linux-kernel - Re: [PATCH v6 04/15] memory-hotplug: remove /sys/firmware/memmap/X sysfs

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20130109151920.fb9b4029.akpm@linux-foundation.org>
Date:	Wed, 9 Jan 2013 15:19:20 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Tang Chen <tangchen@...fujitsu.com>
Cc:	rientjes@...gle.com, len.brown@...el.com, benh@...nel.crashing.org,
	paulus@...ba.org, cl@...ux.com, minchan.kim@...il.com,
	kosaki.motohiro@...fujitsu.com, isimatu.yasuaki@...fujitsu.com,
	wujianguo@...wei.com, wency@...fujitsu.com, hpa@...or.com,
	linfeng@...fujitsu.com, laijs@...fujitsu.com, mgorman@...e.de,
	yinghai@...nel.org, glommer@...allels.com, x86@...nel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-acpi@...r.kernel.org,
	linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
	linux-ia64@...r.kernel.org, cmetcalf@...era.com,
	sparclinux@...r.kernel.org
Subject: Re: [PATCH v6 04/15] memory-hotplug: remove /sys/firmware/memmap/X
 sysfs

On Wed, 9 Jan 2013 17:32:28 +0800
Tang Chen <tangchen@...fujitsu.com> wrote:

> From: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
> 
> When (hot)adding memory into system, /sys/firmware/memmap/X/{end, start, type}
> sysfs files are created. But there is no code to remove these files. The patch
> implements the function to remove them.
> 
> Note: The code does not free firmware_map_entry which is allocated by bootmem.
>       So the patch makes memory leak. But I think the memory leak size is
>       very samll. And it does not affect the system.
> 
> ...
>
> +static struct firmware_map_entry * __meminit
> +firmware_map_find_entry(u64 start, u64 end, const char *type)
> +{
> +	struct firmware_map_entry *entry;
> +
> +	spin_lock(&map_entries_lock);
> +	list_for_each_entry(entry, &map_entries, list)
> +		if ((entry->start == start) && (entry->end == end) &&
> +		    (!strcmp(entry->type, type))) {
> +			spin_unlock(&map_entries_lock);
> +			return entry;
> +		}
> +
> +	spin_unlock(&map_entries_lock);
> +	return NULL;
> +}
>
> ...
>
> +	entry = firmware_map_find_entry(start, end - 1, type);
> +	if (!entry)
> +		return -EINVAL;
> +
> +	firmware_map_remove_entry(entry);
>
> ...
>

The above code looks racy.  After firmware_map_find_entry() does the
spin_unlock() there is nothing to prevent a concurrent
firmware_map_remove_entry() from removing the entry, so the kernel ends
up calling firmware_map_remove_entry() twice against the same entry.

An easy fix for this is to hold the spinlock across the entire
lookup/remove operation.


This problem is inherent to firmware_map_find_entry() as you have
implemented it, so this function simply should not exist in the current
form - no caller can use it without being buggy!  A simple fix for this
is to remove the spin_lock()/spin_unlock() from
firmware_map_find_entry() and add locking documentation to
firmware_map_find_entry(), explaining that the caller must hold
map_entries_lock and must not release that lock until processing of
firmware_map_find_entry()'s return value has completed.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/