linux-kernel - [PATCH v2 7/8] exec: don't retry if request

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Date:	Mon, 5 Aug 2013 15:41:45 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Al Viro <viro@...IV.linux.org.uk>,
	Evgeniy Polyakov <zbr@...emap.net>,
	Kees Cook <keescook@...omium.org>,
	Zach Levis <zml@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 7/8] exec: don't retry if request_module() fails

A separate one-liner for better documentation.

It doesn't make sense to retry if request_module() fails to exec
/sbin/modprobe, add the additional "request_module() < 0" check.

However, this logic still doesn't look exactly right:

1. It would be better to check "request_module() != 0", the user
   space modprobe process should report the correct exit code.
   But I didn't dare to add the user-visible change.

2. The whole ENOEXEC logic looks suboptimal. Suppose that we try
   to exec a "#!path-to-unsupported-binary" script. In this case
   request_module() + "retry" will be done twice: first by the
   "depth == 1" code, and then again by the "depth == 0" caller
   which doesn't make sense.

3. And note that in the case above bprm->buf was already changed
   by load_script()->prepare_binprm(), so this looks even more
   ugly.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
Acked-by: Kees Cook <keescook@...omium.org>
---
 fs/exec.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index f69cf54..682895d 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1418,7 +1418,8 @@ int search_binary_handler(struct linux_binprm *bprm)
 		if (printable(bprm->buf[0]) && printable(bprm->buf[1]) &&
 		    printable(bprm->buf[2]) && printable(bprm->buf[3]))
 			return retval;
-		request_module("binfmt-%04x", *(ushort *)(bprm->buf + 2));
+		if (request_module("binfmt-%04x", *(ushort *)(bprm->buf + 2)) < 0)
+			return retval;
 		need_retry = false;
 		goto retry;
 	}
-- 
1.5.5.1

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