[PATCH 5.4 078/203] bpf: Make use of probe_user_write in probe write helper

Greg Kroah-Hartman
2020-01-16T23:22:24Z

From: Daniel Borkmann <daniel@iogearbox.net>

commit eb1b66887472eaa7342305b7890ae510dd9d1a79 upstream.

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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
kernel/trace/bpf_trace.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)

--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -163,7 +163,7 @@ static const struct bpf_func_proto bpf_p
.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 *,
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 = {