linux-kernel - [PATCH 5.4 067/118] um: ubd: Prevent buffer overrun on command completion

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Message-Id: <20200422095042.899761587@linuxfoundation.org>
Date:   Wed, 22 Apr 2020 11:57:08 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Martyn Welch <martyn.welch@...labora.com>,
        Gabriel Krisman Bertazi <krisman@...labora.com>,
        Richard Weinberger <richard@....at>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.4 067/118] um: ubd: Prevent buffer overrun on command completion

From: Gabriel Krisman Bertazi <krisman@...labora.com>

[ Upstream commit 6e682d53fc1ef73a169e2a5300326cb23abb32ee ]

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@...labora.com>
Signed-off-by: Gabriel Krisman Bertazi <krisman@...labora.com>
Signed-off-by: Richard Weinberger <richard@....at>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/um/drivers/ubd_kern.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/um/drivers/ubd_kern.c b/arch/um/drivers/ubd_kern.c
index 6627d7c30f370..0f5d0a699a49b 100644
--- a/arch/um/drivers/ubd_kern.c
+++ b/arch/um/drivers/ubd_kern.c
@@ -1606,7 +1606,9 @@ 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;
 			}
-- 
2.20.1