On Oct 15, 2018, at 19:29, Jeff Layton jlayton@redhat.com wrote:
On Mon, 2018-10-15 at 09:58 +0800, Yan, Zheng wrote:
On Oct 12, 2018, at 18:56, Jeff Layton jlayton@redhat.com wrote:
On Fri, 2018-10-12 at 10:39 +0800, Yan, Zheng wrote:
On Oct 11, 2018, at 22:49, Jeff Layton jlayton@redhat.com wrote:
On Fri, 2018-09-28 at 17:43 +0800, Yan, Zheng wrote:
This reverts commit 8b8f53af1ed9df88a4c0fbfdf3db58f62060edf3.
splice_dentry() is used by three places. For two places, req->r_dentry is passed to splice_dentry(). In the case of error, req->r_dentry does not get updated. So splice_dentry() should not drop reference.
Cc: stable@vger.kernel.org #4.18 Signed-off-by: "Yan, Zheng" zyan@redhat.com
fs/ceph/inode.c | 1 - 1 file changed, 1 deletion(-)
diff --git a/fs/ceph/inode.c b/fs/ceph/inode.c index c6bbb7aa99e4..375924b2bc86 100644 --- a/fs/ceph/inode.c +++ b/fs/ceph/inode.c @@ -1140,7 +1140,6 @@ static struct dentry *splice_dentry(struct dentry *dn, struct inode *in) if (IS_ERR(realdn)) { pr_err("splice_dentry error %ld %p inode %p ino %llx.%llx\n", PTR_ERR(realdn), dn, in, ceph_vinop(in));
dput(dn);This might be ok, buI have some real concerns about splice_dentry and its callers -- particularly ceph_fill_trace:
We hold a reference to dn on entry to splice_dentry. We then call d_splice_alias and get back an error, and now we don't put the old dentry.
Fine -- we have to then expect the caller to do it. Unfortunately, the callers in ceph_fill_trace do this:
dn = splice_dentry(dn, in); if (IS_ERR(dn)) { err = PTR_ERR(dn); goto done; } req->r_dentry = dn; /* may have spliced */The old value of dn gets clobbered once that comes back with an ERR_PTR. I guess we could claim that r_dentry will still be set to the old value at that point and that it would get cleaned up when it gets cleaned up.
But...I see this higher up in ceph_fill_trace at the end of the CEPH_MFS_OP_RENAME condition block:
dn = req->r_old_dentry; /* use old_dentry */So now I'm worried about the case where the splice succeeds. ISTM that "dn" can represent either r_dentry or r_old_dentry at the point where splice_dentry gets called, but we only ever reset the value of r_dentry there.
If dn == r_old_dentry at the time that splice_dentry is called, and then that succeeds, we'll end up leaking the reference to r_dentry and then doing an overput on r_old_dentry.
Good catch
I think it might help to establish clear "ownership" of the dentry references throughout that function. Consider zeroing out r_dentry and r_old_dentry at the time that you set the local variables? That might make this whole thing less fragile.
Before the function return, we need to set req->r_dentry again. This will introduce duplicated code because there are several ‘goto’ in the function. How about following change.
dn = req->r_old_dentry; /* use old_dentry */
/* swap r_dentry and r_old_dentry */req->r_dentry = req->r_old_dentry;req->r_old_dentry = dn;dn = req->r_dentry;Why do we need to reset r_dentry? I don't see where it gets used after ceph_fill_trace returns, so I gather we're just resetting it to clean up the references? Your proposed fix looks like it would fix that bug. It will mean that the values in the req will change but maybe that's ok.
It’s used by ceph_finish_lookup
In that case, it might be bad idea to overwrite the value of r_dentry with the r_old_dentry pointer?
ceph_finish_lookup() is not used in the rename case ;)
Rgeards Yan, Zheng
Another idea might be to just keep an extra reference to "dn", and not reset r_dentry and r_old_dentry? It's a bit more code, but it might be a cleaner fix, long-term.
I will check, Thanks
Yan, Zheng
-- Jeff Layton jlayton@redhat.com
-- Jeff Layton jlayton@redhat.com