[PATCH 2/4] take LOOKUP_{ROOT,ROOT_GRABBED,JUMPED} out of LOOKUP_... space

From: Al Viro
Date: Tue Jun 08 2021 - 07:39:36 EST

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Separate field in nameidata (nd->state) holding the flags that
should be internal-only - that way we both get some spare bits
in LOOKUP_... and get simpler rules for nd->root lifetime rules,
since we can set the replacement of LOOKUP_ROOT (ND_ROOT_PRESET)
at the same time we set nd->root.

Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
---
Documentation/filesystems/path-lookup.rst | 6 ++--
fs/namei.c | 54 ++++++++++++++++++-------------
fs/nfs/nfstrace.h | 4 ---
include/linux/namei.h | 3 --
4 files changed, 34 insertions(+), 33 deletions(-)

diff --git a/Documentation/filesystems/path-lookup.rst b/Documentation/filesystems/path-lookup.rst
index c482e1619e77..ede67f705787 100644
--- a/Documentation/filesystems/path-lookup.rst
+++ b/Documentation/filesystems/path-lookup.rst
@@ -1321,18 +1321,18 @@ to lookup: RCU-walk, REF-walk, and REF-walk with forced revalidation.
yet. This is primarily used to tell the audit subsystem the full
context of a particular access being audited.

-``LOOKUP_ROOT`` indicates that the ``root`` field in the ``nameidata`` was
+``ND_ROOT_PRESET`` indicates that the ``root`` field in the ``nameidata`` was
provided by the caller, so it shouldn't be released when it is no
longer needed.

-``LOOKUP_JUMPED`` means that the current dentry was chosen not because
+``ND_JUMPED`` means that the current dentry was chosen not because
it had the right name but for some other reason. This happens when
following "``..``", following a symlink to ``/``, crossing a mount point
or accessing a "``/proc/$PID/fd/$FD``" symlink (also known as a "magic
link"). In this case the filesystem has not been asked to revalidate the
name (with ``d_revalidate()``). In such cases the inode may still need
to be revalidated, so ``d_op->d_weak_revalidate()`` is called if
-``LOOKUP_JUMPED`` is set when the look completes - which may be at the
+``ND_JUMPED`` is set when the look completes - which may be at the
final component or, when creating, unlinking, or renaming, at the penultimate component.

Resolution-restriction flags
diff --git a/fs/namei.c b/fs/namei.c
index 4b6cf4974dd7..622b9f15bf1c 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -554,7 +554,7 @@ struct nameidata {
struct qstr last;
struct path root;
struct inode *inode; /* path.dentry.d_inode */
- unsigned int flags;
+ unsigned int flags, state;
unsigned seq, m_seq, r_seq;
int last_type;
unsigned depth;
@@ -573,6 +573,10 @@ struct nameidata {
umode_t dir_mode;
} __randomize_layout;

+#define ND_ROOT_PRESET 1
+#define ND_ROOT_GRABBED 2
+#define ND_JUMPED 4
+
static void set_nameidata(struct nameidata *p, int dfd, struct filename *name)
{
struct nameidata *old = current->nameidata;
@@ -583,6 +587,7 @@ static void set_nameidata(struct nameidata *p, int dfd, struct filename *name)
p->path.dentry = NULL;
p->total_link_count = old ? old->total_link_count : 0;
p->saved = old;
+ p->state = 0;
current->nameidata = p;
}

@@ -645,9 +650,9 @@ static void terminate_walk(struct nameidata *nd)
path_put(&nd->path);
for (i = 0; i < nd->depth; i++)
path_put(&nd->stack[i].link);
- if (nd->flags & LOOKUP_ROOT_GRABBED) {
+ if (nd->state & ND_ROOT_GRABBED) {
path_put(&nd->root);
- nd->flags &= ~LOOKUP_ROOT_GRABBED;
+ nd->state &= ~ND_ROOT_GRABBED;
}
} else {
nd->flags &= ~LOOKUP_RCU;
@@ -710,9 +715,9 @@ static bool legitimize_root(struct nameidata *nd)
if (!nd->root.mnt && (nd->flags & LOOKUP_IS_SCOPED))
return false;
/* Nothing to do if nd->root is zero or is managed by the VFS user. */
- if (!nd->root.mnt || (nd->flags & LOOKUP_ROOT))
+ if (!nd->root.mnt || (nd->state & ND_ROOT_PRESET))
return true;
- nd->flags |= LOOKUP_ROOT_GRABBED;
+ nd->state |= ND_ROOT_GRABBED;
return legitimize_path(nd, &nd->root, nd->root_seq);
}

