5.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Kuniyuki Iwashima kuniyu@amazon.com
[ Upstream commit 807067bf014d4a3ae2cc55bd3de16f22a01eb580 ]
syzkaller reported UAF in kcm_release(). [0]
The scenario is
1. Thread A builds a skb with MSG_MORE and sets kcm->seq_skb.
2. Thread A resumes building skb from kcm->seq_skb but is blocked by sk_stream_wait_memory()
3. Thread B calls sendmsg() concurrently, finishes building kcm->seq_skb and puts the skb to the write queue
4. Thread A faces an error and finally frees skb that is already in the write queue
5. kcm_release() does double-free the skb in the write queue
When a thread is building a MSG_MORE skb, another thread must not touch it.
Let's add a per-sk mutex and serialise kcm_sendmsg().
[0]: BUG: KASAN: slab-use-after-free in __skb_unlink include/linux/skbuff.h:2366 [inline] BUG: KASAN: slab-use-after-free in __skb_dequeue include/linux/skbuff.h:2385 [inline] BUG: KASAN: slab-use-after-free in __skb_queue_purge_reason include/linux/skbuff.h:3175 [inline] BUG: KASAN: slab-use-after-free in __skb_queue_purge include/linux/skbuff.h:3181 [inline] BUG: KASAN: slab-use-after-free in kcm_release+0x170/0x4c8 net/kcm/kcmsock.c:1691 Read of size 8 at addr ffff0000ced0fc80 by task syz-executor329/6167
CPU: 1 PID: 6167 Comm: syz-executor329 Tainted: G B 6.8.0-rc5-syzkaller-g9abbc24128bc #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024 Call trace: dump_backtrace+0x1b8/0x1e4 arch/arm64/kernel/stacktrace.c:291 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:298 __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0xd0/0x124 lib/dump_stack.c:106 print_address_description mm/kasan/report.c:377 [inline] print_report+0x178/0x518 mm/kasan/report.c:488 kasan_report+0xd8/0x138 mm/kasan/report.c:601 __asan_report_load8_noabort+0x20/0x2c mm/kasan/report_generic.c:381 __skb_unlink include/linux/skbuff.h:2366 [inline] __skb_dequeue include/linux/skbuff.h:2385 [inline] __skb_queue_purge_reason include/linux/skbuff.h:3175 [inline] __skb_queue_purge include/linux/skbuff.h:3181 [inline] kcm_release+0x170/0x4c8 net/kcm/kcmsock.c:1691 __sock_release net/socket.c:659 [inline] sock_close+0xa4/0x1e8 net/socket.c:1421 __fput+0x30c/0x738 fs/file_table.c:376 ____fput+0x20/0x30 fs/file_table.c:404 task_work_run+0x230/0x2e0 kernel/task_work.c:180 exit_task_work include/linux/task_work.h:38 [inline] do_exit+0x618/0x1f64 kernel/exit.c:871 do_group_exit+0x194/0x22c kernel/exit.c:1020 get_signal+0x1500/0x15ec kernel/signal.c:2893 do_signal+0x23c/0x3b44 arch/arm64/kernel/signal.c:1249 do_notify_resume+0x74/0x1f4 arch/arm64/kernel/entry-common.c:148 exit_to_user_mode_prepare arch/arm64/kernel/entry-common.c:169 [inline] exit_to_user_mode arch/arm64/kernel/entry-common.c:178 [inline] el0_svc+0xac/0x168 arch/arm64/kernel/entry-common.c:713 el0t_64_sync_handler+0x84/0xfc arch/arm64/kernel/entry-common.c:730 el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:598
Allocated by task 6166: kasan_save_stack mm/kasan/common.c:47 [inline] kasan_save_track+0x40/0x78 mm/kasan/common.c:68 kasan_save_alloc_info+0x70/0x84 mm/kasan/generic.c:626 unpoison_slab_object mm/kasan/common.c:314 [inline] __kasan_slab_alloc+0x74/0x8c mm/kasan/common.c:340 kasan_slab_alloc include/linux/kasan.h:201 [inline] slab_post_alloc_hook mm/slub.c:3813 [inline] slab_alloc_node mm/slub.c:3860 [inline] kmem_cache_alloc_node+0x204/0x4c0 mm/slub.c:3903 __alloc_skb+0x19c/0x3d8 net/core/skbuff.c:641 alloc_skb include/linux/skbuff.h:1296 [inline] kcm_sendmsg+0x1d3c/0x2124 net/kcm/kcmsock.c:783 sock_sendmsg_nosec net/socket.c:730 [inline] __sock_sendmsg net/socket.c:745 [inline] sock_sendmsg+0x220/0x2c0 net/socket.c:768 splice_to_socket+0x7cc/0xd58 fs/splice.c:889 do_splice_from fs/splice.c:941 [inline] direct_splice_actor+0xec/0x1d8 fs/splice.c:1164 splice_direct_to_actor+0x438/0xa0c fs/splice.c:1108 do_splice_direct_actor fs/splice.c:1207 [inline] do_splice_direct+0x1e4/0x304 fs/splice.c:1233 do_sendfile+0x460/0xb3c fs/read_write.c:1295 __do_sys_sendfile64 fs/read_write.c:1362 [inline] __se_sys_sendfile64 fs/read_write.c:1348 [inline] __arm64_sys_sendfile64+0x160/0x3b4 fs/read_write.c:1348 __invoke_syscall arch/arm64/kernel/syscall.c:37 [inline] invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:51 el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:136 do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:155 el0_svc+0x54/0x168 arch/arm64/kernel/entry-common.c:712 el0t_64_sync_handler+0x84/0xfc arch/arm64/kernel/entry-common.c:730 el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:598
