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

commit 32043fa065b51e0b1433e48d118821c71b5cd65d upstream.

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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kernel/cpu/mtrr/if.c b/arch/x86/kernel/cpu/mtrr/if.c
index 6d9b455491097a7a68c89b7996d96f0d0e5bb2e1..d5b2a08e2b66b762fc6f2bf9ab549c386f103af2 100644 (file)
--- a/arch/x86/kernel/cpu/mtrr/if.c
+++ b/arch/x86/kernel/cpu/mtrr/if.c
@@ -172,6 +172,8 @@ 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: