linux-kernel - [PATCH] drivers: char: mem: Fix thinko in kmem address checks

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Message-Id: <641a72e66f81d1244d8420074bc5def88d3929d4.1483529604.git.robin.murphy@arm.com>
Date:   Wed,  4 Jan 2017 11:37:49 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     gregkh@...uxfoundation.org, Jason@...c4.com
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: [PATCH] drivers: char: mem: Fix thinko in kmem address checks

When borrowing the pfn_valid() check from mmap_kmem(), somebody managed
to get physical and virtual addresses spectacularly muddled up, such
that we've ended up with checks for one being the other. Whilst this
does indeed prevent out-of-bounds accesses crashing, on most systems it
also prevents the more desirable use-case of working at all ever.

Check the *virtual* offset correctly for what it is.

Reported-by: Jason A. Donenfeld <Jason@...c4.com>
CC: stable@...r.kernel.org
Fixes: 148a1bc84398 ("drivers: char: mem: Check {read,write}_kmem() addresses")
Signed-off-by: Robin Murphy <robin.murphy@....com>
---
 drivers/char/mem.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 5bb1985ec484..bdc6a4018604 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -381,7 +381,7 @@ static ssize_t read_kmem(struct file *file, char __user *buf,
 	char *kbuf; /* k-addr because vread() takes vmlist_lock rwlock */
 	int err = 0;
 
-	if (!pfn_valid(PFN_DOWN(p)))
+	if (!virt_addr_valid(p))
 		return -EIO;
 
 	read = 0;
@@ -512,7 +512,7 @@ static ssize_t write_kmem(struct file *file, const char __user *buf,
 	char *kbuf; /* k-addr because vwrite() takes vmlist_lock rwlock */
 	int err = 0;
 
-	if (!pfn_valid(PFN_DOWN(p)))
+	if (!virt_addr_valid(p))
 		return -EIO;
 
 	if (p < (unsigned long) high_memory) {
-- 
2.10.2.dirty