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Message-ID: <166147984377.25420.5747334898411663007.stgit@noble.brown>
Date: Fri, 26 Aug 2022 12:10:43 +1000
From: NeilBrown <neilb@...e.de>
To: Al Viro <viro@...iv.linux.org.uk>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Daire Byrne <daire@...g.com>,
Trond Myklebust <trond.myklebust@...merspace.com>,
Chuck Lever <chuck.lever@...cle.com>
Cc: Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH 09/10] VFS: add LOOKUP_SILLY_RENAME
When performing a "silly rename" to avoid removing a file that is still
open, we need to perform a lookup in a directory that is already locked.
In order to allow common functions to be used for this lookup, introduce
LOOKUP_SILLY_RENAME which affirms that the directory is already locked
and that the vfsmnt is already writable.
When LOOKUP_SILLY_RENAME is set, path->mnt can be NULL. As
i_op->rename() doesn't make the vfsmnt available, this is unavoidable.
So we ensure that a NULL ->mnt isn't fatal.
Signed-off-by: NeilBrown <neilb@...e.de>
---
fs/dcache.c | 3 +-
fs/namei.c | 88 +++++++++++++++++++++++++++++--------------------
include/linux/namei.h | 9 +++--
3 files changed, 59 insertions(+), 41 deletions(-)
diff --git a/fs/dcache.c b/fs/dcache.c
index d6bfa49b143b..9bf346a9de52 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -3297,7 +3297,8 @@ EXPORT_SYMBOL(d_tmpfile);
* If the parent directory is locked with I_MUTEX_NORMAL, use I_MUTEX_NORMAL.
* If the parent is locked with I_MUTEX_PARENT, I_MUTEX_PARENT2 or
* I_MUTEX_CHILD, use I_MUTEX_PARENT or, for the second in a rename,
- * I_MUTEX_PARENT2.
+ * I_MUTEX_PARENT2. When a third name is needed, as with "silly-rename"
+ * I_MUTEX_CHILD is used.
*/
bool d_lock_update_nested(struct dentry *dentry,
struct dentry *base, const struct qstr *name,
diff --git a/fs/namei.c b/fs/namei.c
index ef994239fa7c..c9bbff120bf9 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1650,12 +1650,14 @@ static struct dentry *__lookup_hash(const struct qstr *name,
}
/*
- * Parent directory (base) is not locked. We take either an exclusive
- * or shared lock depending on the fs preference, then do a lookup,
- * and then set the DCACHE_PAR_UPDATE bit on the child if a shared lock
- * was taken on the parent.
+ * Without LOOKUP_SILLY_RENAME parent directory (base) is not locked.
+ * We take either an exclusive or shared lock depending on the fs
+ * preference, then do a lookup, and then set the DCACHE_PAR_UPDATE bit
+ * on the child if a shared lock was taken on the parent.
* If LOOKUP_EXCL, name should not already exist, else -EEXIST
* If not LOOKUP_CREATE, name should already exist, else -ENOENT
+ * If LOOKUP_SILLY_RENAME, don't require write access. In this case
+ * path->mnt may be NULL.
*/
static struct dentry *lookup_hash_update(
const struct qstr *name,
@@ -1665,21 +1667,26 @@ static struct dentry *lookup_hash_update(
struct dentry *dentry;
struct dentry *base = path->dentry;
struct inode *dir = base->d_inode;
- int err, err2;
-
- /* For create, don't fail immediately if it's r/o,
- * at least try to report other errors.
- * For unlink/rmdir where LOOKUP_REVAl is the only
- * flag, fail immediately if r/o.
- */
- err2 = mnt_want_write(path->mnt);
- if (err2 && (flags & ~LOOKUP_REVAL) == 0)
- return ERR_PTR(err2);
+ int err, err2 = 0;
+ int class;
+
+ if (!(flags & LOOKUP_SILLY_RENAME)) {
+ /* For create, don't fail immediately if it's r/o,
+ * at least try to report other errors.
+ * For unlink/rmdir where LOOKUP_REVAl is the only
+ * flag, fail immediately if r/o.
