[PATCH] can: bcm: Fix UAF in bcm_proc_show()

[YueHaibing]

BUG: KASAN: slab-use-after-free in bcm_proc_show+0x969/0xa80
Read of size 8 at addr ffff888155846230 by task cat/7862

CPU: 1 PID: 7862 Comm: cat Not tainted 6.5.0-rc1-00153-gc8746099c197 #230
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0xd5/0x150
 print_report+0xc1/0x5e0
 kasan_report+0xba/0xf0
 bcm_proc_show+0x969/0xa80
 seq_read_iter+0x4f6/0x1260
 seq_read+0x165/0x210
 proc_reg_read+0x227/0x300
 vfs_read+0x1d5/0x8d0
 ksys_read+0x11e/0x240
 do_syscall_64+0x35/0xb0
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Allocated by task 7846:
 kasan_save_stack+0x1e/0x40
 kasan_set_track+0x21/0x30
 __kasan_kmalloc+0x9e/0xa0
 bcm_sendmsg+0x264b/0x44e0
 sock_sendmsg+0xda/0x180
 ____sys_sendmsg+0x735/0x920
 ___sys_sendmsg+0x11d/0x1b0
 __sys_sendmsg+0xfa/0x1d0
 do_syscall_64+0x35/0xb0
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Freed by task 7846:
 kasan_save_stack+0x1e/0x40
 kasan_set_track+0x21/0x30
 kasan_save_free_info+0x27/0x40
 ____kasan_slab_free+0x161/0x1c0
 slab_free_freelist_hook+0x119/0x220
 __kmem_cache_free+0xb4/0x2e0
 rcu_core+0x809/0x1bd0

bcm_op is freed before procfs entry be removed in bcm_release(),
this lead to bcm_proc_show() may read the freed bcm_op.

Fixes: ffd980f976e7 ("[CAN]: Add broadcast manager (bcm) protocol")
Signed-off-by: YueHaibing <yuehaibing@xxxxxxxxxx>
---
 net/can/bcm.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/net/can/bcm.c b/net/can/bcm.c
index 9ba35685b043..9168114fc87f 100644
--- a/net/can/bcm.c
+++ b/net/can/bcm.c
@@ -1526,6 +1526,12 @@ static int bcm_release(struct socket *sock)
 
 	lock_sock(sk);
 
+#if IS_ENABLED(CONFIG_PROC_FS)
+	/* remove procfs entry */
+	if (net->can.bcmproc_dir && bo->bcm_proc_read)
+		remove_proc_entry(bo->procname, net->can.bcmproc_dir);
+#endif /* CONFIG_PROC_FS */
+
 	list_for_each_entry_safe(op, next, &bo->tx_ops, list)
 		bcm_remove_op(op);
 
@@ -1561,12 +1567,6 @@ static int bcm_release(struct socket *sock)
 	list_for_each_entry_safe(op, next, &bo->rx_ops, list)
 		bcm_remove_op(op);
 
-#if IS_ENABLED(CONFIG_PROC_FS)
-	/* remove procfs entry */
-	if (net->can.bcmproc_dir && bo->bcm_proc_read)
-		remove_proc_entry(bo->procname, net->can.bcmproc_dir);
-#endif /* CONFIG_PROC_FS */
-
 	/* remove device reference */
 	if (bo->bound) {
 		bo->bound   = 0;
-- 
2.34.1