@@ -158,11 +158,14 @@ static void unix_add_edge(struct scm_fp_list *fpl, struct unix_edge *edge)
unix_update_graph(unix_edge_successor(edge));
}
+static bool gc_in_progress;
+
static void unix_del_edge(struct scm_fp_list *fpl, struct unix_edge *edge)
{
struct unix_vertex *vertex = edge->predecessor->vertex;
- unix_update_graph(unix_edge_successor(edge));
+ if (!gc_in_progress)
+ unix_update_graph(unix_edge_successor(edge));
list_del(&edge->vertex_entry);
vertex->out_degree--;
@@ -237,8 +240,10 @@ void unix_del_edges(struct scm_fp_list *fpl)
unix_del_edge(fpl, edge);
} while (i < fpl->count_unix);
- receiver = fpl->edges[0].successor;
- receiver->scm_stat.nr_unix_fds -= fpl->count_unix;
+ if (!gc_in_progress) {
+ receiver = fpl->edges[0].successor;
+ receiver->scm_stat.nr_unix_fds -= fpl->count_unix;
+ }
WRITE_ONCE(unix_tot_inflight, unix_tot_inflight - fpl->count_unix);
out:
WRITE_ONCE(fpl->user->unix_inflight, fpl->user->unix_inflight - fpl->count);
@@ -526,6 +531,8 @@ static void unix_walk_scc(struct sk_buff_head *hitlist)
static void unix_walk_scc_fast(struct sk_buff_head *hitlist)
{
+ unix_graph_maybe_cyclic = false;
+
while (!list_empty(&unix_unvisited_vertices)) {
struct unix_vertex *vertex;
struct list_head scc;
@@ -543,6 +550,8 @@ static void unix_walk_scc_fast(struct sk_buff_head *hitlist)
if (scc_dead)
unix_collect_skb(&scc, hitlist);
+ else if (!unix_graph_maybe_cyclic)
+ unix_graph_maybe_cyclic = unix_scc_cyclic(&scc);
list_del(&scc);
}
@@ -550,8 +559,6 @@ static void unix_walk_scc_fast(struct sk_buff_head *hitlist)
list_replace_init(&unix_visited_vertices, &unix_unvisited_vertices);
}
-static bool gc_in_progress;
-
static void __unix_gc(struct work_struct *work)
{
struct sk_buff_head hitlist;
syzbot reported use-after-free in unix_del_edges(). [0] What the repro does is basically repeat the following quickly. 1. pass a fd of an AF_UNIX socket to itself socketpair(AF_UNIX, SOCK_DGRAM, 0, [3, 4]) = 0 sendmsg(3, {..., msg_control=[{cmsg_len=20, cmsg_level=SOL_SOCKET, cmsg_type=SCM_RIGHTS, cmsg_data=[4]}], ...}, 0) = 0 2. pass other fds of AF_UNIX sockets to the socket above socketpair(AF_UNIX, SOCK_SEQPACKET, 0, [5, 6]) = 0 sendmsg(3, {..., msg_control=[{cmsg_len=48, cmsg_level=SOL_SOCKET, cmsg_type=SCM_RIGHTS, cmsg_data=[5, 6]}], ...}, 0) = 0 3. close all sockets Here, two skb are created, and every unix_edge->successor is the first socket. Then, __unix_gc() will garbage-collect the two skb: (a) free skb with self-referencing fd (b) free skb holding other sockets After (a), the self-referencing socket will be scheduled to be freed later by the delayed_fput() task. syzbot repeated the sequences above (1. ~ 3.) quickly and triggered the task concurrently while GC was running. So, at (b), the socket was already freed, and accessing it was illegal. unix_del_edges() accesses the receiver socket as edge->successor to optimise GC. However, we should not do it during GC. Garbage-collecting sockets does not change the shape of the rest of the graph, so we need not call unix_update_graph() to update unix_graph_grouped when we purge skb. However, if we clean up all loops in the unix_walk_scc_fast() path, unix_graph_maybe_cyclic remains unchanged (true), and __unix_gc() will call unix_walk_scc_fast() continuously even though there is no socket to garbage-collect. To keep that optimisation while fixing UAF, let's add the same updating logic of unix_graph_maybe_cyclic in unix_walk_scc_fast() as done in unix_walk_scc() and __unix_walk_scc(). Note that when unix_del_edges() is called from other places, the receiver socket is always alive: - sendmsg: the successor's sk_refcnt is bumped by sock_hold() unix_find_other() for SOCK_DGRAM, connect() for SOCK_STREAM - recvmsg: the successor is the receiver, and its fd is alive [0]: BUG: KASAN: slab-use-after-free in unix_edge_successor net/unix/garbage.c:109 [inline] BUG: KASAN: slab-use-after-free in unix_del_edge net/unix/garbage.c:165 [inline] BUG: KASAN: slab-use-after-free in unix_del_edges+0x148/0x630 