NFS: Check lengths more thoroughly in NFS4 readdir XDR decode

Check the bounds of length specifiers more thoroughly in the XDR decoding of
NFS4 readdir reply data.

Currently, if the server returns a bitmap or attr length that causes the
current decode point pointer to wrap, this could go undetected (consider a
small "negative" length on a 32-bit machine).

Also add a check into the main XDR decode handler to make sure that the amount
of data is a multiple of four bytes (as specified by RFC-1014).  This makes
sure that we can do u32* pointer subtraction in the NFS client without risking
an undefined result (the result is undefined if the pointers are not correctly
aligned with respect to one another).

Signed-Off-By: David Howells <dhowells@redhat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
(cherry picked from 5861fddd64a7eaf7e8b1a9997455a24e7f688092 commit)

1 files changed, 11 insertions, 10 deletions

diff --git a/fs/nfs/nfs4xdr.c b/fs/nfs/nfs4xdr.c
index 1750d996f49f..730ec8fb31c6 100644
--- a/fs/nfs/nfs4xdr.c
+++ b/fs/nfs/nfs4xdr.c
@@ -3355,7 +3355,7 @@ static int decode_readdir(struct xdr_stream *xdr, struct rpc_rqst *req, struct n
         struct kvec     *iov = rcvbuf->head;
         unsigned int    nr, pglen = rcvbuf->page_len;
         uint32_t        *end, *entry, *p, *kaddr;
-        uint32_t        len, attrlen;
+        uint32_t        len, attrlen, xlen;
         int             hdrlen, recvd, status;
 
         status = decode_op_hdr(xdr, OP_READDIR);
@@ -3377,10 +3377,10 @@ static int decode_readdir(struct xdr_stream *xdr, struct rpc_rqst *req, struct n
 
         BUG_ON(pglen + readdir->pgbase > PAGE_CACHE_SIZE);
         kaddr = p = (uint32_t *) kmap_atomic(page, KM_USER0);
-        end = (uint32_t *) ((char *)p + pglen + readdir->pgbase);
+        end = p + ((pglen + readdir->pgbase) >> 2);
         entry = p;
         for (nr = 0; *p++; nr++) {
-                if (p + 3 > end)
+                if (end - p < 3)
                         goto short_pkt;
                 dprintk("cookie = %Lu, ", *((unsigned long long *)p));
                 p += 2;                 /* cookie */
@@ -3389,18 +3389,19 @@ static int decode_readdir(struct xdr_stream *xdr, struct rpc_rqst *req, struct n
                         printk(KERN_WARNING "NFS: giant filename in readdir (len 0x%x)\n", len);
                         goto err_unmap;
                 }
-                dprintk("filename = %*s\n", len, (char *)p);
-                p += XDR_QUADLEN(len);
-                if (p + 1 > end)
+                xlen = XDR_QUADLEN(len);
+                if (end - p < xlen + 1)
                         goto short_pkt;
+                dprintk("filename = %*s\n", len, (char *)p);
+                p += xlen;
                 len = ntohl(*p++);      /* bitmap length */
-                p += len;
-                if (p + 1 > end)
+                if (end - p < len + 1)
                         goto short_pkt;
+                p += len;
                 attrlen = XDR_QUADLEN(ntohl(*p++));
-                p += attrlen;           /* attributes */
-                if (p + 2 > end)
+                if (end - p < attrlen + 2)
                         goto short_pkt;
+                p += attrlen;           /* attributes */
                 entry = p;
         }
         if (!nr && (entry[0] != 0 || entry[1] == 0))