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Subject[PATCH 4.14 151/164] afs: Fix total-length calculation for multiple-page send
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4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: David Howells <dhowells@redhat.com>


[ Upstream commit 1199db603511d7463d9d3840f96f61967affc766 ]

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>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/afs/rxrpc.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)

--- a/fs/afs/rxrpc.c
+++ b/fs/afs/rxrpc.c
@@ -377,8 +377,17 @@ int afs_make_call(struct in_addr *addr,
*/
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 */

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