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

[Xiubo Li <xiubli@redhat.com>]

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.


>
>
>>   	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...
>