Re: [PATCH v2 3/7] ceph: do not dencrypt the dentry name twice for readdir

[Jeff Layton <jlayton@kernel.org>]

On Tue, 2022-03-01 at 22:05 +0800, Xiubo Li wrote:
> On 3/1/22 9:31 PM, Jeff Layton wrote:
> > On Tue, 2022-03-01 at 19:30 +0800, xiubli@redhat.com wrote:
> > > From: Xiubo Li <xiubli@redhat.com>
> > > 
> > > Signed-off-by: Xiubo Li <xiubli@redhat.com>
> > > ---
> > >   fs/ceph/dir.c        | 66 +++++++++++++++++++++-----------------------
> > >   fs/ceph/inode.c      | 15 ++++++++++
> > >   fs/ceph/mds_client.h |  1 +
> > >   3 files changed, 47 insertions(+), 35 deletions(-)
> > > 
> > > diff --git a/fs/ceph/dir.c b/fs/ceph/dir.c
> > > index 6be0c1f793c2..e3917b4426e8 100644
> > > --- a/fs/ceph/dir.c
> > > +++ b/fs/ceph/dir.c
> > > @@ -316,8 +316,7 @@ static int ceph_readdir(struct file *file, struct dir_context *ctx)
> > >   	int err;
> > >   	unsigned frag = -1;
> > >   	struct ceph_mds_reply_info_parsed *rinfo;
> > > -	struct fscrypt_str tname = FSTR_INIT(NULL, 0);
> > > -	struct fscrypt_str oname = FSTR_INIT(NULL, 0);
> > > +	char *dentry_name = NULL;
> > >   
> > >   	dout("readdir %p file %p pos %llx\n", inode, file, ctx->pos);
> > >   	if (dfi->file_info.flags & CEPH_F_ATEND)
> > > @@ -345,10 +344,6 @@ static int ceph_readdir(struct file *file, struct dir_context *ctx)
> > >   		ctx->pos = 2;
> > >   	}
> > >   
> > > -	err = fscrypt_prepare_readdir(inode);
> > > -	if (err)
> > > -		goto out;
> > > -
> > 
> > Why are you removing this? This is what ensures that the key is loaded
> > if we're going to need it.
> 
> Since the dentry names are already decrypted in 
> ceph_readdir_prepopulate(), and this patch is trying to avoid do the 
> same thing again here after that.
> 
> Because in ceph_readdir() this isn't needed any more. And in other 
> places such as build path it will do it when needed.
> 
> > 
> > >   	spin_lock(&ci->i_ceph_lock);
> > >   	/* request Fx cap. if have Fx, we don't need to release Fs cap
> > >   	 * for later create/unlink. */
> > > @@ -369,14 +364,6 @@ static int ceph_readdir(struct file *file, struct dir_context *ctx)
> > >   		spin_unlock(&ci->i_ceph_lock);
> > >   	}
> > >   
> > > -	err = ceph_fname_alloc_buffer(inode, &tname);
> > > -	if (err < 0)
> > > -		goto out;
> > > -
> > > -	err = ceph_fname_alloc_buffer(inode, &oname);
> > > -	if (err < 0)
> > > -		goto out;
> > > -
> > >   	/* proceed with a normal readdir */
> > >   more:
> > >   	/* do we have the correct frag content buffered? */
> > > @@ -525,40 +512,49 @@ static int ceph_readdir(struct file *file, struct dir_context *ctx)
> > >   			}
> > >   		}
> > >   	}
> > > +
> > > +	dentry_name = kmalloc(280, GFP_KERNEL);
> > > +	if (!dentry_name) {
> > > +		err = -ENOMEM;
> > > +		goto out;
> > > +	}
> > > +
> > Woah, what's up with the bare "280" here?
> 
> The long snap name in format of "_${ENCRYPTED-SNAP-NAME}_${INO}", the 
> max length will be 1 +256 + 16.
> 

Ok. Best to make a named constant definition for this then. Bare numbers
in an allocation like this make it hard to understand what's going on.

