From: Kees Cook <keescook@chromium.org>
Date: Tue, 27 Mar 2018 14:06:14 -0700
Subject: /dev/mem: Avoid overwriting "err" in read_mem()
Git-commit: b5b38200ebe54879a7264cb6f33821f61c586a7e
Patch-mainline: v4.17-rc1
References: git-fixes

Successes in probe_kernel_read() would mask failures in copy_to_user()
during read_mem().

Reported-by: Brad Spengler <spender@grsecurity.net>
Fixes: 22ec1a2aea73 ("/dev/mem: Add bounce buffer for copy-out")
Cc: stable@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 drivers/char/mem.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -136,7 +136,7 @@ static ssize_t read_mem(struct file *fil
 
 	while (count > 0) {
 		unsigned long remaining;
-		int allowed;
+		int allowed, probe;
 
 		sz = size_inside_page(p, count);
 
@@ -159,9 +159,9 @@ static ssize_t read_mem(struct file *fil
 			if (!ptr)
 				goto failed;
 
-			err = probe_kernel_read(bounce, ptr, sz);
+			probe = probe_kernel_read(bounce, ptr, sz);
 			unxlate_dev_mem_ptr(p, ptr);
-			if (err)
+			if (probe)
 				goto failed;
 
 			remaining = copy_to_user(buf, bounce, sz);