linux-kernel - [PATCH AUTOSEL 6.4 07/26] bpf: drop unnecessary user-triggerable WARN

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Message-Id: <20230709151255.512931-7-sashal@kernel.org>
Date:   Sun,  9 Jul 2023 11:12:36 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Andrii Nakryiko <andrii@...nel.org>,
        syzbot+8b2a08dfbd25fd933d75@...kaller.appspotmail.com,
        Alexei Starovoitov <ast@...nel.org>,
        Sasha Levin <sashal@...nel.org>, daniel@...earbox.net,
        bpf@...r.kernel.org
Subject: [PATCH AUTOSEL 6.4 07/26] bpf: drop unnecessary user-triggerable WARN_ONCE in verifierl log

From: Andrii Nakryiko <andrii@...nel.org>

[ Upstream commit cff36398bd4c7d322d424433db437f3c3391c491 ]

It's trivial for user to trigger "verifier log line truncated" warning,
as verifier has a fixed-sized buffer of 1024 bytes (as of now), and there are at
least two pieces of user-provided information that can be output through
this buffer, and both can be arbitrarily sized by user:
  - BTF names;
  - BTF.ext source code lines strings.

Verifier log buffer should be properly sized for typical verifier state
output. But it's sort-of expected that this buffer won't be long enough
in some circumstances. So let's drop the check. In any case code will
work correctly, at worst truncating a part of a single line output.

Reported-by: syzbot+8b2a08dfbd25fd933d75@...kaller.appspotmail.com
Signed-off-by: Andrii Nakryiko <andrii@...nel.org>
Link: https://lore.kernel.org/r/20230516180409.3549088-1-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 kernel/bpf/log.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/kernel/bpf/log.c b/kernel/bpf/log.c
index 046ddff37a76d..850494423530e 100644
--- a/kernel/bpf/log.c
+++ b/kernel/bpf/log.c
@@ -62,9 +62,6 @@ void bpf_verifier_vlog(struct bpf_verifier_log *log, const char *fmt,
 
 	n = vscnprintf(log->kbuf, BPF_VERIFIER_TMP_LOG_SIZE, fmt, args);
 
-	WARN_ONCE(n >= BPF_VERIFIER_TMP_LOG_SIZE - 1,
-		  "verifier log line truncated - local buffer too short\n");
-
 	if (log->level == BPF_LOG_KERNEL) {
 		bool newline = n > 0 && log->kbuf[n - 1] == '\n';
 
-- 
2.39.2