[PATCH 5.4 095/191] samples/seccomp: Zero out members based on seccomp_notif_sizes

From: Greg Kroah-Hartman
Date: Tue Jan 07 2020 - 15:59:50 EST

From: Sargun Dhillon <sargun@xxxxxxxxx>

commit 771b894f2f3dfedc2ba5561731fffa0e39b1bbb6 upstream.

The sizes by which seccomp_notif and seccomp_notif_resp are allocated are
based on the SECCOMP_GET_NOTIF_SIZES ioctl. This allows for graceful
extension of these datastructures. If userspace zeroes out the
datastructure based on its version, and it is lagging behind the kernel's
version, it will end up sending trailing garbage. On the other hand,
if it is ahead of the kernel version, it will write extra zero space,
and potentially cause corruption.

Signed-off-by: Sargun Dhillon <sargun@xxxxxxxxx>
Suggested-by: Tycho Andersen <tycho@xxxxxxxx>
Link: https://lore.kernel.org/r/20191230203503.4925-1-sargun@xxxxxxxxx
Fixes: fec7b6690541 ("samples: add an example of seccomp user trap")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

samples/seccomp/user-trap.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/samples/seccomp/user-trap.c
+++ b/samples/seccomp/user-trap.c
@@ -298,14 +298,14 @@ int main(void)
req = malloc(sizes.seccomp_notif);
if (!req)
goto out_close;
- memset(req, 0, sizeof(*req));

resp = malloc(sizes.seccomp_notif_resp);
if (!resp)
goto out_req;
- memset(resp, 0, sizeof(*resp));
+ memset(resp, 0, sizes.seccomp_notif_resp);

while (1) {
+ memset(req, 0, sizes.seccomp_notif);
if (ioctl(listener, SECCOMP_IOCTL_NOTIF_RECV, req)) {
perror("ioctl recv");
goto out_resp;