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

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Date:	Thu, 07 Jul 2011 13:04:34 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	akpm@...ux-foundation.org
Cc:	richard@....at, viro@...iv.linux.org.uk,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH][Resend v2] Fix infinite loop in search_binary_handler()

Andrew Morton wrote:
> What is that "for (try=0; try<2" loop actually there for?  To retry
> after the request_module(), it appears.  Which is pointless if
> !CONFIG_MODULES.

Indeed. This loop was introduced in Linux 1.3.57 (where CONFIG_KERNELD was
introduced). Comparing between 1.3.56 and 1.3.57, there is no reason to retry
if !CONFIG_KERNELD, for get_fs_type() in fs/super.c and dev_get() in
net/core/dev.c do not retry if !CONFIG_KERNELD.

struct file_system_type *get_fs_type(const char *name)
{
	struct file_system_type * fs = file_systems;
	
	if (!name)
		return fs;
	for (fs = file_systems; fs && strcmp(fs->name, name); fs = fs->next)
		;
#ifdef CONFIG_KERNELD
	if (!fs && (request_module(name) == 0)) {
		for (fs = file_systems; fs && strcmp(fs->name, name); fs = fs->next)
			;
	}
#endif

	return fs;
}

struct device *dev_get(const char *name)
{
	struct device *dev;

	for (dev = dev_base; dev != NULL; dev = dev->next) 
	{
		if (strcmp(dev->name, name) == 0)
			return(dev);
	}
#ifdef CONFIG_KERNELD
	if (request_module(name) == 0)
		for (dev = dev_base; dev != NULL; dev = dev->next) {
			if (strcmp(dev->name, name) == 0)
				return(dev);
		}
#endif
	return(NULL);
}

It is likely that we have been doing needless retry if !CONFIG_MODULES.
----------------------------------------
[PATCH] exec: Do not retry load_binary method if CONFIG_MODULES=n.

If CONFIG_MODULES=n, it makes no sense to retry the list of binary formats
handler because the list will not be modified by request_module().

Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
---
diff --git a/fs/exec.c b/fs/exec.c
index 6075a1e..46c399f 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1401,9 +1401,9 @@ int search_binary_handler(struct linux_binprm *bprm,struct pt_regs *regs)
 			}
 		}
 		read_unlock(&binfmt_lock);
+#ifdef CONFIG_MODULES
 		if (retval != -ENOEXEC || bprm->mm == NULL) {
 			break;
-#ifdef CONFIG_MODULES
 		} else {
 #define printable(c) (((c)=='\t') || ((c)=='\n') || (0x20<=(c) && (c)<=0x7e))
 			if (printable(bprm->buf[0]) &&
@@ -1412,8 +1412,10 @@ int search_binary_handler(struct linux_binprm *bprm,struct pt_regs *regs)
 			    printable(bprm->buf[3]))
 				break; /* -ENOEXEC */
 			request_module("binfmt-%04x", *(unsigned short *)(&bprm->buf[2]));
-#endif
 		}
+#else
+		break;
+#endif
 	}
 	return retval;
 }
--
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