net/unix/garbage.c:237 Read of size 8 at addr ffff888079c6e640 by task kworker/u8:6/1099 CPU: 0 PID: 1099 Comm: kworker/u8:6 Not tainted 6.9.0-rc4-next-20240418-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024 Workqueue: events_unbound __unix_gc Call Trace: <TASK> __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114 print_address_description mm/kasan/report.c:377 [inline] print_report+0x169/0x550 mm/kasan/report.c:488 kasan_report+0x143/0x180 mm/kasan/report.c:601 unix_edge_successor net/unix/garbage.c:109 [inline] unix_del_edge net/unix/garbage.c:165 [inline] unix_del_edges+0x148/0x630 net/unix/garbage.c:237 unix_destroy_fpl+0x59/0x210 net/unix/garbage.c:298 unix_detach_fds net/unix/af_unix.c:1811 [inline] unix_destruct_scm+0x13e/0x210 net/unix/af_unix.c:1826 skb_release_head_state+0x100/0x250 net/core/skbuff.c:1127 skb_release_all net/core/skbuff.c:1138 [inline] __kfree_skb net/core/skbuff.c:1154 [inline] kfree_skb_reason+0x16d/0x3b0 net/core/skbuff.c:1190 __skb_queue_purge_reason include/linux/skbuff.h:3251 [inline] __skb_queue_purge include/linux/skbuff.h:3256 [inline] __unix_gc+0x1732/0x1830 net/unix/garbage.c:575 process_one_work kernel/workqueue.c:3218 [inline] process_scheduled_works+0xa2c/0x1830 kernel/workqueue.c:3299 worker_thread+0x86d/0xd70 kernel/workqueue.c:3380 kthread+0x2f0/0x390 kernel/kthread.c:389 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244 </TASK> Allocated by task 14427: kasan_save_stack mm/kasan/common.c:47 [inline] kasan_save_track+0x3f/0x80 mm/kasan/common.c:68 unpoison_slab_object mm/kasan/common.c:312 [inline] __kasan_slab_alloc+0x66/0x80 mm/kasan/common.c:338 kasan_slab_alloc include/linux/kasan.h:201 [inline] slab_post_alloc_hook mm/slub.c:3897 [inline] slab_alloc_node mm/slub.c:3957 [inline] kmem_cache_alloc_noprof+0x135/0x290 mm/slub.c:3964 sk_prot_alloc+0x58/0x210 net/core/sock.c:2074 sk_alloc+0x38/0x370 net/core/sock.c:2133 unix_create1+0xb4/0x770 unix_create+0x14e/0x200 net/unix/af_unix.c:1034 __sock_create+0x490/0x920 net/socket.c:1571 sock_create net/socket.c:1622 [inline] __sys_socketpair+0x33e/0x720 net/socket.c:1773 __do_sys_socketpair net/socket.c:1822 [inline] __se_sys_socketpair net/socket.c:1819 [inline] __x64_sys_socketpair+0x9b/0xb0 net/socket.c:1819 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f Freed by task 1805: kasan_save_stack mm/kasan/common.c:47 [inline] kasan_save_track+0x3f/0x80 mm/kasan/common.c:68 kasan_save_free_info+0x40/0x50 mm/kasan/generic.c:579 poison_slab_object+0xe0/0x150 mm/kasan/common.c:240 __kasan_slab_free+0x37/0x60 mm/kasan/common.c:256 kasan_slab_free include/linux/kasan.h:184 [inline] slab_free_hook mm/slub.c:2190 [inline] slab_free mm/slub.c:4393 [inline] kmem_cache_free+0x145/0x340 mm/slub.c:4468 sk_prot_free net/core/sock.c:2114 [inline] __sk_destruct+0x467/0x5f0 net/core/sock.c:2208 sock_put include/net/sock.h:1948 [inline] unix_release_sock+0xa8b/0xd20 net/unix/af_unix.c:665 unix_release+0x91/0xc0 net/unix/af_unix.c:1049 __sock_release net/socket.c:659 [inline] sock_close+0xbc/0x240 net/socket.c:1421 __fput+0x406/0x8b0 fs/file_table.c:422 delayed_fput+0x59/0x80 fs/file_table.c:445 process_one_work kernel/workqueue.c:3218 [inline] process_scheduled_works+0xa2c/0x1830 kernel/workqueue.c:3299 worker_thread+0x86d/0xd70 kernel/workqueue.c:3380 kthread+0x2f0/0x390 kernel/kthread.c:389 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244 The buggy address belongs to the object at ffff888079c6e000 which belongs to the cache UNIX of size 1920 The buggy address is located 1600 bytes inside of freed 1920-byte region [ffff888079c6e000, ffff888079c6e780) Reported-by: syzbot+f3f3eef1d2100200e593@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=f3f3eef1d2100200e593 Fixes: 77e5593aebba ("af_unix: Skip GC if no cycle exists.") Fixes: fd86344823b5 ("af_unix: Try not to hold unix_gc_lock during accept().") Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com> --- net/unix/garbage.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-)