@@ -849,8 +854,9 @@ static int complete_walk(struct nameidata *nd)
* We don't want to zero nd->root for scoped-lookups or
* externally-managed nd->root.
*/
- if (!(nd->flags & (LOOKUP_ROOT | LOOKUP_IS_SCOPED)))
- nd->root.mnt = NULL;
+ if (!(nd->state & ND_ROOT_PRESET))
+ if (!(nd->flags & LOOKUP_IS_SCOPED))
+ nd->root.mnt = NULL;
nd->flags &= ~LOOKUP_CACHED;
if (!try_to_unlazy(nd))
return -ECHILD;
@@ -877,7 +883,7 @@ static int complete_walk(struct nameidata *nd)
return -EXDEV;
}

- if (likely(!(nd->flags & LOOKUP_JUMPED)))
+ if (likely(!(nd->state & ND_JUMPED)))
return 0;

if (likely(!(dentry->d_flags & DCACHE_OP_WEAK_REVALIDATE)))
@@ -915,7 +921,7 @@ static int set_root(struct nameidata *nd)
} while (read_seqcount_retry(&fs->seq, seq));
} else {
get_fs_root(fs, &nd->root);
- nd->flags |= LOOKUP_ROOT_GRABBED;
+ nd->state |= ND_ROOT_GRABBED;
}
return 0;
}
@@ -948,7 +954,7 @@ static int nd_jump_root(struct nameidata *nd)
path_get(&nd->path);
nd->inode = nd->path.dentry->d_inode;
}
- nd->flags |= LOOKUP_JUMPED;
+ nd->state |= ND_JUMPED;
return 0;
}

@@ -976,7 +982,7 @@ int nd_jump_link(struct path *path)
path_put(&nd->path);
nd->path = *path;
nd->inode = nd->path.dentry->d_inode;
- nd->flags |= LOOKUP_JUMPED;
+ nd->state |= ND_JUMPED;
return 0;

err:
@@ -1424,7 +1430,7 @@ static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
if (mounted) {
path->mnt = &mounted->mnt;
dentry = path->dentry = mounted->mnt.mnt_root;
- nd->flags |= LOOKUP_JUMPED;
+ nd->state |= ND_JUMPED;
*seqp = read_seqcount_begin(&dentry->d_seq);
*inode = dentry->d_inode;
/*
@@ -1469,7 +1475,7 @@ static inline int handle_mounts(struct nameidata *nd, struct dentry *dentry,
if (unlikely(nd->flags & LOOKUP_NO_XDEV))
ret = -EXDEV;
else
- nd->flags |= LOOKUP_JUMPED;
+ nd->state |= ND_JUMPED;
}
if (unlikely(ret)) {
dput(path->dentry);
@@ -2220,7 +2226,7 @@ static int link_path_walk(const char *name, struct nameidata *nd)
case 2:
if (name[1] == '.') {
type = LAST_DOTDOT;
- nd->flags |= LOOKUP_JUMPED;
+ nd->state |= ND_JUMPED;
}
break;
case 1:
@@ -2228,7 +2234,7 @@ static int link_path_walk(const char *name, struct nameidata *nd)
}
if (likely(type == LAST_NORM)) {
struct dentry *parent = nd->path.dentry;
- nd->flags &= ~LOOKUP_JUMPED;
+ nd->state &= ~ND_JUMPED;
if (unlikely(parent->d_flags & DCACHE_OP_HASH)) {
struct qstr this = { { .hash_len = hash_len }, .name = name };
err = parent->d_op->d_hash(parent, &this);
@@ -2302,14 +2308,15 @@ static const char *path_init(struct nameidata *nd, unsigned flags)
if (flags & LOOKUP_RCU)
rcu_read_lock();

- nd->flags = flags | LOOKUP_JUMPED;
+ nd->flags = flags;
+ nd->state |= ND_JUMPED;
nd->depth = 0;

nd->m_seq = __read_seqcount_begin(&mount_lock.seqcount);
nd->r_seq = __read_seqcount_begin(&rename_lock.seqcount);
smp_rmb();

