netdev - [PATCH bpf-next v3 3/8] bpf: Make use of probe_user

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Message-Id: <841c461781874c07a0ee404a454c3bc0459eed30.1572649915.git.daniel@iogearbox.net>
Date:   Sat,  2 Nov 2019 00:17:58 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     bpf@...r.kernel.org
Cc:     netdev@...r.kernel.org, ast@...nel.org, andrii.nakryiko@...il.com,
        john.fastabend@...il.com, Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andriin@...com>
Subject: [PATCH bpf-next v3 3/8] 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@...earbox.net>
Acked-by: Andrii Nakryiko <andriin@...com>
---
 kernel/trace/bpf_trace.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 571c25d60710..91eb17ac4bb6 100644
--- 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 = {
-- 
2.21.0