nfsd/nfsd3_proc_readdir: fix buffer count and page pointers

After this commit
  f875a79 nfsd: allow nfsv3 readdir request to be larger.
nfsv3 readdir request size can be larger than PAGE_SIZE. So if the
directory been read is large enough, we can use multiple pages
in rq_respages. Update buffer count and page pointers like we do
in readdirplus to make this happen.

Now listing a directory within 3000 files will panic because we
are counting in a wrong way and would write on random page.

Fixes: f875a79 "nfsd: allow nfsv3 readdir request to be larger"
Signed-off-by: Murphy Zhou <jencce.kernel@gmail.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

2 files changed, 24 insertions, 4 deletions

diff --git a/fs/nfsd/nfs3proc.c b/fs/nfsd/nfs3proc.c
index 8f933e84cec1..9bc32af4e2da 100644
--- a/fs/nfsd/nfs3proc.c
+++ b/fs/nfsd/nfs3proc.c
@@ -442,7 +442,9 @@ nfsd3_proc_readdir(struct svc_rqst *rqstp)
         struct nfsd3_readdirargs *argp = rqstp->rq_argp;
         struct nfsd3_readdirres  *resp = rqstp->rq_resp;
         __be32          nfserr;
-        int             count;
+        int             count = 0;
+        struct page     **p;
+        caddr_t         page_addr = NULL;
 
         dprintk("nfsd: READDIR(3)  %s %d bytes at %d\n",
                                 SVCFH_fmt(&argp->fh),
@@ -462,7 +464,18 @@ nfsd3_proc_readdir(struct svc_rqst *rqstp)
         nfserr = nfsd_readdir(rqstp, &resp->fh, (loff_t*) &argp->cookie, 
                                         &resp->common, nfs3svc_encode_entry);
         memcpy(resp->verf, argp->verf, 8);
-        resp->count = resp->buffer - argp->buffer;
+        count = 0;
+        for (p = rqstp->rq_respages + 1; p < rqstp->rq_next_page; p++) {
+                page_addr = page_address(*p);
+
+                if (((caddr_t)resp->buffer >= page_addr) &&
+                    ((caddr_t)resp->buffer < page_addr + PAGE_SIZE)) {
+                        count += (caddr_t)resp->buffer - page_addr;
+                        break;
+                }
+                count += PAGE_SIZE;
+        }
+        resp->count = count >> 2;
         if (resp->offset) {
                 loff_t offset = argp->cookie;
 
diff --git a/fs/nfsd/nfs3xdr.c b/fs/nfsd/nfs3xdr.c
index 93fea246f676..8d789124ed3c 100644
--- a/fs/nfsd/nfs3xdr.c
+++ b/fs/nfsd/nfs3xdr.c
@@ -573,6 +573,7 @@ int
 nfs3svc_decode_readdirargs(struct svc_rqst *rqstp, __be32 *p)
 {
         struct nfsd3_readdirargs *args = rqstp->rq_argp;
+        int len;
         u32 max_blocksize = svc_max_payload(rqstp);
 
         p = decode_fh(p, &args->fh);
@@ -582,8 +583,14 @@ nfs3svc_decode_readdirargs(struct svc_rqst *rqstp, __be32 *p)
         args->verf   = p; p += 2;
         args->dircount = ~0;
         args->count  = ntohl(*p++);
-        args->count  = min_t(u32, args->count, max_blocksize);
-        args->buffer = page_address(*(rqstp->rq_next_page++));
+        len = args->count  = min_t(u32, args->count, max_blocksize);
+
+        while (len > 0) {
+                struct page *p = *(rqstp->rq_next_page++);
+                if (!args->buffer)
+                        args->buffer = page_address(p);
+                len -= PAGE_SIZE;
+        }
 
         return xdr_argsize_check(rqstp, p);
 }