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 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.

>  	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?


>  	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?

> +		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>