Freed by task 6167: kasan_save_stack mm/kasan/common.c:47 [inline] kasan_save_track+0x40/0x78 mm/kasan/common.c:68 kasan_save_free_info+0x5c/0x74 mm/kasan/generic.c:640 poison_slab_object+0x124/0x18c mm/kasan/common.c:241 __kasan_slab_free+0x3c/0x78 mm/kasan/common.c:257 kasan_slab_free include/linux/kasan.h:184 [inline] slab_free_hook mm/slub.c:2121 [inline] slab_free mm/slub.c:4299 [inline] kmem_cache_free+0x15c/0x3d4 mm/slub.c:4363 kfree_skbmem+0x10c/0x19c __kfree_skb net/core/skbuff.c:1109 [inline] kfree_skb_reason+0x240/0x6f4 net/core/skbuff.c:1144 kfree_skb include/linux/skbuff.h:1244 [inline] kcm_release+0x104/0x4c8 net/kcm/kcmsock.c:1685 __sock_release net/socket.c:659 [inline] sock_close+0xa4/0x1e8 net/socket.c:1421 __fput+0x30c/0x738 fs/file_table.c:376 ____fput+0x20/0x30 fs/file_table.c:404 task_work_run+0x230/0x2e0 kernel/task_work.c:180 exit_task_work include/linux/task_work.h:38 [inline] do_exit+0x618/0x1f64 kernel/exit.c:871 do_group_exit+0x194/0x22c kernel/exit.c:1020 get_signal+0x1500/0x15ec kernel/signal.c:2893 do_signal+0x23c/0x3b44 arch/arm64/kernel/signal.c:1249 do_notify_resume+0x74/0x1f4 arch/arm64/kernel/entry-common.c:148 exit_to_user_mode_prepare arch/arm64/kernel/entry-common.c:169 [inline] exit_to_user_mode arch/arm64/kernel/entry-common.c:178 [inline] el0_svc+0xac/0x168 arch/arm64/kernel/entry-common.c:713 el0t_64_sync_handler+0x84/0xfc arch/arm64/kernel/entry-common.c:730 el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:598
The buggy address belongs to the object at ffff0000ced0fc80 which belongs to the cache skbuff_head_cache of size 240 The buggy address is located 0 bytes inside of freed 240-byte region [ffff0000ced0fc80, ffff0000ced0fd70)
The buggy address belongs to the physical page: page:00000000d35f4ae4 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10ed0f flags: 0x5ffc00000000800(slab|node=0|zone=2|lastcpupid=0x7ff) page_type: 0xffffffff() raw: 05ffc00000000800 ffff0000c1cbf640 fffffdffc3423100 dead000000000004 raw: 0000000000000000 00000000000c000c 00000001ffffffff 0000000000000000 page dumped because: kasan: bad access detected
Memory state around the buggy address: ffff0000ced0fb80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff0000ced0fc00: fb fb fb fb fb fb fc fc fc fc fc fc fc fc fc fc
ffff0000ced0fc80: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^ ffff0000ced0fd00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fc fc ffff0000ced0fd80: fc fc fc fc fc fc fc fc fa fb fb fb fb fb fb fb
Fixes: ab7ac4eb9832 ("kcm: Kernel Connection Multiplexor module") Reported-by: syzbot+b72d86aa5df17ce74c60@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=b72d86aa5df17ce74c60 Tested-by: syzbot+b72d86aa5df17ce74c60@syzkaller.appspotmail.com Signed-off-by: Kuniyuki Iwashima kuniyu@amazon.com Reviewed-by: Eric Dumazet edumazet@google.com Link: https://patch.msgid.link/20240815220437.69511-1-kuniyu@amazon.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- include/net/kcm.h | 1 + net/kcm/kcmsock.c | 4 ++++ 2 files changed, 5 insertions(+)
diff --git a/include/net/kcm.h b/include/net/kcm.h index 2d704f8f49059..8e8252e08a9ce 100644 --- a/include/net/kcm.h +++ b/include/net/kcm.h @@ -70,6 +70,7 @@ struct kcm_sock { struct work_struct tx_work; struct list_head wait_psock_list; struct sk_buff *seq_skb; + struct mutex tx_mutex; u32 tx_stopped : 1;
/* Don't use bit fields here, these are set under different locks */ diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c index 920b0ebf1cb80..50dceed77ba66 100644 --- a/net/kcm/kcmsock.c +++ b/net/kcm/kcmsock.c @@ -913,6 +913,7 @@ static int kcm_sendmsg(struct socket *sock, struct msghdr *msg, size_t len) !(msg->msg_flags & MSG_MORE) : !!(msg->msg_flags & MSG_EOR); int err = -EPIPE;
+ mutex_lock(&kcm->tx_mutex); lock_sock(sk);
/* Per tcp_sendmsg this should be in poll */ @@ -1061,6 +1062,7 @@ static int kcm_sendmsg(struct socket *sock, struct msghdr *msg, size_t len) KCM_STATS_ADD(kcm->stats.tx_bytes, copied);
release_sock(sk); + mutex_unlock(&kcm->tx_mutex); return copied;
out_error: @@ -1086,6 +1088,7 @@ static int kcm_sendmsg(struct socket *sock, struct msghdr *msg, size_t len) sk->sk_write_space(sk);
release_sock(sk); + mutex_unlock(&kcm->tx_mutex); return err; }
@@ -1328,6 +1331,7 @@ static void init_kcm_sock(struct kcm_sock *kcm, struct kcm_mux *mux) spin_unlock_bh(&mux->lock);
INIT_WORK(&kcm->tx_work, kcm_tx_work); + mutex_init(&kcm->tx_mutex);
spin_lock_bh(&mux->rx_lock); kcm_rcv_ready(kcm);