Input: psmouse - fix data race in __ps2_command

The data race happens on ps2dev->cmdcnt and ps2dev->cmdbuf contents.
__ps2_command reads that data concurrently with the interrupt handler. As
the result, for example, if a response arrives just after the timeout,
__ps2_command can copy out garbage from ps2dev->cmdbuf but then see that
ps2dev->cmdcnt is 0 and return success.

Stop the interrupt handler with serio_pause_rx() before reading the
results.

The data race was found with KernelThreadSanitizer (KTSAN).

Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

1 files changed, 14 insertions, 8 deletions

diff --git a/drivers/input/serio/libps2.c b/drivers/input/serio/libps2.c
index 75516996db20..316f2c897101 100644
--- a/drivers/input/serio/libps2.c
+++ b/drivers/input/serio/libps2.c
@@ -212,12 +212,17 @@ int __ps2_command(struct ps2dev *ps2dev, unsigned char *param, int command)
          * time before the ACK arrives.
          */
         if (ps2_sendbyte(ps2dev, command & 0xff,
-                         command == PS2_CMD_RESET_BAT ? 1000 : 200))
-                goto out;
+                         command == PS2_CMD_RESET_BAT ? 1000 : 200)) {
+                serio_pause_rx(ps2dev->serio);
+                goto out_reset_flags;
+        }
 
-        for (i = 0; i < send; i++)
-                if (ps2_sendbyte(ps2dev, param[i], 200))
-                        goto out;
+        for (i = 0; i < send; i++) {
+                if (ps2_sendbyte(ps2dev, param[i], 200)) {
+                        serio_pause_rx(ps2dev->serio);
+                        goto out_reset_flags;
+                }
+        }
 
         /*
          * The reset command takes a long time to execute.
@@ -234,17 +239,18 @@ int __ps2_command(struct ps2dev *ps2dev, unsigned char *param, int command)
                                    !(ps2dev->flags & PS2_FLAG_CMD), timeout);
         }
 
+        serio_pause_rx(ps2dev->serio);
+
         if (param)
                 for (i = 0; i < receive; i++)
                         param[i] = ps2dev->cmdbuf[(receive - 1) - i];
 
         if (ps2dev->cmdcnt && (command != PS2_CMD_RESET_BAT || ps2dev->cmdcnt != 1))
-                goto out;
+                goto out_reset_flags;
 
         rc = 0;
 
- out:
-        serio_pause_rx(ps2dev->serio);
+ out_reset_flags:
         ps2dev->flags = 0;
         serio_continue_rx(ps2dev->serio);