[PATCH AUTOSEL 4.4 16/21] x86/mtrr: Don't copy uninitialized gentry fields back to userspace

[Sasha Levin <sashal@kernel.org>]

From: Colin Ian King <colin.king@canonical.com>

[ Upstream commit 32043fa065b51e0b1433e48d118821c71b5cd65d ]

Currently the copy_to_user of data in the gentry struct is copying
uninitiaized data in field _pad from the stack to userspace.

Fix this by explicitly memset'ing gentry to zero, this also will zero any
compiler added padding fields that may be in struct (currently there are
none).

Detected by CoverityScan, CID#200783 ("Uninitialized scalar variable")

Fixes: b263b31e8ad6 ("x86, mtrr: Use explicit sizing and padding for the 64-bit ioctls")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Tyler Hicks <tyhicks@canonical.com>
Cc: security@kernel.org
Link: https://lkml.kernel.org/r/20181218172956.1440-1-colin.king@canonical.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/x86/kernel/cpu/mtrr/if.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/kernel/cpu/mtrr/if.c b/arch/x86/kernel/cpu/mtrr/if.c
index d76f13d6d8d6..ec894bf5eeb0 100644
--- a/arch/x86/kernel/cpu/mtrr/if.c
+++ b/arch/x86/kernel/cpu/mtrr/if.c
@@ -173,6 +173,8 @@ mtrr_ioctl(struct file *file, unsigned int cmd, unsigned long __arg)
 	struct mtrr_gentry gentry;
 	void __user *arg = (void __user *) __arg;
 
+	memset(&gentry, 0, sizeof(gentry));
+
 	switch (cmd) {
 	case MTRRIOC_ADD_ENTRY:
 	case MTRRIOC_SET_ENTRY:
-- 
2.19.1