[PATCH] usb: gadget: f_tcm: detach the gadget in usbg_drop_tpg() to fix a use-after-free

[Hui Peng <benquike@gmail.com>]

A target portal group can be removed with rmdir() on its configfs
directory while it is still enabled and still attached to a USB gadget
function. usbg_drop_tpg() frees the struct usbg_tpg but never calls
usbg_detach(), and it leaves opts->can_attach set, so the function
instance keeps a dangling tpg pointer and a subsequent bind to a UDC
happily attaches to freed memory.

Enumerating the gadget then dereferences the freed tpg from the UAS/BOT
completion path, in softirq context:

 ==================================================================
 BUG: KASAN: slab-use-after-free in usbg_submit_command.isra.0+0xbe7/0xd50
 Read of size 8 at addr ffff888107493478 by task swapper/3/0

 CPU: 3 UID: 0 PID: 0 Comm: swapper/3 Tainted: G    B D    7.3.0-rc3-g5dd1818b15d9 #1 PREEMPT(lazy)
 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996)
 Call Trace:
  <IRQ>
  dump_stack_lvl+0x70/0xa0
  print_report+0x153/0x4c6
  kasan_report+0xf1/0x120
  usbg_submit_command.isra.0+0xbe7/0xd50
  uasp_cmd_complete+0x83/0xf0
  dummy_timer+0x1337/0x2d60
  __hrtimer_run_queues+0x2a3/0x640
  hrtimer_run_softirq+0x1b1/0x3d0
  handle_softirqs+0x188/0x4e0
  __irq_exit_rcu+0x62/0x150
  sysvec_apic_timer_interrupt+0x6b/0x80
  </IRQ>

 Allocated by task 1:
  __kmalloc_cache_noprof+0x16a/0x380
  usbg_make_tpg+0x243/0x580
  target_fabric_make_tpg+0xb1/0x7f0
  configfs_mkdir+0x4e9/0xe10
  vfs_mkdir+0x2ed/0x790
  __x64_sys_mkdir+0x6f/0xa0

 Freed by task 1:
  kfree+0x159/0x420
  config_item_cleanup+0x148/0x1e0
  config_item_put+0x90/0xb0
  configfs_rmdir+0x816/0xa50
 ==================================================================

Detach the gadget in usbg_drop_tpg() if the tpg is still connected, and
clear opts->can_attach for every function instance bound to this tpg so
that a later usbg_attach() cannot pick up the freed object.

The forward declarations of usbg_attach() and usbg_detach() are moved
above usbg_drop_tpg() since it now calls usbg_detach().

Assisted-by: LLM
Signed-off-by: Hui Peng <benquike@gmail.com>
---
No Fixes: tag: I could not identify a single commit that introduced
the problem with confidence, so I have left it out rather than guess.

Reproduced on Linux 7.3.0-rc3 (5dd1818b15d9) with KASAN under QEMU using
dummy_hcd: create a tcm function and a target tpgt_1, write 1 to its
"enable" attribute, link the function into a gadget config, rmdir tpgt_1
without disabling it first, then bind the gadget to dummy_udc.0. With
this patch applied the same sequence produces no KASAN splat.

 drivers/usb/gadget/function/f_tcm.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

--- a/drivers/usb/gadget/function/f_tcm.c
+++ b/drivers/usb/gadget/function/f_tcm.c
@@ -1756,6 +1756,9 @@ unlock_inst:
 
 static int tcm_usbg_drop_nexus(struct usbg_tpg *);
 
+static int usbg_attach(struct usbg_tpg *);
+static void usbg_detach(struct usbg_tpg *);
+
 static void usbg_drop_tpg(struct se_portal_group *se_tpg)
 {
 	struct usbg_tpg *tpg = container_of(se_tpg,
@@ -1763,6 +1766,11 @@ static void usbg_drop_tpg(struct se_port
 	unsigned i;
 	struct f_tcm_opts *opts;
 
+	if (tpg->gadget_connect) {
+		usbg_detach(tpg);
+		tpg->gadget_connect = false;
+	}
+
 	tcm_usbg_drop_nexus(tpg);
 	core_tpg_deregister(se_tpg);
 	destroy_workqueue(tpg->workqueue);
@@ -1776,6 +1784,7 @@ static void usbg_drop_tpg(struct se_port
 		opts = container_of(tpg_instances[i].func_inst,
 			struct f_tcm_opts, func_inst);
 		mutex_lock(&opts->dep_lock);
+		opts->can_attach = false;
 		if (opts->has_dep)
 			module_put(opts->dependent);
 		else
@@ -1832,9 +1841,6 @@ static struct configfs_attribute *usbg_w
 	NULL,
 };
 
-static int usbg_attach(struct usbg_tpg *);
-static void usbg_detach(struct usbg_tpg *);
-
 static int usbg_enable_tpg(struct se_portal_group *se_tpg, bool enable)
 {
 	struct usbg_tpg  *tpg = container_of(se_tpg, struct usbg_tpg, se_tpg);
-- 
2.43.0