[patch 23/86] kernel/sys.c: avoid copying possible padding bytes in copy_to_user

Andrew Morton
2019-12-05T00:50:56Z

From: Joe Perches <joe@perches.com>
Subject: kernel/sys.c: avoid copying possible padding bytes in copy_to_user

Initialization is not guaranteed to zero padding bytes so use an explicit
memset instead to avoid leaking any kernel content in any possible padding
bytes.

Link: http://lkml.kernel.org/r/dfa331c00881d61c8ee51577a082d8bebd61805c.camel@perches.com
Signed-off-by: Joe Perches <joe@perches.com>
Cc: Dan Carpenter <error27@gmail.com>
Cc: Julia Lawall <julia.lawall@lip6.fr>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

kernel/sys.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

--- a/kernel/sys.c~kernel-sysc-avoid-copying-possible-padding-bytes-in-copy_to_user
+++ a/kernel/sys.c
@@ -1279,11 +1279,13 @@ SYSCALL_DEFINE1(uname, struct old_utsnam

SYSCALL_DEFINE1(olduname, struct oldold_utsname __user *, name)
{
- struct oldold_utsname tmp = {};
+ struct oldold_utsname tmp;

if (!name)
return -EFAULT;

+ memset(&tmp, 0, sizeof(tmp));
+
down_read(&uts_sem);
memcpy(&tmp.sysname, &utsname()->sysname, __OLD_UTS_LEN);
memcpy(&tmp.nodename, &utsname()->nodename, __OLD_UTS_LEN);
_