On Fri, 12 Sep 2025, Chuck Lever wrote: > From: Chuck Lever <chuck.lever@xxxxxxxxxx> > > The *count parameter does not appear to be explicitly restricted > to being smaller than rsize, so it might be possible to overrun > the rq_bvec array. > > Rather than overrunning the array (damage done!) and then WARNING > once, let's harden the loop so that it terminates before the end of > rq_bvec. This should result in a short read, which is OK (clients > recover by sending additional READ requests for the remaining unread > bytes). > > Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx> > --- > fs/nfsd/vfs.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > There might be a similar issue with rq_next_page in this loop? > > Suppose that nfsd4_encode_readv() encounters a second READ operation > in a COMPOUND, and the two READ operations together comprise more > than "rsize" total bytes of payload. Each rq_bvec is under the page > limit, but the total number of pages consumed from rq_pages might > exceed rq_maxpages. > > diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c > index 714777c221ed..e2f0fe3f82c0 100644 > --- a/fs/nfsd/vfs.c > +++ b/fs/nfsd/vfs.c > @@ -1120,13 +1120,13 @@ __be32 nfsd_iter_read(struct svc_rqst *rqstp, struct svc_fh *fhp, > bvec_set_page(&rqstp->rq_bvec[v], *(rqstp->rq_next_page++), > len, base); > total -= len; > - ++v; > base = 0; > + if (++v >= rqstp->rq_maxpages) > + break; I would have changed the head of the while loop to be while (total > 0 && rqstp->rq_next_page < ....) and then realised that I don't know what to put there. I don't think that counting up to rq_maxpages is safe when there could be two READ ops in an NFSv4 Compound. And if we are cleaning up this function I woul put the increments of v and rq_next_page next to each other.. </bikeshed> The patch is an improvement. I wonder if it is enough. Thanks, NeilBrown > } > - WARN_ON_ONCE(v > rqstp->rq_maxpages); > > - trace_nfsd_read_vector(rqstp, fhp, offset, *count); > - iov_iter_bvec(&iter, ITER_DEST, rqstp->rq_bvec, v, *count); > + trace_nfsd_read_vector(rqstp, fhp, offset, *count - total); > + iov_iter_bvec(&iter, ITER_DEST, rqstp->rq_bvec, v, *count - total); > host_err = vfs_iocb_iter_read(file, &kiocb, &iter); > return nfsd_finish_read(rqstp, fhp, file, offset, count, eof, host_err); > } > -- > 2.50.0 > >
