netdev - [PATCH bpf] bpf: fix bpf_prog_array_copy_to_user warning from perf event prog query

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Message-Id: <20180214143100.18352-1-daniel@iogearbox.net>
Date:   Wed, 14 Feb 2018 15:31:00 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     ast@...nel.org
Cc:     yhs@...com, netdev@...r.kernel.org,
        Daniel Borkmann <daniel@...earbox.net>
Subject: [PATCH bpf] bpf: fix bpf_prog_array_copy_to_user warning from perf event prog query

syzkaller tried to perform a prog query in perf_event_query_prog_array()
where struct perf_event_query_bpf had an ids_len of 1,073,741,353 and
thus causing a warning due to failed kcalloc() allocation out of the
bpf_prog_array_copy_to_user() helper. Given we cannot attach more than
64 programs to a perf event, there's no point in allowing huge ids_len.
Therefore, allow a buffer that would fix the maximum number of ids and
also add a __GFP_NOWARN to the temporary ids buffer.

Fixes: f371b304f12e ("bpf/tracing: allow user space to query prog array on the same tp")
Fixes: 0911287ce32b ("bpf: fix bpf_prog_array_copy_to_user() issues")
Reported-by: syzbot+cab5816b0edbabf598b3@...kaller.appspotmail.com
Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
---
 kernel/bpf/core.c        | 2 +-
 kernel/trace/bpf_trace.c | 2 ++
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 29ca920..d315b39 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1590,7 +1590,7 @@ int bpf_prog_array_copy_to_user(struct bpf_prog_array __rcu *progs,
 	 * 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);
+	ids = kcalloc(cnt, sizeof(u32), GFP_USER | __GFP_NOWARN);
 	if (!ids)
 		return -ENOMEM;
 	rcu_read_lock();
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index fc2838a..c0a9e31 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -872,6 +872,8 @@ int perf_event_query_prog_array(struct perf_event *event, void __user *info)
 		return -EINVAL;
 	if (copy_from_user(&query, uquery, sizeof(query)))
 		return -EFAULT;
+	if (query.ids_len > BPF_TRACE_MAX_PROGS)
+		return -E2BIG;
 
 	mutex_lock(&bpf_event_mutex);
 	ret = bpf_prog_array_copy_info(event->tp_event->prog_array,
-- 
2.9.5