[PATCH v3 5/6] NFSD: Insulate nfsd4_encode_fattr4() from page boundaries in the encode buffer

cel
2024-12-26T16:29:01Z

Commit ab04de60ae1c ("NFSD: Optimize nfsd4_encode_fattr()") replaced
the use of write_bytes_to_xdr_buf() because it's expensive and the
data items to be encoded are already properly aligned.

However, there's no guarantee that the pointer returned from
xdr_reserve_space() will still point to the correct reserved space
in the encode buffer after one or more intervening calls to
xdr_reserve_space(). It just happens to work with the current
implementation of xdr_reserve_space().

This commit effectively reverts the optimization.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
fs/nfsd/nfs4xdr.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index b770225d63dc..d4ee633b01e3 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -3506,8 +3506,8 @@ nfsd4_encode_fattr4(struct svc_rqst *rqstp, struct xdr_stream *xdr,
struct nfsd4_fattr_args args;
struct svc_fh *tempfh = NULL;
int starting_len = xdr->buf->len;
- __be32 *attrlen_p, status;
- int attrlen_offset;
+ unsigned int attrlen_offset;
+ __be32 attrlen, status;
u32 attrmask[3];
int err;
struct nfsd4_compoundres *resp = rqstp->rq_resp;
@@ -3627,9 +3627,8 @@ nfsd4_encode_fattr4(struct svc_rqst *rqstp, struct xdr_stream *xdr,
goto out;

/* attr_vals */
- attrlen_offset = xdr->buf->len;
- attrlen_p = xdr_reserve_space(xdr, XDR_UNIT);
- if (!attrlen_p)
+ attrlen_offset = xdr_stream_pos(xdr);
+ if (unlikely(!xdr_reserve_space(xdr, XDR_UNIT)))
goto out_resource;
bitmap_from_arr32(attr_bitmap, attrmask,
ARRAY_SIZE(nfsd4_enc_fattr4_encode_ops));
@@ -3639,7 +3638,8 @@ nfsd4_encode_fattr4(struct svc_rqst *rqstp, struct xdr_stream *xdr,
if (status != nfs_ok)
goto out;
}
- *attrlen_p = cpu_to_be32(xdr->buf->len - attrlen_offset - XDR_UNIT);
+ attrlen = cpu_to_be32(xdr_stream_pos(xdr) - attrlen_offset - XDR_UNIT);
+ write_bytes_to_xdr_buf(xdr->buf, attrlen_offset, &attrlen, XDR_UNIT);
status = nfs_ok;

out:
--
2.47.0