bpf: fix bpf_prog_array_copy_to_user() issues

1. move copy_to_user out of rcu section to fix the following issue:

./include/linux/rcupdate.h:302 Illegal context switch in RCU read-side critical section!
stack backtrace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:53
 lockdep_rcu_suspicious+0x123/0x170 kernel/locking/lockdep.c:4592
 rcu_preempt_sleep_check include/linux/rcupdate.h:301 [inline]
 ___might_sleep+0x385/0x470 kernel/sched/core.c:6079
 __might_sleep+0x95/0x190 kernel/sched/core.c:6067
 __might_fault+0xab/0x1d0 mm/memory.c:4532
 _copy_to_user+0x2c/0xc0 lib/usercopy.c:25
 copy_to_user include/linux/uaccess.h:155 [inline]
 bpf_prog_array_copy_to_user+0x217/0x4d0 kernel/bpf/core.c:1587
 bpf_prog_array_copy_info+0x17b/0x1c0 kernel/bpf/core.c:1685
 perf_event_query_prog_array+0x196/0x280 kernel/trace/bpf_trace.c:877
 _perf_ioctl kernel/events/core.c:4737 [inline]
 perf_ioctl+0x3e1/0x1480 kernel/events/core.c:4757

2. move *prog under rcu, since it's not ok to dereference it afterwards

3. in a rare case of prog array being swapped between bpf_prog_array_length()
   and bpf_prog_array_copy_to_user() calls make sure to copy zeros to user space,
   so the user doesn't walk over uninited prog_ids while kernel reported
   uattr->query.prog_cnt > 0

Reported-by: syzbot+7dbcd2d3b85f9b608b23@syzkaller.appspotmail.com
Fixes: 468e2f64d220 ("bpf: introduce BPF_PROG_QUERY command")
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 5f35f93..29ca920 100644 (file)
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1576,25 +1576,41 @@ int bpf_prog_array_copy_to_user(struct bpf_prog_array __rcu *progs,
                                __u32 __user *prog_ids, u32 cnt)
 {
        struct bpf_prog **prog;
-       u32 i = 0, id;
-
+       unsigned long err = 0;
+       u32 i = 0, *ids;
+       bool nospc;
+
+       /* users of this function are doing:
+        * cnt = bpf_prog_array_length();
+        * if (cnt > 0)
+        *     bpf_prog_array_copy_to_user(..., cnt);
+        * so below kcalloc doesn't need extra cnt > 0 check, but
+        * bpf_prog_array_length() releases rcu lock and
+        * prog array could have been swapped with empty or larger array,
+        * so always copy 'cnt' prog_ids to the user.
+        * In a rare race the user will see zero prog_ids
+        */
+       ids = kcalloc(cnt, sizeof(u32), GFP_USER);
+       if (!ids)
+               return -ENOMEM;
        rcu_read_lock();
        prog = rcu_dereference(progs)->progs;
        for (; *prog; prog++) {
                if (*prog == &dummy_bpf_prog.prog)
                        continue;
-               id = (*prog)->aux->id;
-               if (copy_to_user(prog_ids + i, &id, sizeof(id))) {
-                       rcu_read_unlock();
-                       return -EFAULT;
-               }
+               ids[i] = (*prog)->aux->id;
                if (++i == cnt) {
                        prog++;
                        break;
                }
        }
+       nospc = !!(*prog);
        rcu_read_unlock();
-       if (*prog)
+       err = copy_to_user(prog_ids, ids, cnt * sizeof(u32));
+       kfree(ids);
+       if (err)
+               return -EFAULT;
+       if (nospc)
                return -ENOSPC;
        return 0;
 }