[PATCH RFC v8 04/10] namei: split out nd->dfd handling to dirfd_path_init

Aleksa Sarai
2019-05-20T13:32:59Z

Previously, path_init's handling of *at(dfd, ...) was only done once,
but with LOOKUP_BENEATH (and LOOKUP_IN_ROOT) we have to parse the
initial nd->path at different times (before or after absolute path
handling) depending on whether we have been asked to scope resolution
within a root.

Signed-off-by: Aleksa Sarai <cyphar at cyphar.com>
---
fs/namei.c | 103 ++++++++++++++++++++++++++++++-----------------------
1 file changed, 59 insertions(+), 44 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 46c5302eea4a..dc323e25d4d2 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2251,9 +2251,59 @@ static int link_path_walk(const char *name, struct nameidata *nd)
}
}

+/*
+ * Configure nd->path based on the nd->dfd. This is only used as part of
+ * path_init().
+ */
+static inline int dirfd_path_init(struct nameidata *nd)
+{
+ if (nd->dfd == AT_FDCWD) {
+ if (nd->flags & LOOKUP_RCU) {
+ struct fs_struct *fs = current->fs;
+ unsigned seq;
+
+ do {
+ seq = read_seqcount_begin(&fs->seq);
+ nd->path = fs->pwd;
+ nd->inode = nd->path.dentry->d_inode;
+ nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq);
+ } while (read_seqcount_retry(&fs->seq, seq));
+ } else {
+ get_fs_pwd(current->fs, &nd->path);
+ nd->inode = nd->path.dentry->d_inode;
+ }
+ } else {
+ /* Caller must check execute permissions on the starting path component */
+ struct fd f = fdget_raw(nd->dfd);
+ struct dentry *dentry;
+
+ if (!f.file)
+ return -EBADF;
+
+ dentry = f.file->f_path.dentry;
+
+ if (*nd->name->name && unlikely(!d_can_lookup(dentry))) {
+ fdput(f);
+ return -ENOTDIR;
+ }
+
+ nd->path = f.file->f_path;
+ if (nd->flags & LOOKUP_RCU) {
+ nd->inode = nd->path.dentry->d_inode;
+ nd->seq = read_seqcount_begin(&nd->path.dentry->d_seq);
+ } else {
+ path_get(&nd->path);
+ nd->inode = nd->path.dentry->d_inode;
+ }
+ fdput(f);
+ }
+ return 0;
+}
+
/* must be paired with terminate_walk() */
static const char *path_init(struct nameidata *nd, unsigned flags)
{
+ int error;
const char *s = nd->name->name;

if (!*s)
@@ -2287,52 +2337,17 @@ static const char *path_init(struct nameidata *nd, unsigned flags)

nd->m_seq = read_seqbegin(&mount_lock);
if (*s == '/') {
- set_root(nd);
- if (likely(!nd_jump_root(nd)))
- return s;
- return ERR_PTR(-ECHILD);
- } else if (nd->dfd == AT_FDCWD) {
- if (flags & LOOKUP_RCU) {
- struct fs_struct *fs = current->fs;
- unsigned seq;
-
- do {
- seq = read_seqcount_begin(&fs->seq);
- nd->path = fs->pwd;
- nd->inode = nd->path.dentry->d_inode;
- nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq);
- } while (read_seqcount_retry(&fs->seq, seq));
- } else {
- get_fs_pwd(current->fs, &nd->path);
- nd->inode = nd->path.dentry->d_inode;
- }
- return s;
- } else {
- /* Caller must check execute permissions on the starting path component */
- struct fd f = fdget_raw(nd->dfd);
- struct dentry *dentry;
-
- if (!f.file)
- return ERR_PTR(-EBADF);
-
- dentry = f.file->f_path.dentry;
-
- if (*s && unlikely(!d_can_lookup(dentry))) {
- fdput(f);
- return ERR_PTR(-ENOTDIR);
- }
-
- nd->path = f.file->f_path;
- if (flags & LOOKUP_RCU) {
- nd->inode = nd->path.dentry->d_inode;
- nd->seq = read_seqcount_begin(&nd->path.dentry->d_seq);
- } else {
- path_get(&nd->path);
- nd->inode = nd->path.dentry->d_inode;
- }
- fdput(f);
+ if (likely(!nd->root.mnt))
+ set_root(nd);
+ error = nd_jump_root(nd);
+ if (unlikely(error))
+ s = ERR_PTR(error);
return s;
}
+ error = dirfd_path_init(nd);
+ if (unlikely(error))
+ return ERR_PTR(error);
+ return s;
}

static const char *trailing_symlink(struct nameidata *nd)
--
2.21.0