[tip:x86/urgent] x86/mtrr: Don't copy uninitialized gentry fields back to userspace

[tip-bot for Colin Ian King <tipbot@zytor.com>]

Commit-ID:  32043fa065b51e0b1433e48d118821c71b5cd65d
Gitweb:     https://git.kernel.org/tip/32043fa065b51e0b1433e48d118821c71b5cd65d
Author:     Colin Ian King <colin.king@canonical.com>
AuthorDate: Tue, 18 Dec 2018 17:29:56 +0000
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Wed, 19 Dec 2018 00:00:16 +0100

x86/mtrr: Don't copy uninitialized gentry fields back to userspace

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


---
 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 2e173d47b450..4d36dcc1cf87 100644
--- a/arch/x86/kernel/cpu/mtrr/if.c
+++ b/arch/x86/kernel/cpu/mtrr/if.c
@@ -165,6 +165,8 @@ 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: