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authorAl Viro <viro@zeniv.linux.org.uk>2020-03-03 18:14:30 +0300
committerAl Viro <viro@zeniv.linux.org.uk>2020-04-02 08:09:23 +0300
commit84f0cd9e83daa9a9c3e640f6d108e7e86edf0d86 (patch)
treee6fd9409c4c43ef6731809e98bb5b46230851ce3 /fs/namei.c
parent19f6028a01469276abe520c46a2c0ed0204e28d7 (diff)
downloadlinux-84f0cd9e83daa9a9c3e640f6d108e7e86edf0d86.tar.xz
pick_link(): pass it struct path already with normal refcounting rules
step_into() tries to avoid grabbing and dropping mount references on the steps that do not involve crossing mountpoints (which is obviously the majority of cases). So it uses a local struct path with unusual refcounting rules - path.mnt is pinned if and only if it's not equal to nd->path.mnt. We used to have similar beasts all over the place and we had quite a few bugs crop up in their handling - it's easy to get confused when changing e.g. cleanup on failure exits (or adding a new check, etc.) Now that's mostly gone - the step_into() instance (which is what we need them for) is the only one left. It is exposed to mount traversal and it's (shortly) seen by pick_link(). Since pick_link() needs to store it in link stack, where the normal rules apply, it has to make sure that mount is pinned regardless of nd->path.mnt value. That's done on all calls of pick_link() and very early in those. Let's do that in the caller (step_into()) instead - that way the fewer places need to be aware of such struct path instances. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs/namei.c')
-rw-r--r--fs/namei.c12
1 files changed, 6 insertions, 6 deletions
diff --git a/fs/namei.c b/fs/namei.c
index 1f092f9e321b..aab4eee6d56a 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1602,13 +1602,10 @@ static const char *pick_link(struct nameidata *nd, struct path *link,
int error;
if (unlikely(nd->total_link_count++ >= MAXSYMLINKS)) {
- path_to_nameidata(link, nd);
+ if (!(nd->flags & LOOKUP_RCU))
+ path_put(link);
return ERR_PTR(-ELOOP);
}
- if (!(nd->flags & LOOKUP_RCU)) {
- if (link->mnt == nd->path.mnt)
- mntget(link->mnt);
- }
error = nd_alloc_stack(nd);
if (unlikely(error)) {
if (error == -ECHILD) {
@@ -1713,10 +1710,13 @@ static const char *step_into(struct nameidata *nd, int flags,
nd->seq = seq;
return NULL;
}
- /* make sure that d_is_symlink above matches inode */
if (nd->flags & LOOKUP_RCU) {
+ /* make sure that d_is_symlink above matches inode */
if (read_seqcount_retry(&path.dentry->d_seq, seq))
return ERR_PTR(-ECHILD);
+ } else {
+ if (path.mnt == nd->path.mnt)
+ mntget(path.mnt);
}
return pick_link(nd, &path, inode, seq, flags);
}