From 0d32a6bbb8e7bf503855f2990f1ccce0922db87b Mon Sep 17 00:00:00 2001 From: Chuck Lever Date: Wed, 27 Sep 2023 13:16:48 -0400 Subject: NFSD: Fix zero NFSv4 READ results when RQ_SPLICE_OK is not set MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit nfsd4_encode_readv() uses xdr->buf->page_len as a starting point for the nfsd_iter_read() sink buffer -- page_len is going to be offset by the parts of the COMPOUND that have already been encoded into xdr->buf->pages. However, that value must be captured /before/ xdr_reserve_space_vec() advances page_len by the expected size of the read payload. Otherwise, the whole front part of the first page of the payload in the reply will be uninitialized. Mantas hit this because sec=krb5i forces RQ_SPLICE_OK off, which invokes the readv part of the nfsd4_encode_read() path. Also, older Linux NFS clients appear to send shorter READ requests for files smaller than a page, whereas newer clients just send page-sized requests and let the server send as many bytes as are in the file. Reported-by: Mantas Mikulėnas Closes: https://lore.kernel.org/linux-nfs/f1d0b234-e650-0f6e-0f5d-126b3d51d1eb@gmail.com/ Fixes: 703d75215555 ("NFSD: Hoist rq_vec preparation into nfsd_read() [step two]") Signed-off-by: Chuck Lever --- fs/nfsd/nfs4xdr.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'fs') diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c index 2e40c74d2f72..92c7dde148a4 100644 --- a/fs/nfsd/nfs4xdr.c +++ b/fs/nfsd/nfs4xdr.c @@ -4113,6 +4113,7 @@ static __be32 nfsd4_encode_readv(struct nfsd4_compoundres *resp, struct file *file, unsigned long maxcount) { struct xdr_stream *xdr = resp->xdr; + unsigned int base = xdr->buf->page_len & ~PAGE_MASK; unsigned int starting_len = xdr->buf->len; __be32 zero = xdr_zero; __be32 nfserr; @@ -4121,8 +4122,7 @@ static __be32 nfsd4_encode_readv(struct nfsd4_compoundres *resp, return nfserr_resource; nfserr = nfsd_iter_read(resp->rqstp, read->rd_fhp, file, - read->rd_offset, &maxcount, - xdr->buf->page_len & ~PAGE_MASK, + read->rd_offset, &maxcount, base, &read->rd_eof); read->rd_length = maxcount; if (nfserr) -- cgit v1.2.3