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Btrfs: use rcu to protect device->name
Al pointed out that we can just toss out the old name on a device and add a new one arbitrarily, so anybody who uses device->name in printk could possibly use free'd memory. Instead of adding locking around all of this he suggested doing it with RCU, so I've introduced a struct rcu_string that does just that and have gone through and protected all accesses to device->name that aren't under the uuid_mutex with rcu_read_lock(). This protects us and I will use it for dealing with removing the device that we used to mount the file system in a later patch. Thanks, Reviewed-by: David Sterba <dsterba@suse.cz> Signed-off-by: Josef Bacik <josef@redhat.com>
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,56 @@ | ||
| /* | ||
| * Copyright (C) 2012 Red Hat. All rights reserved. | ||
| * | ||
| * This program is free software; you can redistribute it and/or | ||
| * modify it under the terms of the GNU General Public | ||
| * License v2 as published by the Free Software Foundation. | ||
| * | ||
| * This program is distributed in the hope that it will be useful, | ||
| * but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
| * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | ||
| * General Public License for more details. | ||
| * | ||
| * You should have received a copy of the GNU General Public | ||
| * License along with this program; if not, write to the | ||
| * Free Software Foundation, Inc., 59 Temple Place - Suite 330, | ||
| * Boston, MA 021110-1307, USA. | ||
| */ | ||
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| struct rcu_string { | ||
| struct rcu_head rcu; | ||
| char str[0]; | ||
| }; | ||
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| static inline struct rcu_string *rcu_string_strdup(const char *src, gfp_t mask) | ||
| { | ||
| size_t len = strlen(src) + 1; | ||
| struct rcu_string *ret = kzalloc(sizeof(struct rcu_string) + | ||
| (len * sizeof(char)), mask); | ||
| if (!ret) | ||
| return ret; | ||
| strncpy(ret->str, src, len); | ||
| return ret; | ||
| } | ||
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| static inline void rcu_string_free(struct rcu_string *str) | ||
| { | ||
| if (str) | ||
| kfree_rcu(str, rcu); | ||
| } | ||
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| #define printk_in_rcu(fmt, ...) do { \ | ||
| rcu_read_lock(); \ | ||
| printk(fmt, __VA_ARGS__); \ | ||
| rcu_read_unlock(); \ | ||
| } while (0) | ||
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| #define printk_ratelimited_in_rcu(fmt, ...) do { \ | ||
| rcu_read_lock(); \ | ||
| printk_ratelimited(fmt, __VA_ARGS__); \ | ||
| rcu_read_unlock(); \ | ||
| } while (0) | ||
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| #define rcu_str_deref(rcu_str) ({ \ | ||
| struct rcu_string *__str = rcu_dereference(rcu_str); \ | ||
| __str->str; \ | ||
| }) |
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