[tip:locking/urgent] futex: Sanitize user address in set_robust_list()

[tip-bot for Peter Zijlstra <tipbot@zytor.com>]

Commit-ID:  8f3365e34f7519904d78d9fb6dd9e4bae606b9b5
Gitweb:     https://git.kernel.org/tip/8f3365e34f7519904d78d9fb6dd9e4bae606b9b5
Author:     Peter Zijlstra <peterz@infradead.org>
AuthorDate: Wed, 6 Dec 2017 22:40:08 +0100
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Thu, 28 Dec 2017 15:19:12 +0100

futex: Sanitize user address in set_robust_list()

Passing in unaligned variables messes up cmpxchg on a whole bunch of
architectures and causes a in kernel lockup when the robust list is
accessed. Also, not respecting the natural alignment of data structures is
pretty dumb to begin with.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: dvhart@infradead.org
Cc: xiexiuqi@huawei.com
Cc: Cheng Jian <cj.chengjian@huawei.com>
Cc: huawei.libin@huawei.com
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20171206214007.GI3857@worktop
---
 include/uapi/asm-generic/errno.h | 1 +
 kernel/futex.c                   | 5 +++++
 2 files changed, 6 insertions(+)

diff --git a/include/uapi/asm-generic/errno.h b/include/uapi/asm-generic/errno.h
index cf9c51a..e306ee4 100644
--- a/include/uapi/asm-generic/errno.h
+++ b/include/uapi/asm-generic/errno.h
@@ -119,5 +119,6 @@
 #define ERFKILL		132	/* Operation not possible due to RF-kill */
 
 #define EHWPOISON	133	/* Memory page has hardware error */
+#define EMORON		134	/* User did something particularly silly */
 
 #endif
diff --git a/kernel/futex.c b/kernel/futex.c
index 57d0b36..4f471aa 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -3262,6 +3262,8 @@ out:
 SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
 		size_t, len)
 {
+	unsigned long address = (unsigned long)head;
+
 	if (!futex_cmpxchg_enabled)
 		return -ENOSYS;
 	/*
@@ -3270,6 +3272,9 @@ SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
 	if (unlikely(len != sizeof(*head)))
 		return -EINVAL;
 
+	if (unlikely(address % __alignof__(*head)))
+		return -EMORON;
+
 	current->robust_list = head;
 
 	return 0;