[PATCH 5.19 197/717] NFSD: Protect against send buffer overflow in NFSv2 READDIR

Greg Kroah-Hartman
2022-10-22T07:53:46Z

From: Chuck Lever <chuck.lever@oracle.com>

[ Upstream commit 00b4492686e0497fdb924a9d4c8f6f99377e176c ]

Restore the previous limit on the @count argument to prevent a
buffer overflow attack.

Fixes: 53b1119a6e50 ("NFSD: Fix READDIR buffer overflow")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/nfsd/nfsproc.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/fs/nfsd/nfsproc.c b/fs/nfsd/nfsproc.c
index 16cde315f454..f65eba938a57 100644
--- a/fs/nfsd/nfsproc.c
+++ b/fs/nfsd/nfsproc.c
@@ -557,12 +557,11 @@ static void nfsd_init_dirlist_pages(struct svc_rqst *rqstp,
struct xdr_buf *buf = &resp->dirlist;
struct xdr_stream *xdr = &resp->xdr;

- count = clamp(count, (u32)(XDR_UNIT * 2), svc_max_payload(rqstp));
-
memset(buf, 0, sizeof(*buf));

/* Reserve room for the NULL ptr & eof flag (-2 words) */
- buf->buflen = count - XDR_UNIT * 2;
+ buf->buflen = clamp(count, (u32)(XDR_UNIT * 2), (u32)PAGE_SIZE);
+ buf->buflen -= XDR_UNIT * 2;
buf->pages = rqstp->rq_next_page;
rqstp->rq_next_page++;

--
2.35.1