linux-kernel - Re: [PATCH][Resend v2] Fix infinite loop in search_binary

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Message-Id: <201107062028.JFH82378.OLQHFFMVJtFOSO@I-love.SAKURA.ne.jp>
Date:	Wed, 6 Jul 2011 20:28:18 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	richard@....at
Cc:	viro@...iv.linux.org.uk, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH][Resend v2] Fix infinite loop in search_binary_handler()

Richard Weinberger wrote:
> But IMHO adding a new attribute to task_struct is a bit overkill.
Indeed. I came up with a simpler solution. ;-)
----------------------------------------
[PATCH] exec: Do not call request_module() twice from search_binary_handler().

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>
---
diff --git a/fs/exec.c b/fs/exec.c
index 6075a1e..044c13f 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1411,6 +1411,8 @@ int search_binary_handler(struct linux_binprm *bprm,struct pt_regs *regs)
 			    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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