linux-kernel - [PATCH] lib: Add might_fault() to strncpy_from

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Date:   Wed, 15 Apr 2020 00:57:05 +0200
From:   KP Singh <kpsingh@...omium.org>
To:     linux-kernel@...r.kernel.org
Cc:     Jann Horn <jannh@...gle.com>,
        Christophe Leroy <christophe.leroy@....fr>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH] lib: Add might_fault() to strncpy_from_user.

From: KP Singh <kpsingh@...gle.com>

When updating a piece of broken logic from using get_user to
strncpy_from_user, we noticed that a warning which is expected when
calling a function that might fault from an atomic context with
pagefaults enabled disappeared.

Not having this warning in place can lead to calling strncpy_from_user
from an atomic context and eventually kernel crashes/stack corruption.

Cc: Jann Horn <jannh@...gle.com>

Signed-off-by: KP Singh <kpsingh@...gle.com>
---
 lib/strncpy_from_user.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/lib/strncpy_from_user.c b/lib/strncpy_from_user.c
index 706020b06617..16e78d0bb5d4 100644
--- a/lib/strncpy_from_user.c
+++ b/lib/strncpy_from_user.c
@@ -98,6 +98,7 @@ long strncpy_from_user(char *dst, const char __user *src, long count)
 {
 	unsigned long max_addr, src_addr;
 
+	might_fault();
 	if (unlikely(count <= 0))
 		return 0;
 
-- 
2.26.0.110.g2183baf09c-goog