bpf/tracing: fix a deadlock in perf_event_detach_bpf_prog
syzbot reported a possible deadlock in perf_event_detach_bpf_prog. The error details: ====================================================== WARNING: possible circular locking dependency detected 4.16.0-rc7+ #3 Not tainted ------------------------------------------------------ syz-executor7/24531 is trying to acquire lock: (bpf_event_mutex){+.+.}, at: [<000000008a849b07>] perf_event_detach_bpf_prog+0x92/0x3d0 kernel/trace/bpf_trace.c:854 but task is already holding lock: (&mm->mmap_sem){++++}, at: [<0000000038768f87>] vm_mmap_pgoff+0x198/0x280 mm/util.c:353 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (&mm->mmap_sem){++++}: __might_fault+0x13a/0x1d0 mm/memory.c:4571 _copy_to_user+0x2c/0xc0 lib/usercopy.c:25 copy_to_user include/linux/uaccess.h:155 [inline] bpf_prog_array_copy_info+0xf2/0x1c0 kernel/bpf/core.c:1694 perf_event_query_prog_array+0x1c7/0x2c0 kernel/trace/bpf_trace.c:891 _perf_ioctl kernel/events/core.c:4750 [inline] perf_ioctl+0x3e1/0x1480 kernel/events/core.c:4770 vfs_ioctl fs/ioctl.c:46 [inline] do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686 SYSC_ioctl fs/ioctl.c:701 [inline] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692 do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287 entry_SYSCALL_64_after_hwframe+0x42/0xb7 -> #0 (bpf_event_mutex){+.+.}: lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:3920 __mutex_lock_common kernel/locking/mutex.c:756 [inline] __mutex_lock+0x16f/0x1a80 kernel/locking/mutex.c:893 mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908 perf_event_detach_bpf_prog+0x92/0x3d0 kernel/trace/bpf_trace.c:854 perf_event_free_bpf_prog kernel/events/core.c:8147 [inline] _free_event+0xbdb/0x10f0 kernel/events/core.c:4116 put_event+0x24/0x30 kernel/events/core.c:4204 perf_mmap_close+0x60d/0x1010 kernel/events/core.c:5172 remove_vma+0xb4/0x1b0 mm/mmap.c:172 remove_vma_list mm/mmap.c:2490 [inline] do_munmap+0x82a/0xdf0 mm/mmap.c:2731 mmap_region+0x59e/0x15a0 mm/mmap.c:1646 do_mmap+0x6c0/0xe00 mm/mmap.c:1483 do_mmap_pgoff include/linux/mm.h:2223 [inline] vm_mmap_pgoff+0x1de/0x280 mm/util.c:355 SYSC_mmap_pgoff mm/mmap.c:1533 [inline] SyS_mmap_pgoff+0x462/0x5f0 mm/mmap.c:1491 SYSC_mmap arch/x86/kernel/sys_x86_64.c:100 [inline] SyS_mmap+0x16/0x20 arch/x86/kernel/sys_x86_64.c:91 do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287 entry_SYSCALL_64_after_hwframe+0x42/0xb7 other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&mm->mmap_sem); lock(bpf_event_mutex); lock(&mm->mmap_sem); lock(bpf_event_mutex); *** DEADLOCK *** ====================================================== The bug is introduced by Commitf371b304f1
("bpf/tracing: allow user space to query prog array on the same tp") where copy_to_user, which requires mm->mmap_sem, is called inside bpf_event_mutex lock. At the same time, during perf_event file descriptor close, mm->mmap_sem is held first and then subsequent perf_event_detach_bpf_prog needs bpf_event_mutex lock. Such a senario caused a deadlock. As suggested by Daniel, moving copy_to_user out of the bpf_event_mutex lock should fix the problem. Fixes:f371b304f1
("bpf/tracing: allow user space to query prog array on the same tp") Reported-by: syzbot+dc5ca0e4c9bfafaf2bae@syzkaller.appspotmail.com Signed-off-by: Yonghong Song <yhs@fb.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
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@ -339,8 +339,8 @@ int bpf_prog_array_copy_to_user(struct bpf_prog_array __rcu *progs,
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void bpf_prog_array_delete_safe(struct bpf_prog_array __rcu *progs,
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struct bpf_prog *old_prog);
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int bpf_prog_array_copy_info(struct bpf_prog_array __rcu *array,
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__u32 __user *prog_ids, u32 request_cnt,
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__u32 __user *prog_cnt);
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u32 *prog_ids, u32 request_cnt,
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u32 *prog_cnt);
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int bpf_prog_array_copy(struct bpf_prog_array __rcu *old_array,
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struct bpf_prog *exclude_prog,
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struct bpf_prog *include_prog,
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@ -1572,13 +1572,32 @@ int bpf_prog_array_length(struct bpf_prog_array __rcu *progs)
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return cnt;
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}
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static bool bpf_prog_array_copy_core(struct bpf_prog **prog,
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u32 *prog_ids,
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u32 request_cnt)
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{
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int i = 0;
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for (; *prog; prog++) {
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if (*prog == &dummy_bpf_prog.prog)
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continue;
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prog_ids[i] = (*prog)->aux->id;
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if (++i == request_cnt) {
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prog++;
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break;
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}
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}
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return !!(*prog);
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}
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int bpf_prog_array_copy_to_user(struct bpf_prog_array __rcu *progs,
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__u32 __user *prog_ids, u32 cnt)
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{
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struct bpf_prog **prog;
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unsigned long err = 0;
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u32 i = 0, *ids;
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bool nospc;
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u32 *ids;
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/* users of this function are doing:
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* cnt = bpf_prog_array_length();
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@ -1595,16 +1614,7 @@ int bpf_prog_array_copy_to_user(struct bpf_prog_array __rcu *progs,
