[PATCH AUTOSEL 5.6 060/129] um: ubd: Prevent buffer overrun on command completion

Sasha Levin
2020-04-15T13:07:27Z

From: Gabriel Krisman Bertazi <krisman@collabora.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@collabora.com>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Sasha Levin <sashal@kernel.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 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;
}
--
2.20.1