From: Gabriel Krisman Bertazi <krisman@collabora.com>
Date: Tue, 17 Mar 2020 00:45:06 +0000 (-0400)
Subject: um: ubd: Prevent buffer overrun on command completion
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=6e682d53fc1ef73a169e2a5300326cb23abb32ee;p=linux.git

um: ubd: Prevent buffer overrun on command completion

On the hypervisor side, when completing commands and the pipe is full,
we retry writing only the entries that failed, by offsetting
io_req_buffer, but we don't reduce the number of bytes written, which
can cause a buffer overrun of io_req_buffer, and write garbage to the
pipe.

Cc: Martyn Welch <martyn.welch@collabora.com>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
---

diff --git a/arch/um/drivers/ubd_kern.c b/arch/um/drivers/ubd_kern.c
index 247f95da057b5..eca45ad2166c9 100644
--- a/arch/um/drivers/ubd_kern.c
+++ b/arch/um/drivers/ubd_kern.c
@@ -1607,7 +1607,9 @@ int io_thread(void *arg)
 		written = 0;
 
 		do {
-			res = os_write_file(kernel_fd, ((char *) io_req_buffer) + written, n);
+			res = os_write_file(kernel_fd,
+					    ((char *) io_req_buffer) + written,
+					    n - written);
 			if (res >= 0) {
 				written += res;
 			}