In the Linux kernel, the following vulnerability has been resolved: nfc: llcp: Fix memleak in nfc_llcp_send_ui_frame(). syzbot reported various memory leaks related to NFC, struct nfc_llcp_sock, sk_buff, nfc_dev, etc. [0] The leading log hinted that nfc_llcp_send_ui_frame() failed to allocate skb due to sock_error(sk) being -ENXIO. ENXIO is set by nfc_llcp_socket_release() when struct nfc_llcp_local is destroyed by local_cleanup(). The problem is that there is no synchronisation between nfc_llcp_send_ui_frame() and local_cleanup(), and skb could be put into local->tx_queue after it was purged in local_cleanup(): CPU1 CPU2 ---- ---- nfc_llcp_send_ui_frame() local_cleanup() |- do { ' |- pdu = nfc_alloc_send_skb(..., &err) | . | |- nfc_llcp_socket_release(local, false, ENXIO); | |- skb_queue_purge(&local->tx_queue); | | ' | |- skb_queue_tail(&local->tx_queue, pdu); | ... | |- pdu = nfc_alloc_send_skb(..., &err) | ^._________________________________.' local_cleanup() is called for struct nfc_llcp_local only after nfc_llcp_remove_local() unlinks it from llcp_devices. If we hold local->tx_queue.lock then, we can synchronise the thread and nfc_llcp_send_ui_frame(). Let's do that and check list_empty(&local->list) before queuing skb to local->tx_queue in nfc_llcp_send_ui_frame(). [0]: [ 56.074943][ T6096] llcp: nfc_llcp_send_ui_frame: Could not allocate PDU (error=-6) [ 64.318868][ T5813] kmemleak: 6 new suspected memory leaks (see /sys/kernel/debug/kmemleak) BUG: memory leak unreferenced object 0xffff8881272f6800 (size 1024): comm "syz.0.17", pid 6096, jiffies 4294942766 hex dump (first 32 bytes): 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 27 00 03 40 00 00 00 00 00 00 00 00 00 00 00 00 '..@............ backtrace (crc da58d84d): kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline] slab_post_alloc_hook mm/slub.c:4979 [inline] slab_alloc_node mm/slub.c:5284 [inline] __do_kmalloc_node mm/slub.c:5645 [inline] __kmalloc_noprof+0x3e3/0x6b0 mm/slub.c:5658 kmalloc_noprof include/linux/slab.h:961 [inline] sk_prot_alloc+0x11a/0x1b0 net/core/sock.c:2239 sk_alloc+0x36/0x360 net/core/sock.c:2295 nfc_llcp_sock_alloc+0x37/0x130 net/nfc/llcp_sock.c:979 llcp_sock_create+0x71/0xd0 net/nfc/llcp_sock.c:1044 nfc_sock_create+0xc9/0xf0 net/nfc/af_nfc.c:31 __sock_create+0x1a9/0x340 net/socket.c:1605 sock_create net/socket.c:1663 [inline] __sys_socket_create net/socket.c:1700 [inline] __sys_socket+0xb9/0x1a0 net/socket.c:1747 __do_sys_socket net/socket.c:1761 [inline] __se_sys_socket net/socket.c:1759 [inline] __x64_sys_socket+0x1b/0x30 net/socket.c:1759 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xa4/0xfa0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f BUG: memory leak unreferenced object 0xffff88810fbd9800 (size 240): comm "syz.0.17", pid 6096, jiffies 4294942850 hex dump (first 32 bytes): 68 f0 ff 08 81 88 ff ff 68 f0 ff 08 81 88 ff ff h.......h....... 00 00 00 00 00 00 00 00 00 68 2f 27 81 88 ff ff .........h/'.... backtrace (crc 6cc652b1): kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline] slab_post_alloc_hook mm/slub.c:4979 [inline] slab_alloc_node mm/slub.c:5284 [inline] kmem_cache_alloc_node_noprof+0x36f/0x5e0 mm/slub.c:5336 __alloc_skb+0x203/0x240 net/core/skbuff.c:660 alloc_skb include/linux/skbuff.h:1383 [inline] alloc_skb_with_frags+0x69/0x3f0 net/core/sk ---truncated---