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return -ENOMEM;
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rcu_read_lock();
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prog = rcu_dereference(progs)->progs;
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for (; *prog; prog++) {
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if (*prog == &dummy_bpf_prog.prog)
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continue;
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ids[i] = (*prog)->aux->id;
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if (++i == cnt) {
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prog++;
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break;
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}
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}
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nospc = !!(*prog);
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nospc = bpf_prog_array_copy_core(prog, ids, cnt);
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rcu_read_unlock();
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err = copy_to_user(prog_ids, ids, cnt * sizeof(u32));
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kfree(ids);
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@ -1683,22 +1693,25 @@ int bpf_prog_array_copy(struct bpf_prog_array __rcu *old_array,
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}
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int bpf_prog_array_copy_info(struct bpf_prog_array __rcu *array,
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__u32 __user *prog_ids, u32 request_cnt,
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__u32 __user *prog_cnt)
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u32 *prog_ids, u32 request_cnt,
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u32 *prog_cnt)
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{
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struct bpf_prog **prog;
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u32 cnt = 0;
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if (array)
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cnt = bpf_prog_array_length(array);
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if (copy_to_user(prog_cnt, &cnt, sizeof(cnt)))
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return -EFAULT;
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*prog_cnt = cnt;
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/* return early if user requested only program count or nothing to copy */
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if (!request_cnt || !cnt)
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return 0;
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return bpf_prog_array_copy_to_user(array, prog_ids, request_cnt);
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/* this function is called under trace/bpf_trace.c: bpf_event_mutex */
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prog = rcu_dereference_check(array, 1)->progs;
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return bpf_prog_array_copy_core(prog, prog_ids, request_cnt) ? -ENOSPC
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: 0;
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}
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static void bpf_prog_free_deferred(struct work_struct *work)
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@ -977,6 +977,7 @@ int perf_event_query_prog_array(struct perf_event *event, void __user *info)
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{
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struct perf_event_query_bpf __user *uquery = info;
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struct perf_event_query_bpf query = {};
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u32 *ids, prog_cnt, ids_len;
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int ret;
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if (!capable(CAP_SYS_ADMIN))
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@ -985,16 +986,32 @@ int perf_event_query_prog_array(struct perf_event *event, void __user *info)
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return -EINVAL;
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if (copy_from_user(&query, uquery, sizeof(query)))
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return -EFAULT;
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if (query.ids_len > BPF_TRACE_MAX_PROGS)
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ids_len = query.ids_len;
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if (ids_len > BPF_TRACE_MAX_PROGS)
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return -E2BIG;
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ids = kcalloc(ids_len, sizeof(u32), GFP_USER | __GFP_NOWARN);
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if (!ids)
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return -ENOMEM;
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/*
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* The above kcalloc returns ZERO_SIZE_PTR when ids_len = 0, which
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* is required when user only wants to check for uquery->prog_cnt.
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* There is no need to check for it since the case is handled
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* gracefully in bpf_prog_array_copy_info.
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*/
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mutex_lock(&bpf_event_mutex);
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ret = bpf_prog_array_copy_info(event->tp_event->prog_array,
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uquery->ids,
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query.ids_len,
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&uquery->prog_cnt);
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ids,
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ids_len,
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&prog_cnt);
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mutex_unlock(&bpf_event_mutex);
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if (copy_to_user(&uquery->prog_cnt, &prog_cnt, sizeof(prog_cnt)) ||
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copy_to_user(uquery->ids, ids, ids_len * sizeof(u32)))
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ret = -EFAULT;
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kfree(ids);
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return ret;
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}
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