Re: [PATCH v2 1/7] ceph: fail the request when failing to decode dentry names

[Xiubo Li <xiubli@xxxxxxxxxx>]

On 3/1/22 9:20 PM, Jeff Layton wrote:
> On Tue, 2022-03-01 at 19:30 +0800, xiubli@xxxxxxxxxx wrote:
> > From: Xiubo Li <xiubli@xxxxxxxxxx>
> >
> > ------------[ cut here ]------------
> > kernel BUG at fs/ceph/dir.c:537!
> > invalid opcode: 0000 [#1] PREEMPT SMP KASAN NOPTI
> > CPU: 16 PID: 21641 Comm: ls Tainted: G            E     5.17.0-rc2+ #92
> > Hardware name: Red Hat RHEV Hypervisor, BIOS 1.11.0-2.el7 04/01/2014
> >
> > The corresponding code in ceph_readdir() is:
> >
> > 	BUG_ON(rde->offset < ctx->pos);
> >
> > Signed-off-by: Xiubo Li <xiubli@xxxxxxxxxx>
> > ---
> >   fs/ceph/dir.c        | 13 +++++++------
> >   fs/ceph/inode.c      |  5 +++--
> >   fs/ceph/mds_client.c |  2 +-
> >   3 files changed, 11 insertions(+), 9 deletions(-)
> >
> > diff --git a/fs/ceph/dir.c b/fs/ceph/dir.c
> > index a449f4a07c07..6be0c1f793c2 100644
> > --- a/fs/ceph/dir.c
> > +++ b/fs/ceph/dir.c
> > @@ -534,6 +534,13 @@ static int ceph_readdir(struct file *file, struct dir_context *ctx)
> >   					    .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;
> > +		}
> > +
> >   		BUG_ON(rde->offset < ctx->pos);
> >   		BUG_ON(!rde->inode.in);
> >   
> > @@ -542,12 +549,6 @@ static int ceph_readdir(struct file *file, struct dir_context *ctx)
> >   		     i, rinfo->dir_nr, ctx->pos,
> >   		     rde->name_len, rde->name, &rde->inode.in);
> >   
> > -		err = ceph_fname_to_usr(&fname, &tname, &oname, NULL);
> > -		if (err) {
> > -			dout("Unable to decode %.*s. Skipping it.\n", rde->name_len, rde->name);
> > -			continue;
> > -		}
> > -
> >   		if (!dir_emit(ctx, oname.name, oname.len,
> >   			      ceph_present_ino(inode->i_sb, le64_to_cpu(rde->inode.in->ino)),
> >   			      le32_to_cpu(rde->inode.in->mode) >> 12)) {
> > diff --git a/fs/ceph/inode.c b/fs/ceph/inode.c
> > index 8b0832271fdf..2bc2f02b84e8 100644
> > --- a/fs/ceph/inode.c
> > +++ b/fs/ceph/inode.c
> > @@ -1898,8 +1898,9 @@ int ceph_readdir_prepopulate(struct ceph_mds_request *req,
> >   
> >   		err = ceph_fname_to_usr(&fname, &tname, &oname, &is_nokey);
> >   		if (err) {
> > -			dout("Unable to decode %.*s. Skipping it.", rde->name_len, rde->name);
> > -			continue;
> > +			pr_err("%s unable to decode %.*s, got %d\n", __func__,
> > +			       rde->name_len, rde->name, err);
> > +			goto out;
> >   		}
> >   
>
> Is this really an improvement?

Yeah, if we just continue without setting the rde->offset it will crash 
in "BUG_ON(rde->offset < ctx->pos);" in ceph_readdir().


> Suppose I have one dentry with a corrupt
> name. Do I want to fail a readdir request which might allow me to get at
> other dentries in that directory that isn't corrupt?

It's a little hard to handle the code in ceph_readdir():

 503         /* search start position */
 504         if (rinfo->dir_nr > 0) {
 505                 int step, nr = rinfo->dir_nr;
 506                 while (nr > 0) {
 507                         step = nr >> 1;
 508                         if (rinfo->dir_entries[i + step].offset < 
ctx->pos) {
 509                                 i +=  step + 1;
 510                                 nr -= step + 1;
 511                         } else {
 512                                 nr = step;
 513                         }
 514                 }
 515         }

In this case how to set the rde->offset ?


> Maybe we should try to emit some placeholder there?
>
>
> >   		dname.name = oname.name;
> > diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
> > index 914a6e68bb56..94b4c6508044 100644
> > --- a/fs/ceph/mds_client.c
> > +++ b/fs/ceph/mds_client.c
> > @@ -3474,7 +3474,7 @@ static void handle_reply(struct ceph_mds_session *session, struct ceph_msg *msg)
> >   	if (err == 0) {
> >   		if (result == 0 && (req->r_op == CEPH_MDS_OP_READDIR ||
> >   				    req->r_op == CEPH_MDS_OP_LSSNAP))
> > -			ceph_readdir_prepopulate(req, req->r_session);
> > +			err = ceph_readdir_prepopulate(req, req->r_session);
> >   	}
> >   	current->journal_info = NULL;
> >   	mutex_unlock(&req->r_fill_mutex);