NFSD: Protect against send buffer overflow in NFSv2 READDIR

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>

diff --git a/fs/nfsd/nfsproc.c b/fs/nfsd/nfsproc.c
index 7381972..ddb1902 100644 (file)
--- a/fs/nfsd/nfsproc.c
+++ b/fs/nfsd/nfsproc.c
@@ -567,12 +567,11 @@ 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++;