linux-kernel - [PATCH] futex: Fix fault_in_user

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Date:   Mon, 16 Aug 2021 14:54:17 +0800
From:   Huacai Chen <chenhuacai@...ngson.cn>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Darren Hart <dvhart@...radead.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Cc:     linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        Xuefeng Li <lixuefeng@...ngson.cn>,
        Huacai Chen <chenhuacai@...il.com>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Huacai Chen <chenhuacai@...ngson.cn>,
        Hongchen Zhang <zhanghongchen@...ngson.cn>
Subject: [PATCH] futex: Fix fault_in_user_writeable()

fault_in_user_writeable() should verify R/W access but only verify W. In
most archs W implies R, but not true in MIPS and LoongArch, so fix it.

Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>
Signed-off-by: Hongchen Zhang <zhanghongchen@...ngson.cn>
---
 kernel/futex.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index 2ecb07575055..c3b68be31bf3 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -672,10 +672,15 @@ static int get_futex_key(u32 __user *uaddr, bool fshared, union futex_key *key,
  */
 static int fault_in_user_writeable(u32 __user *uaddr)
 {
-	struct mm_struct *mm = current->mm;
 	int ret;
+	struct mm_struct *mm = current->mm;
+	struct vm_area_struct *vma;
 
 	mmap_read_lock(mm);
+	vma = find_vma(mm, (unsigned long)uaddr);
+	if (!(vma->vm_flags & VM_READ))
+		ret = -EFAULT;
+
 	ret = fixup_user_fault(mm, (unsigned long)uaddr,
 			       FAULT_FLAG_WRITE, NULL);
 	mmap_read_unlock(mm);
-- 
2.27.0