[PATCH 28/29] drivers: convert sbd_duart.map_guard from atomic_t to refcount_t

Elena Reshetova
2017-03-06T14:21:15Z

refcount_t type and corresponding API should be
used instead of atomic_t when the variable is used as
a reference counter. This allows to avoid accidental
refcounter overflows that might lead to use-after-free
situations.

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David Windsor <dwindsor@gmail.com>
---
drivers/tty/serial/sb1250-duart.c | 18 +++++++-----------
1 file changed, 7 insertions(+), 11 deletions(-)

diff --git a/drivers/tty/serial/sb1250-duart.c b/drivers/tty/serial/sb1250-duart.c
index 771f361..041625c 100644
--- a/drivers/tty/serial/sb1250-duart.c
+++ b/drivers/tty/serial/sb1250-duart.c
@@ -41,7 +41,7 @@
#include <linux/tty_flip.h>
#include <linux/types.h>

-#include <linux/atomic.h>
+#include <linux/refcount.h>
#include <asm/io.h>
#include <asm/war.h>

@@ -103,7 +103,7 @@ struct sbd_port {
struct sbd_duart {
struct sbd_port sport[2];
unsigned long mapctrl;
- atomic_t map_guard;
+ refcount_t map_guard;
};

#define to_sport(uport) container_of(uport, struct sbd_port, port)
@@ -654,15 +654,13 @@ static void sbd_release_port(struct uart_port *uport)
{
struct sbd_port *sport = to_sport(uport);
struct sbd_duart *duart = sport->duart;
- int map_guard;

iounmap(sport->memctrl);
sport->memctrl = NULL;
iounmap(uport->membase);
uport->membase = NULL;

- map_guard = atomic_add_return(-1, &duart->map_guard);
- if (!map_guard)
+ if(refcount_dec_and_test(&duart->map_guard))
release_mem_region(duart->mapctrl, DUART_CHANREG_SPACING);
release_mem_region(uport->mapbase, DUART_CHANREG_SPACING);
}
@@ -698,7 +696,6 @@ static int sbd_request_port(struct uart_port *uport)
{
const char *err = KERN_ERR "sbd: Unable to reserve MMIO resource\n";
struct sbd_duart *duart = to_sport(uport)->duart;
- int map_guard;
int ret = 0;

if (!request_mem_region(uport->mapbase, DUART_CHANREG_SPACING,
@@ -706,11 +703,11 @@ static int sbd_request_port(struct uart_port *uport)
printk(err);
return -EBUSY;
}
- map_guard = atomic_add_return(1, &duart->map_guard);
- if (map_guard == 1) {
+ refcount_inc(&duart->map_guard);
+ if (refcount_read(&duart->map_guard) == 1) {
if (!request_mem_region(duart->mapctrl, DUART_CHANREG_SPACING,
"sb1250-duart")) {
- atomic_add(-1, &duart->map_guard);
+ refcount_dec(&duart->map_guard);
printk(err);
ret = -EBUSY;
}
@@ -718,8 +715,7 @@ static int sbd_request_port(struct uart_port *uport)
if (!ret) {
ret = sbd_map_port(uport);
if (ret) {
- map_guard = atomic_add_return(-1, &duart->map_guard);
- if (!map_guard)
+ if (refcount_dec_and_test(&duart->map_guard))
release_mem_region(duart->mapctrl,
DUART_CHANREG_SPACING);
}
--
2.7.4

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