From c9fc7772bacb28a8bd8efb08399c5af7217fbbb7 Mon Sep 17 00:00:00 2001 From: Chuck Lever Date: Mon, 30 Dec 2024 19:28:54 -0500 Subject: [PATCH] NFSD: Insulate nfsd4_encode_read_plus() from page boundaries in the encode buffer Commit eeadcb757945 ("NFSD: Simplify READ_PLUS") replaced the use of write_bytes_to_xdr_buf(), copying what was in nfsd4_encode_read() at the time. However, the current code will corrupt the encoded data if the XDR data items that are reserved early and then poked into the XDR buffer later happen to fall on a page boundary in the XDR encoding buffer. __xdr_commit_encode can shift encoded data items in the encoding buffer so that pointers returned from xdr_reserve_space() no longer address the same part of the encoding stream. Fixes: eeadcb757945 ("NFSD: Simplify READ_PLUS") Reviewed-by: NeilBrown Reviewed-by: Jeff Layton Signed-off-by: Chuck Lever --- fs/nfsd/nfs4xdr.c | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-) diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c index 2399b17db052d..474fd663b0a9a 100644 --- a/fs/nfsd/nfs4xdr.c +++ b/fs/nfsd/nfs4xdr.c @@ -5337,16 +5337,17 @@ nfsd4_encode_read_plus(struct nfsd4_compoundres *resp, __be32 nfserr, struct nfsd4_read *read = &u->read; struct file *file = read->rd_nf->nf_file; struct xdr_stream *xdr = resp->xdr; - int starting_len = xdr->buf->len; + unsigned int eof_offset; + __be32 wire_data[2]; u32 segments = 0; - __be32 *p; if (nfserr) return nfserr; - /* eof flag, segment count */ - p = xdr_reserve_space(xdr, 4 + 4); - if (!p) + eof_offset = xdr->buf->len; + + /* Reserve space for the eof flag and segment count */ + if (unlikely(!xdr_reserve_space(xdr, XDR_UNIT * 2))) return nfserr_io; xdr_commit_encode(xdr); @@ -5356,15 +5357,16 @@ nfsd4_encode_read_plus(struct nfsd4_compoundres *resp, __be32 nfserr, nfserr = nfsd4_encode_read_plus_data(resp, read); if (nfserr) { - xdr_truncate_encode(xdr, starting_len); + xdr_truncate_encode(xdr, eof_offset); return nfserr; } segments++; out: - p = xdr_encode_bool(p, read->rd_eof); - *p = cpu_to_be32(segments); + wire_data[0] = read->rd_eof ? xdr_one : xdr_zero; + wire_data[1] = cpu_to_be32(segments); + write_bytes_to_xdr_buf(xdr->buf, eof_offset, &wire_data, XDR_UNIT * 2); return nfserr; } -- 2.39.5