nfs: cap request size to fit a kmalloced page array

pNFS servers may return arbitrarily large layouts.  Trim back the I/O size
to one that we can at least allocate the page array for.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/fs/nfs/pagelist.c b/fs/nfs/pagelist.c
index be7cbce6e4c7..94e16ec88312 100644
--- a/fs/nfs/pagelist.c
+++ b/fs/nfs/pagelist.c
@@ -481,6 +481,14 @@ size_t nfs_generic_pg_test(struct nfs_pageio_descriptor *desc,
                 return 0;
         }
 
+        /*
+         * Limit the request size so that we can still allocate a page array
+         * for it without upsetting the slab allocator.
+         */
+        if (((desc->pg_count + req->wb_bytes) >> PAGE_SHIFT) *
+                        sizeof(struct page) > PAGE_SIZE)
+                return 0;
+
         return min(desc->pg_bsize - desc->pg_count, (size_t)req->wb_bytes);
 }
 EXPORT_SYMBOL_GPL(nfs_generic_pg_test);