- if (flags & LOOKUP_ROOT) {
+ if (nd->state & ND_ROOT_PRESET) {
struct dentry *root = nd->root.dentry;
struct inode *inode = root->d_inode;
if (*s && unlikely(!d_can_lookup(root)))
@@ -2384,7 +2391,7 @@ static const char *path_init(struct nameidata *nd, unsigned flags)
nd->root_seq = nd->seq;
} else {
path_get(&nd->root);
- nd->flags |= LOOKUP_ROOT_GRABBED;
+ nd->state |= ND_ROOT_GRABBED;
}
}
return s;
@@ -2423,7 +2430,7 @@ static int path_lookupat(struct nameidata *nd, unsigned flags, struct path *path
;
if (!err && unlikely(nd->flags & LOOKUP_MOUNTPOINT)) {
err = handle_lookup_down(nd);
- nd->flags &= ~LOOKUP_JUMPED; // no d_weak_revalidate(), please...
+ nd->state &= ~ND_JUMPED; // no d_weak_revalidate(), please...
}
if (!err)
err = complete_walk(nd);
@@ -2447,11 +2454,11 @@ int filename_lookup(int dfd, struct filename *name, unsigned flags,
struct nameidata nd;
if (IS_ERR(name))
return PTR_ERR(name);
+ set_nameidata(&nd, dfd, name);
if (unlikely(root)) {
nd.root = *root;
- flags |= LOOKUP_ROOT;
+ nd.state = ND_ROOT_PRESET;
}
- set_nameidata(&nd, dfd, name);
retval = path_lookupat(&nd, flags | LOOKUP_RCU, path);
if (unlikely(retval == -ECHILD))
retval = path_lookupat(&nd, flags, path);
@@ -3539,7 +3546,7 @@ struct file *do_file_open_root(const struct path *root,
struct nameidata nd;
struct file *file;
struct filename *filename;
- int flags = op->lookup_flags | LOOKUP_ROOT;
+ int flags = op->lookup_flags;

if (d_is_symlink(root->dentry) && op->intent & LOOKUP_OPEN)
return ERR_PTR(-ELOOP);
@@ -3548,8 +3555,9 @@ struct file *do_file_open_root(const struct path *root,
if (IS_ERR(filename))
return ERR_CAST(filename);

- nd.root = *root;
set_nameidata(&nd, -1, filename);
+ nd.root = *root;
+ nd.state = ND_ROOT_PRESET;
file = path_openat(&nd, op, flags | LOOKUP_RCU);
if (unlikely(file == ERR_PTR(-ECHILD)))
file = path_openat(&nd, op, flags);
diff --git a/fs/nfs/nfstrace.h b/fs/nfs/nfstrace.h
index 5a59dcdce0b2..cb7f49723bbf 100644
--- a/fs/nfs/nfstrace.h
+++ b/fs/nfs/nfstrace.h
@@ -271,8 +271,6 @@ TRACE_DEFINE_ENUM(LOOKUP_OPEN);
TRACE_DEFINE_ENUM(LOOKUP_CREATE);
TRACE_DEFINE_ENUM(LOOKUP_EXCL);
TRACE_DEFINE_ENUM(LOOKUP_RENAME_TARGET);
-TRACE_DEFINE_ENUM(LOOKUP_JUMPED);
-TRACE_DEFINE_ENUM(LOOKUP_ROOT);
TRACE_DEFINE_ENUM(LOOKUP_EMPTY);
TRACE_DEFINE_ENUM(LOOKUP_DOWN);

@@ -288,8 +286,6 @@ TRACE_DEFINE_ENUM(LOOKUP_DOWN);
{ LOOKUP_CREATE, "CREATE" }, \
{ LOOKUP_EXCL, "EXCL" }, \
{ LOOKUP_RENAME_TARGET, "RENAME_TARGET" }, \
- { LOOKUP_JUMPED, "JUMPED" }, \
- { LOOKUP_ROOT, "ROOT" }, \
{ LOOKUP_EMPTY, "EMPTY" }, \
{ LOOKUP_DOWN, "DOWN" })

diff --git a/include/linux/namei.h b/include/linux/namei.h
index b9605b2b46e7..be9a2b349ca7 100644
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -36,9 +36,6 @@ enum {LAST_NORM, LAST_ROOT, LAST_DOT, LAST_DOTDOT};

/* internal use only */
#define LOOKUP_PARENT 0x0010
-#define LOOKUP_JUMPED 0x1000
-#define LOOKUP_ROOT 0x2000
-#define LOOKUP_ROOT_GRABBED 0x0008

/* Scoping flags for lookup. */
#define LOOKUP_NO_SYMLINKS 0x010000 /* No symlink crossing. */
--
2.11.0

Next message: Al Viro: "[PATCH 1/4] switch file_open_root() to struct path"
Previous message: Al Viro: "[PATCH 3/4] teach set_nameidata() to handle setting the root as well"
In reply to: Al Viro: "[PATCH 3/4] teach set_nameidata() to handle setting the root as well"
Next in thread: Christian Brauner: "Re: [PATCHES] namei cleanups"
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