A socket container's node and socket must remain alive while the container is on sock_containers. The debugfs formatter reads sc_node and sc_sock under o2net_debug_lock without taking their references, but sc_kref_release() releases both before taking that lock to unlink the container. With CONFIG_DEBUG_FS enabled, a synchronous sender can retain its last socket-container reference after o2net_disconnect_node() has detached the connection and flushed o2net_wq. The caller runs outside that workqueue. After the sender removes its configfs dependency, node removal can proceed without waiting for the sender's final sc_put(): Sender (final sc_put) Configfs rmdir Debugfs reader -------------------- -------------- -------------- o2nm_undepend_item() Drop node item refs o2nm_node_put() [node can be freed] sc_seq_show() Lock debug lock Read sc_node->nd_name Unlock debug lock sc_node = NULL o2net_debug_del_sc() The earlier socket release has a similar window. The container is still selectable while its socket has been released and sc_sock has not yet been cleared: Sender (final sc_put) Debugfs reader -------------------- -------------- sock_release(sc->sc_sock) [socket can be freed] sc_seq_show() Lock debug lock Read sc_sock->sk fields Unlock debug lock sc_sock = NULL ... o2net_debug_del_sc() Move o2net_debug_del_sc() before releasing either resource. Unlinking under the existing debug lock waits for an active formatter to finish and prevents later readers from selecting the container. This covers both socket fields and node fields, including nd_num in the stats formatter. KASAN report as below: BUG: KASAN: slab-use-after-free in string+0x42b/0x470 Read of size 1 at addr ffff88810f56fc90 by task python3/506 CPU: 0 UID: 0 PID: 506 Comm: python3 Not tainted 7.3.0-rc4-next-20260921-pmb-ocfs2-functional-v1+ #1 PREEMPT(lazy) Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 Call Trace: dump_stack_lvl+0x93/0xd0 print_report+0xce/0x630 kasan_report+0xe0/0x110 string+0x42b/0x470 vsnprintf+0x330/0x1110 seq_printf+0x1a8/0x260 sc_seq_show+0x604/0x9f0 seq_read_iter+0x480/0x1110 seq_read+0x362/0x5a0 full_proxy_read+0x11f/0x180 vfs_read+0x1a0/0xc20 ksys_read+0x111/0x200 do_syscall_64+0x114/0x620 entry_SYSCALL_64_after_hwframe+0x77/0x7f (User register dump omitted.) Allocated by task 497: kasan_save_stack+0x33/0x60 kasan_save_track+0x14/0x30 __kasan_kmalloc+0xaa/0xb0 __kmalloc_cache_noprof+0x28d/0x610 o2nm_node_group_make_item+0xea/0x1a0 configfs_mkdir+0x762/0xca0 vfs_mkdir+0x399/0x7e0 filename_mkdirat+0x129/0x450 __x64_sys_mkdir+0x70/0xa0 do_syscall_64+0x114/0x620 entry_SYSCALL_64_after_hwframe+0x77/0x7f Freed by task 505: kasan_save_stack+0x33/0x60 kasan_save_track+0x14/0x30 kasan_save_free_info+0x3b/0x60 __kasan_slab_free+0x5f/0x80 kfree+0x308/0x580 config_item_cleanup+0x14b/0x230 config_item_put+0x79/0x90 sc_put+0x454/0x6e0 o2net_send_message_vec+0x63d/0x1560 o2net_send_message+0xa6/0xe0 validation_send_write+0x17f/0x1d0 full_proxy_write+0x11f/0x180 vfs_write+0x25a/0x1010 ksys_write+0x111/0x200 do_syscall_64+0x114/0x620 entry_SYSCALL_64_after_hwframe+0x77/0x7f The buggy address belongs to the object at ffff88810f56fc00 which belongs to the cache kmalloc-512 of size 512 The buggy address is located 144 bytes inside of freed 512-byte region [ffff88810f56fc00, ffff88810f56fe00) (Page and shadow-memory dumps omitted.) Fixes: 2309e9e040fe ("ocfs2/net: Add debug interface to o2net") Cc: Reviewed-by: Joseph Qi Signed-off-by: Cen Zhang Assisted-by: LLM --- Changes in v3: - Revise commit message as joseph suggested. Changes in v2: - Move o2net_debug_del_sc() before socket and node cleanup, as Joseph suggested. - Use the ocfs2/cluster title prefix and describe the races with sequence diagrams. - Add Cc: stable@vger.kernel.org. Link to v1: https://lore.kernel.org/r/pm-ocfs2-objects-candidate-0065-v4-f45e5cef38dd587b2cfd@gmail.com Link to v2: https://lore.kernel.org/r/pm-ocfs2-objects-candidate-0065-v6-3090153fd7cacb810214@gmail.com fs/ocfs2/cluster/tcp.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/fs/ocfs2/cluster/tcp.c b/fs/ocfs2/cluster/tcp.c index 8b3830b601ba6e5fe964bec970581b8e4ddbb5dd..0eaf2c4a6989ecad00f7a88a66a782b334647f21 100644 --- a/fs/ocfs2/cluster/tcp.c +++ b/fs/ocfs2/cluster/tcp.c @@ -393,6 +393,9 @@ static void sc_kref_release(struct kref *kref) sclog(sc, "releasing\n"); + /* Unlink before freeing anything the debugfs readers dereference. */ + o2net_debug_del_sc(sc); + if (sc->sc_sock) { sock_release(sc->sc_sock); sc->sc_sock = NULL; @@ -402,8 +405,6 @@ static void sc_kref_release(struct kref *kref) o2nm_node_put(sc->sc_node); sc->sc_node = NULL; - o2net_debug_del_sc(sc); - if (sc->sc_page) __free_page(sc->sc_page); kfree(sc);