J P
2012-11-19 20:41 ` Kees Cook
2012-11-20 7:04 ` P J P
2012-11-22 20:06 ` P J P
2012-11-23 18:43 ` P J P [this message]
2012-11-23 23:12 ` Tetsuo Handa
[not found] ` <alpine.LFD.2.02.1211221934220.19768@wniryva.cad.erqung.pbz>
[not found] ` <CAGXu5jL8zCt5ghW4ODPL9+SyC9+mbuw=4JMUngepY5fC8pSikQ@mail.gmail.com>
2012-11-26 7:09 ` P J P
[not found] ` <CA+55aFx3LFH5Xj1OkNoy7vN5w8y5tH39MUDujKqF3BdnmYibLQ@mail.gmail.com>
2012-11-20 7:08 ` P J P
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