> 
> > 
> > 
> > >   	for (; i < rinfo->dir_nr; i++) {
> > >   		struct ceph_mds_reply_dir_entry *rde = rinfo->dir_entries + i;
> > > -		struct ceph_fname fname = { .dir	= inode,
> > > -					    .name	= rde->name,
> > > -					    .name_len	= rde->name_len,
> > > -					    .ctext	= rde->altname,
> > > -					    .ctext_len	= rde->altname_len };
> > > -		u32 olen = oname.len;
> > > -
> > > -		err = ceph_fname_to_usr(&fname, &tname, &oname, NULL);
> > > -		if (err) {
> > > -			pr_err("%s unable to decode %.*s, got %d\n", __func__,
> > > -			       rde->name_len, rde->name, err);
> > > -			goto out;
> > > -		}
> > I may be missing something, but if you rip this out, where does the
> > decryption happen?
> 
> In ceph_readdir_prepopulate(), and it will set the rde->dentry, and here 
> we can get the name from the dentry directly instead of decrypt it again.
> 
> > 
> > > +		struct dentry *dn = rde->dentry;
> > > +		int name_len;
> > >   
> > >   		BUG_ON(rde->offset < ctx->pos);
> > >   		BUG_ON(!rde->inode.in);
> > > +		BUG_ON(!rde->dentry);
> > >   
> > >   		ctx->pos = rde->offset;
> > > -		dout("readdir (%d/%d) -> %llx '%.*s' %p\n",
> > > -		     i, rinfo->dir_nr, ctx->pos,
> > > -		     rde->name_len, rde->name, &rde->inode.in);
> > >   
> > > -		if (!dir_emit(ctx, oname.name, oname.len,
> > > +		spin_lock(&dn->d_lock);
> > > +		memcpy(dentry_name, dn->d_name.name, dn->d_name.len);
> > > +		name_len = dn->d_name.len;
> > > +		spin_unlock(&dn->d_lock);
> > > +
> > > +		dentry_name[name_len] = '\0';
> > > +		dout("readdir (%d/%d) -> %llx '%s' %p\n",
> > > +		     i, rinfo->dir_nr, ctx->pos, dentry_name, &rde->inode.in);
> > > +
> > > +		dput(dn);
> > > +		rde->dentry = NULL;
> > > +
> > > +		if (!dir_emit(ctx, dentry_name, name_len,
> > >   			      ceph_present_ino(inode->i_sb, le64_to_cpu(rde->inode.in->ino)),
> > >   			      le32_to_cpu(rde->inode.in->mode) >> 12)) {
> > >   			dout("filldir stopping us...\n");
> > >   			err = 0;
> > > +			for (; i < rinfo->dir_nr; i++) {
> > > +				rde = rinfo->dir_entries + i;
> > > +				dput(rde->dentry);
> > > +				rde->dentry = NULL;
> > > +			}
> > >   			goto out;
> > >   		}
> > >   
> > > -		/* Reset the lengths to their original allocated vals */
> > > -		oname.len = olen;
> > >   		ctx->pos++;
> > >   	}
> > >   
> > > @@ -616,8 +612,8 @@ static int ceph_readdir(struct file *file, struct dir_context *ctx)
> > >   	err = 0;
> > >   	dout("readdir %p file %p done.\n", inode, file);
> > >   out:
> > > -	ceph_fname_free_buffer(inode, &tname);
> > > -	ceph_fname_free_buffer(inode, &oname);
> > > +	if (dentry_name)
> > > +		kfree(dentry_name);
> > >   	return err;
> > >   }
> > >   
> > > diff --git a/fs/ceph/inode.c b/fs/ceph/inode.c
> > > index 2bc2f02b84e8..877e699fe43b 100644
> > > --- a/fs/ceph/inode.c
> > > +++ b/fs/ceph/inode.c
> > > @@ -1903,6 +1903,7 @@ int ceph_readdir_prepopulate(struct ceph_mds_request *req,
> > >   			goto out;
> > >   		}
> > >   
> > > +		rde->dentry = NULL;
> > >   		dname.name = oname.name;
> > >   		dname.len = oname.len;
> > >   		dname.hash = full_name_hash(parent, dname.name, dname.len);
> > > @@ -1963,6 +1964,12 @@ int ceph_readdir_prepopulate(struct ceph_mds_request *req,
> > >   			goto retry_lookup;
> > >   		}
> > >   
> > > +		/*
> > > +		 * ceph_readdir will use the dentry to get the name
> > > +		 * to avoid doing the dencrypt again there.
> > > +		 */
> > > +		rde->dentry = dget(dn);
> > > +
> > >   		/* inode */
> > >   		if (d_really_is_positive(dn)) {
> > >   			in = d_inode(dn);
> > > @@ -2025,6 +2032,14 @@ int ceph_readdir_prepopulate(struct ceph_mds_request *req,
> > >   		dput(dn);
> > >   	}
> > >   out:
> > > +	if (err) {
> > > +		for (; i >= 0; i--) {
> > > +			struct ceph_mds_reply_dir_entry *rde;
> > > +
> > > +			rde = rinfo->dir_entries + i;
> > > +			dput(rde->dentry);
> > > +		}
> > > +	}
> > >   	if (err == 0 && skipped == 0) {
> > >   		set_bit(CEPH_MDS_R_DID_PREPOPULATE, &req->r_req_flags);
> > >   		req->r_readdir_cache_idx = cache_ctl.index;
> > > diff --git a/fs/ceph/mds_client.h b/fs/ceph/mds_client.h
> > > index 0dfe24f94567..663d7754d57d 100644
> > > --- a/fs/ceph/mds_client.h
> > > +++ b/fs/ceph/mds_client.h
> > > @@ -96,6 +96,7 @@ struct ceph_mds_reply_info_in {
> > >   };
> > >   
> > >   struct ceph_mds_reply_dir_entry {
> > > +	struct dentry		      *dentry;
> > >   	char                          *name;
> > >   	u8			      *altname;
> > >   	u32                           name_len;
> > 
> > NAK on this patch as it is...
> > 
> 

-- 
Jeff Layton <jlayton@kernel.org>