NFS: Don't attempt to decode missing directory entries

If a READDIR reply comes back without any page data, avoid a NULL pointer
dereference in xdr_copy_to_scratch().

BUG: unable to handle kernel NULL pointer dereference at 0000000000000001
IP: [<ffffffff813a378d>] memcpy+0xd/0x110
...
Call Trace:
	? xdr_inline_decode+0x7a/0xb0 [sunrpc]
	nfs3_decode_dirent+0x73/0x320 [nfsv3]
	nfs_readdir_page_filler+0xd5/0x4e0 [nfs]
	? nfs3_rpc_wrapper.constprop.9+0x42/0xc0 [nfsv3]
	nfs_readdir_xdr_to_array+0x1fa/0x330 [nfs]
	? mem_cgroup_commit_charge+0xac/0x160
	? nfs_readdir_xdr_to_array+0x330/0x330 [nfs]
	nfs_readdir_filler+0x22/0x90 [nfs]
	do_read_cache_page+0x7e/0x1a0
	read_cache_page+0x1c/0x20
	nfs_readdir+0x18e/0x660 [nfs]
	? nfs3_xdr_dec_getattr3res+0x80/0x80 [nfsv3]
	iterate_dir+0x97/0x130
	SyS_getdents+0x94/0x120
	? fillonedir+0xd0/0xd0
	system_call_fastpath+0x12/0x17

Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index c19e16f..a00ba92 100644 (file)
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -544,6 +544,9 @@ int nfs_readdir_page_filler(nfs_readdir_descriptor_t *desc, struct nfs_entry *en
        if (scratch == NULL)
                return -ENOMEM;
 
+       if (buflen == 0)
+               goto out_nopages;
+
        xdr_init_decode_pages(&stream, &buf, xdr_pages, buflen);
        xdr_set_scratch_buffer(&stream, page_address(scratch), PAGE_SIZE);
 
@@ -565,6 +568,7 @@ int nfs_readdir_page_filler(nfs_readdir_descriptor_t *desc, struct nfs_entry *en
                        break;
        } while (!entry->eof);
 
+out_nopages:
        if (count == 0 || (status == -EBADCOOKIE && entry->eof != 0)) {
                array = nfs_readdir_get_array(page);
                if (!IS_ERR(array)) {