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

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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@zx2c4.com>
CC: stable@vger.kernel.org
Fixes: 148a1bc84398 ("drivers: char: mem: Check {read,write}_kmem() addresses")
Signed-off-by: Robin Murphy <robin.murphy@arm.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

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[PATCH] drivers: char: mem: Fix thinko in kmem address checks Robin Murphy <robin.murphy@arm.com> - 2017-01-04 12:40 +0100
  Re: [PATCH] drivers: char: mem: Fix thinko in kmem address checks Greg KH <gregkh@linuxfoundation.org> - 2017-01-04 12:50 +0100
    Re: [PATCH] drivers: char: mem: Fix thinko in kmem address checks Greg KH <gregkh@linuxfoundation.org> - 2017-01-04 18:30 +0100
  [PATCH v2] drivers: char: mem: Fix thinkos in kmem address checks Robin Murphy <robin.murphy@arm.com> - 2017-01-05 18:20 +0100
    Re: [PATCH v2] drivers: char: mem: Fix thinkos in kmem address checks Greg KH <gregkh@linuxfoundation.org> - 2017-01-10 18:50 +0100
      Re: [PATCH v2] drivers: char: mem: Fix thinkos in kmem address checks "Jason A. Donenfeld" <Jason@zx2c4.com> - 2017-01-11 20:20 +0100

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