On Sat, Oct 11, 2014 at 05:58:08PM -0500, Eric Biggers wrote:
> In path_init(), said commit added a call to read_seqcount_retry() after
> loading
> the inode. I see two problems with this:
>
> - The read_seqcount_retry() isn't needed just to load the inode pointer, so
> the change doesn't seem to accomplish anything.
Huh? What's to guarantee that dentry hasn't become negative since the
moment we'd fetched the seqcount? _That_ is the problem we are dealing
with here - link_path_walk() relies on nd->inode being non-NULL.
> - If the -ECHILD code path actually runs, the reference to the 'struct file'
> can be leaked.
Umm... That, OTOH, might be true, _if_ we could hit it on the path where
nd->path comes from file (and descriptor table had been shared). Which
could happen, if we could get d_drop() done to that sucker for some
reason - other codepaths bumping the seqcount are impossible for pinned
dentry (including that of an opened file).
Which can, indeed, happen on something like NFS. OK, so all callers of
path_init() should go to the same place where they go on link_path_walk()
failure, like this. And that's probably what we want in backports; however,
longer term we would be better off with a combined path_init + link_path_walk -
all callers do exactly the same thing there... OK, that can be in a followup...
Signed-off-by: Al Viro <v...@zeniv.linux.org.uk>
---
diff --git a/fs/namei.c b/fs/namei.c
index d20d579..0f64aa4 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1950,7 +1950,7 @@ static int path_lookupat(int dfd, const char *name,
err = path_init(dfd, name, flags | LOOKUP_PARENT, nd, &base);
if (unlikely(err))
- return err;
+ goto out;
current->total_link_count = 0;
err = link_path_walk(name, nd);
@@ -1982,6 +1982,7 @@ static int path_lookupat(int dfd, const char *name,
}
}
+out:
if (base)
fput(base);
@@ -2301,7 +2302,7 @@ path_mountpoint(int dfd, const char *name, struct path
*path, unsigned int flags
err = path_init(dfd, name, flags | LOOKUP_PARENT, &nd, &base);
if (unlikely(err))
- return err;
+ goto out;
current->total_link_count = 0;
err = link_path_walk(name, &nd);
--
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