bpf: Make use of probe_user_write in probe write helper

Convert the bpf_probe_write_user() helper to probe_user_write() such that
writes are not attempted under KERNEL_DS anymore which is buggy as kernel
and user space pointers can have overlapping addresses. Also, given we have
the access_ok() check inside probe_user_write(), the helper doesn't need
to do it twice.

Fixes: 96ae52279594 ("bpf: Add bpf_probe_write_user BPF helper to be called in tracers")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/841c461781874c07a0ee404a454c3bc0459eed30.1572649915.git.daniel@iogearbox.net

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index f50bf19f7a05d3389f964b764805c8e445f1e12b..2d87fcdcb19bb8f116d0455c4a86282e3c82ee00 100644 (file)
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -163,7 +163,7 @@ static const struct bpf_func_proto bpf_probe_read_proto = {
        .arg3_type      = ARG_ANYTHING,
 };
 
-BPF_CALL_3(bpf_probe_write_user, void *, unsafe_ptr, const void *, src,
+BPF_CALL_3(bpf_probe_write_user, void __user *, unsafe_ptr, const void *, src,
           u32, size)
 {
        /*
@@ -186,10 +186,8 @@ BPF_CALL_3(bpf_probe_write_user, void *, unsafe_ptr, const void *, src,
                return -EPERM;
        if (unlikely(!nmi_uaccess_okay()))
                return -EPERM;
-       if (!access_ok(unsafe_ptr, size))
-               return -EPERM;
 
-       return probe_kernel_write(unsafe_ptr, src, size);
+       return probe_user_write(unsafe_ptr, src, size);
 }
 
 static const struct bpf_func_proto bpf_probe_write_user_proto = {