https://github.com/torvalds/linux
Revision 95dd77580ccd66a0da96e6d4696945b8cea39431 authored by Eric W. Biederman on 14 March 2018, 23:20:29 UTC, committed by Al Viro on 15 March 2018, 22:48:38 UTC
On nfsv2 and nfsv3 the nfs server can export subsets of the same
filesystem and report the same filesystem identifier, so that the nfs
client can know they are the same filesystem. The subsets can be from
disjoint directory trees. The nfsv2 and nfsv3 filesystems provides no
way to find the common root of all directory trees exported form the
server with the same filesystem identifier.
The practical result is that in struct super s_root for nfs s_root is
not necessarily the root of the filesystem. The nfs mount code sets
s_root to the root of the first subset of the nfs filesystem that the
kernel mounts.
This effects the dcache invalidation code in generic_shutdown_super
currently called shrunk_dcache_for_umount and that code for years
has gone through an additional list of dentries that might be dentry
trees that need to be freed to accomodate nfs.
When I wrote path_connected I did not realize nfs was so special, and
it's hueristic for avoiding calling is_subdir can fail.
The practical case where this fails is when there is a move of a
directory from the subtree exposed by one nfs mount to the subtree
exposed by another nfs mount. This move can happen either locally or
remotely. With the remote case requiring that the move directory be cached
before the move and that after the move someone walks the path
to where the move directory now exists and in so doing causes the
already cached directory to be moved in the dcache through the magic
of d_splice_alias.
If someone whose working directory is in the move directory or a
subdirectory and now starts calling .. from the initial mount of nfs
(where s_root == mnt_root), then path_connected as a heuristic will
not bother with the is_subdir check. As s_root really is not the root
of the nfs filesystem this heuristic is wrong, and the path may
actually not be connected and path_connected can fail.
The is_subdir function might be cheap enough that we can call it
unconditionally. Verifying that will take some benchmarking and
the result may not be the same on all kernels this fix needs
to be backported to. So I am avoiding that for now.
Filesystems with snapshots such as nilfs and btrfs do something
similar. But as the directory tree of the snapshots are disjoint
from one another and from the main directory tree rename won't move
things between them and this problem will not occur.
Cc: stable@vger.kernel.org
Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
Fixes: 397d425dc26d ("vfs: Test for and handle paths that are unreachable from their mnt_root")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
1 parent 8cc07c8
Tip revision: 95dd77580ccd66a0da96e6d4696945b8cea39431 authored by Eric W. Biederman on 14 March 2018, 23:20:29 UTC
fs: Teach path_connected to handle nfs filesystems with multiple roots.
fs: Teach path_connected to handle nfs filesystems with multiple roots.
Tip revision: 95dd775
internal.h
/*
* Cryptographic API.
*
* Copyright (c) 2002 James Morris <jmorris@intercode.com.au>
* Copyright (c) 2005 Herbert Xu <herbert@gondor.apana.org.au>
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the Free
* Software Foundation; either version 2 of the License, or (at your option)
* any later version.
*
*/
#ifndef _CRYPTO_INTERNAL_H
#define _CRYPTO_INTERNAL_H
#include <crypto/algapi.h>
#include <linux/completion.h>
#include <linux/mm.h>
#include <linux/highmem.h>
#include <linux/interrupt.h>
#include <linux/init.h>
#include <linux/list.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/notifier.h>
#include <linux/rwsem.h>
#include <linux/slab.h>
/* Crypto notification events. */
enum {
CRYPTO_MSG_ALG_REQUEST,
CRYPTO_MSG_ALG_REGISTER,
};
struct crypto_instance;
struct crypto_template;
struct crypto_larval {
struct crypto_alg alg;
struct crypto_alg *adult;
struct completion completion;
u32 mask;
};
extern struct list_head crypto_alg_list;
extern struct rw_semaphore crypto_alg_sem;
extern struct blocking_notifier_head crypto_chain;
#ifdef CONFIG_PROC_FS
void __init crypto_init_proc(void);
void __exit crypto_exit_proc(void);
#else
static inline void crypto_init_proc(void)
{ }
static inline void crypto_exit_proc(void)
{ }
#endif
static inline unsigned int crypto_cipher_ctxsize(struct crypto_alg *alg)
{
return alg->cra_ctxsize;
}
static inline unsigned int crypto_compress_ctxsize(struct crypto_alg *alg)
{
return alg->cra_ctxsize;
}
struct crypto_alg *crypto_mod_get(struct crypto_alg *alg);
struct crypto_alg *crypto_alg_lookup(const char *name, u32 type, u32 mask);
struct crypto_alg *crypto_alg_mod_lookup(const char *name, u32 type, u32 mask);
int crypto_init_cipher_ops(struct crypto_tfm *tfm);
int crypto_init_compress_ops(struct crypto_tfm *tfm);
struct crypto_larval *crypto_larval_alloc(const char *name, u32 type, u32 mask);
void crypto_larval_kill(struct crypto_alg *alg);
void crypto_alg_tested(const char *name, int err);
void crypto_remove_spawns(struct crypto_alg *alg, struct list_head *list,
struct crypto_alg *nalg);
void crypto_remove_final(struct list_head *list);
void crypto_shoot_alg(struct crypto_alg *alg);
struct crypto_tfm *__crypto_alloc_tfm(struct crypto_alg *alg, u32 type,
u32 mask);
void *crypto_create_tfm(struct crypto_alg *alg,
const struct crypto_type *frontend);
struct crypto_alg *crypto_find_alg(const char *alg_name,
const struct crypto_type *frontend,
u32 type, u32 mask);
void *crypto_alloc_tfm(const char *alg_name,
const struct crypto_type *frontend, u32 type, u32 mask);
int crypto_register_notifier(struct notifier_block *nb);
int crypto_unregister_notifier(struct notifier_block *nb);
int crypto_probing_notify(unsigned long val, void *v);
unsigned int crypto_alg_extsize(struct crypto_alg *alg);
int crypto_type_has_alg(const char *name, const struct crypto_type *frontend,
u32 type, u32 mask);
static inline struct crypto_alg *crypto_alg_get(struct crypto_alg *alg)
{
refcount_inc(&alg->cra_refcnt);
return alg;
}
static inline void crypto_alg_put(struct crypto_alg *alg)
{
if (refcount_dec_and_test(&alg->cra_refcnt) && alg->cra_destroy)
alg->cra_destroy(alg);
}
static inline int crypto_tmpl_get(struct crypto_template *tmpl)
{
return try_module_get(tmpl->module);
}
static inline void crypto_tmpl_put(struct crypto_template *tmpl)
{
module_put(tmpl->module);
}
static inline int crypto_is_larval(struct crypto_alg *alg)
{
return alg->cra_flags & CRYPTO_ALG_LARVAL;
}
static inline int crypto_is_dead(struct crypto_alg *alg)
{
return alg->cra_flags & CRYPTO_ALG_DEAD;
}
static inline int crypto_is_moribund(struct crypto_alg *alg)
{
return alg->cra_flags & (CRYPTO_ALG_DEAD | CRYPTO_ALG_DYING);
}
static inline void crypto_notify(unsigned long val, void *v)
{
blocking_notifier_call_chain(&crypto_chain, val, v);
}
#endif /* _CRYPTO_INTERNAL_H */
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