afs: Fix total-length calculation for multiple-page send

Fix the total-length calculation in afs_make_call() when the operation
being dispatched has data from a series of pages attached.

Despite the patched code looking like that it should reduce mathematically
to the current code, it doesn't because the 32-bit unsigned arithmetic
being used to calculate the page-offset-difference doesn't correctly extend
to a 64-bit value when the result is effectively negative.

Without this, some FS.StoreData operations that span multiple pages fail,
reporting too little or too much data.

Signed-off-by: David Howells <dhowells@redhat.com>

diff --git a/fs/afs/rxrpc.c b/fs/afs/rxrpc.c
index 21f43d3acb91a0b52cd570676c96ddae41c856ac..1d075696bf5502c6453d35f1e2f4c5bf62899785 100644 (file)
--- a/fs/afs/rxrpc.c
+++ b/fs/afs/rxrpc.c
@@ -350,8 +350,17 @@ long afs_make_call(struct afs_addr_cursor *ac, struct afs_call *call,
         */
        tx_total_len = call->request_size;
        if (call->send_pages) {
-               tx_total_len += call->last_to - call->first_offset;
-               tx_total_len += (call->last - call->first) * PAGE_SIZE;
+               if (call->last == call->first) {
+                       tx_total_len += call->last_to - call->first_offset;
+               } else {
+                       /* It looks mathematically like you should be able to
+                        * combine the following lines with the ones above, but
+                        * unsigned arithmetic is fun when it wraps...
+                        */
+                       tx_total_len += PAGE_SIZE - call->first_offset;
+                       tx_total_len += call->last_to;
+                       tx_total_len += (call->last - call->first - 1) * PAGE_SIZE;
+               }
        }
 
        /* create a call */