+ */
+ err2 = mnt_want_write(path->mnt);
+ if (err2 && (flags & ~LOOKUP_REVAL) == 0)
+ return ERR_PTR(err2);
- if (wq && IS_PAR_UPDATE(dir))
- inode_lock_shared_nested(dir, I_MUTEX_PARENT);
- else
- inode_lock_nested(dir, I_MUTEX_PARENT);
+ if (wq && IS_PAR_UPDATE(dir))
+ inode_lock_shared_nested(dir, I_MUTEX_PARENT);
+ else
+ inode_lock_nested(dir, I_MUTEX_PARENT);
+ class = I_MUTEX_PARENT;
+ } else
+ class = I_MUTEX_CHILD;
retry:
dentry = __lookup_hash(name, base, flags, wq);
@@ -1687,7 +1694,7 @@ static struct dentry *lookup_hash_update(
err = PTR_ERR(dentry);
goto out_err;
}
- if (!d_lock_update_nested(dentry, base, name, I_MUTEX_PARENT)) {
+ if (!d_lock_update_nested(dentry, base, name, class)) {
/*
* Failed to get lock due to race with unlink or rename
* - try again
@@ -1724,12 +1731,14 @@ static struct dentry *lookup_hash_update(
return dentry;
out_err:
- if (wq && IS_PAR_UPDATE(dir))
- inode_unlock_shared(dir);
- else
- inode_unlock(dir);
- if (!err2)
- mnt_drop_write(path->mnt);
+ if (!(flags & LOOKUP_SILLY_RENAME)) {
+ if (wq && IS_PAR_UPDATE(dir))
+ inode_unlock_shared(dir);
+ else
+ inode_unlock(dir);
+ if (!err2)
+ mnt_drop_write(path->mnt);
+ }
return ERR_PTR(err);
}
@@ -1751,18 +1760,22 @@ struct dentry *lookup_hash_update_len(const char *name, int nlen,
EXPORT_SYMBOL(lookup_hash_update_len);
void __done_path_update(struct path *path, struct dentry *dentry,
- bool with_wq)
+ bool with_wq, unsigned int flags)
{
struct inode *dir = path->dentry->d_inode;
d_lookup_done(dentry);
d_unlock_update(dentry);
- if (IS_PAR_UPDATE(dir) && with_wq)
- inode_unlock_shared(dir);
- else
- inode_unlock(dir);
- dput(dentry);
- mnt_drop_write(path->mnt);
+ if (flags & LOOKUP_SILLY_RENAME) {
+ dput(dentry);
+ } else {
+ if (IS_PAR_UPDATE(dir) && with_wq)
+ inode_unlock_shared(dir);
+ else
+ inode_unlock(dir);
+ dput(dentry);
+ mnt_drop_write(path->mnt);
+ }
}
EXPORT_SYMBOL(__done_path_update);
@@ -4122,7 +4135,8 @@ static struct dentry *filename_create_one(struct qstr *last, struct path *path,
wait_queue_head_t *wq)
{
bool want_dir = lookup_flags & LOOKUP_DIRECTORY;
- unsigned int reval_flag = lookup_flags & LOOKUP_REVAL;
+ unsigned int flags = lookup_flags & (LOOKUP_REVAL |
+ LOOKUP_SILLY_RENAME);
unsigned int create_flag = LOOKUP_CREATE;
/*
@@ -4136,7 +4150,7 @@ static struct dentry *filename_create_one(struct qstr *last, struct path *path,
*/
create_flag = 0;
return lookup_hash_update(last, path,
- reval_flag | create_flag | LOOKUP_EXCL,
+ flags | create_flag | LOOKUP_EXCL,
wq);
}
@@ -4146,10 +4160,12 @@ struct dentry *filename_create_one_len(const char *name, int nlen,
wait_queue_head_t *wq)
{
struct qstr this;
+ struct user_namespace *uns = &init_user_ns;
int err;
- err = lookup_one_common(mnt_user_ns(path->mnt), name,
- path->dentry, nlen, &this);
+ if (path->mnt)
+ uns = mnt_user_ns(path->mnt);
+ err = lookup_one_common(uns, name, path->dentry, nlen, &this);
if (err)
return ERR_PTR(err);
return filename_create_one(&this, path, lookup_flags, wq);
diff --git a/include/linux/namei.h b/include/linux/namei.h
index 29756921f69b..92a62b04a83d 100644
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -21,6 +21,7 @@ enum {LAST_NORM, LAST_ROOT, LAST_DOT, LAST_DOTDOT};
#define LOOKUP_FOLLOW 0x0001 /* follow links at the end */
#define LOOKUP_DIRECTORY 0x0002 /* require a directory */
#define LOOKUP_AUTOMOUNT 0x0004 /* force terminal automount */
+#define LOOKUP_SILLY_RENAME 0x0008 /* Directory already locked, don't lock again */
#define LOOKUP_EMPTY 0x4000 /* accept empty path [user_... only] */
#define LOOKUP_DOWN 0x8000 /* follow mounts in the starting point */
#define LOOKUP_MOUNTPOINT 0x0080 /* follow mounts in the end */
@@ -64,20 +65,20 @@ extern struct dentry *user_path_create(int, const char __user *, struct path *,
extern struct dentry *lookup_hash_update_len(const char *name, int nlen,
struct path *path, unsigned int flags,
wait_queue_head_t *wq);
-extern void __done_path_update(struct path *, struct dentry *, bool);
+extern void __done_path_update(struct path *, struct dentry *, bool, unsigned int);
static inline void done_path_update(struct path *path, struct dentry *dentry)
{
- __done_path_update(path, dentry, true);
+ __done_path_update(path, dentry, true, 0);
}
static inline void done_path_create(struct path *path, struct dentry *dentry)
{
- __done_path_update(path, dentry, false);
+ __done_path_update(path, dentry, false, 0);
path_put(path);
}
static inline void done_path_create_wq(struct path *path, struct dentry *dentry,
bool with_wq)
{
- __done_path_update(path, dentry, with_wq);
+ __done_path_update(path, dentry, with_wq, 0);
path_put(path);
}
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