CVE-2020-25669 (published 2021-05-26T12:15Z)

A vulnerability was found in the Linux Kernel where the function sunkbd_reinit having been scheduled by sunkbd_interrupt before sunkbd being freed. Though the dangling pointer is set to NULL in sunkbd_disconnect, there is still an alias in sunkbd_reinit causing Use After Free.

Severity: HIGH
CVSS v2 base score: 7.2 (AV:L/AC:L/Au:N/C:C/I:C/A:C)
CVSS v3 base score: 7.8, HIGH (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H)

Weakness information:
cwe_id: CWE-416
cwe_name: Use After Free
description: The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.
extended_description: 
             
             
             
			 
             
             
         
         

Fix information:
repo_url: https://github.com/torvalds/linux
commit_details: repo_url: https://github.com/torvalds/linux
author: Dmitry Torokhov
author_date: 2020-10-26 13:36:17-07:00
msg: Input: sunkbd - avoid use-after-free in teardown paths

We need to make sure we cancel the reinit work before we tear down the
driver structures.

Reported-by: Bodong Zhao <nopitydays@gmail.com>
Tested-by: Bodong Zhao <nopitydays@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
repository: repo_url: https://github.com/torvalds/linux
repo_name: torvalds/linux
description: Linux kernel source tree
repo_language: C
owner: torvalds
file_changes: filename: sunkbd.c
change_type: ModificationType.MODIFY
diff: @@ -99,7 +99,8 @@ static irqreturn_t sunkbd_interrupt(struct serio *serio,
 	switch (data) {
 
 	case SUNKBD_RET_RESET:
-		schedule_work(&sunkbd->tq);
+		if (sunkbd->enabled)
+			schedule_work(&sunkbd->tq);
 		sunkbd->reset = -1;
 		break;
 
@@ -200,16 +201,12 @@ static int sunkbd_initialize(struct sunkbd *sunkbd)
 }
 
 /*
- * sunkbd_reinit() sets leds and beeps to a state the computer remembers they
- * were in.
+ * sunkbd_set_leds_beeps() sets leds and beeps to a state the computer remembers
+ * they were in.
  */
 
-static void sunkbd_reinit(struct work_struct *work)
+static void sunkbd_set_leds_beeps(struct sunkbd *sunkbd)
 {
-	struct sunkbd *sunkbd = container_of(work, struct sunkbd, tq);
-
-	wait_event_interruptible_timeout(sunkbd->wait, sunkbd->reset >= 0, HZ);
-
 	serio_write(sunkbd->serio, SUNKBD_CMD_SETLED);
 	serio_write(sunkbd->serio,
 		(!!test_bit(LED_CAPSL,   sunkbd->dev->led) << 3) |
@@ -222,11 +219,39 @@ static void sunkbd_reinit(struct work_struct *work)
 		SUNKBD_CMD_BELLOFF - !!test_bit(SND_BELL, sunkbd->dev->snd));
 }
 
+
+/*
+ * sunkbd_reinit() wait for the keyboard reset to complete and restores state
+ * of leds and beeps.
+ */
+
+static void sunkbd_reinit(struct work_struct *work)
+{
+	struct sunkbd *sunkbd = container_of(work, struct sunkbd, tq);
+
+	/*
+	 * It is OK that we check sunkbd->enabled without pausing serio,
+	 * as we only want to catch true->false transition that will
+	 * happen once and we will be woken up for it.
+	 */
+	wait_event_interruptible_timeout(sunkbd->wait,
+					 sunkbd->reset >= 0 || !sunkbd->enabled,
+					 HZ);
+
+	if (sunkbd->reset >= 0 && sunkbd->enabled)
+		sunkbd_set_leds_beeps(sunkbd);
+}
+
 static void sunkbd_enable(struct sunkbd *sunkbd, bool enable)
 {
 	serio_pause_rx(sunkbd->serio);
 	sunkbd->enabled = enable;
 	serio_continue_rx(sunkbd->serio);
+
+	if (!enable) {
+		wake_up_interruptible(&sunkbd->wait);
+		cancel_work_sync(&sunkbd->tq);
+	}
 }
 
 /*

programming_language: C