usb: typec: altmodes/displayport: fix pin_assignment_show

Badhri Jagan Sridharan · gregkh · commit d8f28269dd4b · 2023-05-13T18:45:56.000+09:00
This patch fixes negative indexing of buf array in pin_assignment_show when get_current_pin_assignments returns 0 i.e. no compatible pin assignments are found. BUG: KASAN: use-after-free in pin_assignment_show+0x26c/0x33c ... Call trace: dump_backtrace+0x110/0x204 dump_stack_lvl+0x84/0xbc print_report+0x358/0x974 kasan_report+0x9c/0xfc __do_kernel_fault+0xd4/0x2d4 do_bad_area+0x48/0x168 do_tag_check_fault+0x24/0x38 do_mem_abort+0x6c/0x14c el1_abort+0x44/0x68 el1h_64_sync_handler+0x64/0xa4 el1h_64_sync+0x78/0x7c pin_assignment_show+0x26c/0x33c dev_attr_show+0x50/0xc0 Fixes: 0e3bb7d ("usb: typec: Add driver for DisplayPort alternate mode") Cc: stable@vger.kernel.org Signed-off-by: Badhri Jagan Sridharan <badhri@google.com> Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com> Link: https://lore.kernel.org/r/20230508214443.893436-1-badhri@google.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/usb/typec/altmodes/displayport.c b/drivers/usb/typec/altmodes/displayport.c
@@ -516,6 +516,10 @@ static ssize_t pin_assignment_show(struct device *dev,
 
 	mutex_unlock(&dp->lock);
 
+	/* get_current_pin_assignments can return 0 when no matching pin assignments are found */
+	if (len == 0)
+		len++;
+
 	buf[len - 1] = '\n';
 	return len;
 }

Original file line number	Diff line number	Diff line change
`@@ -516,6 +516,10 @@ static ssize_t pin_assignment_show(struct device *dev,`
`516`	`516`
`517`	`517`	`mutex_unlock(&dp->lock);`
`518`	`518`
	`519`	`+ /* get_current_pin_assignments can return 0 when no matching pin assignments are found */`
	`520`	`+ if (len == 0)`
	`521`	`+ len++;`
	`522`	`+`
`519`	`523`	`buf[len - 1] = '\n';`
`520`	`524`	`return len;`
`521`	`525`	`}`