[PATCH 4.15 46/72] /dev/mem: Avoid overwriting "err" in read_mem()

[Greg Kroah-Hartman]

4.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Kees Cook <keesc...@chromium.org>

commit b5b38200ebe54879a7264cb6f33821f61c586a7e upstream.

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

Reported-by: Brad Spengler <spen...@grsecurity.net>
Fixes: 22ec1a2aea73 ("/dev/mem: Add bounce buffer for copy-out")
Cc: sta...@vger.kernel.org
Signed-off-by: Kees Cook <keesc...@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 drivers/char/mem.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -137,7 +137,7 @@ 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);
 
@@ -160,9 +160,9 @@ 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);