linux-kernel - [28/38] exec: do not call request_module() twice from search_binary

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Message-Id: <20111011165712.614913168@pistachio.kroah.org>
Date:	Tue, 11 Oct 2011 10:55:38 -0600
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Al Viro <viro@...iv.linux.org.uk>,
	Maxim Uvarov <muvarov@...il.com>
Subject: [28/38] exec: do not call request_module() twice from search_binary_handler()

3.0-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>

commit 912193521b719fbfc2f16776febf5232fe8ba261 upstream.

Currently, search_binary_handler() tries to load binary loader module
using request_module() if a loader for the requested program is not yet
loaded.  But second attempt of request_module() does not affect the result
of search_binary_handler().

If request_module() triggered recursion, calling request_module() twice
causes 2 to the power of MAX_KMOD_CONCURRENT (= 50) repetitions.  It is
not an infinite loop but is sufficient for users to consider as a hang up.

Therefore, this patch changes not to call request_module() twice, making 1
to the power of MAX_KMOD_CONCURRENT repetitions in case of recursion.

Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Reported-by: Richard Weinberger <richard@....at>
Tested-by: Richard Weinberger <richard@....at>
Cc: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Cc: Maxim Uvarov <muvarov@...il.com>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>

---
 fs/exec.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1411,6 +1411,8 @@ int search_binary_handler(struct linux_b
 			    printable(bprm->buf[2]) &&
 			    printable(bprm->buf[3]))
 				break; /* -ENOEXEC */
+			if (try)
+				break; /* -ENOEXEC */
 			request_module("binfmt-%04x", *(unsigned short *)(&bprm->buf[2]));
 #endif
 		}


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