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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Christoph Hellwig <hch@lst.de>,
        Arnd Bergmann <arnd@arndb.de>
Subject: [PATCH 5.15 36/37] m68k: fix access_ok for coldfire
Date:   Fri, 25 Mar 2022 16:14:37 +0100
Message-Id: <20220325150420.964665740@linuxfoundation.org>
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From: Arnd Bergmann <arnd@arndb.de>

commit 26509034bef198525d5936c116cbd0c3fa491c0b upstream.

While most m68k platforms use separate address spaces for user
and kernel space, at least coldfire does not, and the other
ones have a TASK_SIZE that is less than the entire 4GB address
range.

Using the default implementation of __access_ok() stops coldfire
user space from trivially accessing kernel memory.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: stable@vger.kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/m68k/include/asm/uaccess.h |   15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

--- a/arch/m68k/include/asm/uaccess.h
+++ b/arch/m68k/include/asm/uaccess.h
@@ -12,14 +12,17 @@
 #include <asm/extable.h>
 
 /* We let the MMU do all checking */
-static inline int access_ok(const void __user *addr,
+static inline int access_ok(const void __user *ptr,
 			    unsigned long size)
 {
-	/*
-	 * XXX: for !CONFIG_CPU_HAS_ADDRESS_SPACES this really needs to check
-	 * for TASK_SIZE!
-	 */
-	return 1;
+	unsigned long limit = TASK_SIZE;
+	unsigned long addr = (unsigned long)ptr;
+
+	if (IS_ENABLED(CONFIG_CPU_HAS_ADDRESS_SPACES) ||
+	    !IS_ENABLED(CONFIG_MMU))
+		return 1;
+
+	return (size <= limit) && (addr <= (limit - size));
 }
 
 /*