From 38d26d89b31d0766d431471572cc9b007ca19c98 Mon Sep 17 00:00:00 2001
From: Florent Revest <revest@chromium.org>
Date: Tue, 27 Apr 2021 13:29:58 +0200
Subject: [PATCH] bpf: Lock bpf_trace_printk's tmp buf before it is written to
bpf_trace_printk uses a shared static buffer to hold strings before they
are printed. A recent refactoring moved the locking of that buffer after
it gets filled by mistake.
Fixes: d9c9e4db186a ("bpf: Factorize bpf_trace_printk and bpf_seq_printf")
Reported-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Florent Revest <revest@chromium.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210427112958.773132-1-revest@chromium.org
---
kernel/trace/bpf_trace.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 2a8bcdc927c7f..0e67d12a8f40f 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -391,13 +391,13 @@ BPF_CALL_5(bpf_trace_printk, char *, fmt, u32, fmt_size, u64, arg1,
if (ret < 0)
return ret;
+ raw_spin_lock_irqsave(&trace_printk_lock, flags);
ret = snprintf(buf, sizeof(buf), fmt, BPF_CAST_FMT_ARG(0, args, mod),
BPF_CAST_FMT_ARG(1, args, mod), BPF_CAST_FMT_ARG(2, args, mod));
/* snprintf() will not append null for zero-length strings */
if (ret == 0)
buf[0] = '\0';
- raw_spin_lock_irqsave(&trace_printk_lock, flags);
trace_bpf_trace_printk(buf);
raw_spin_unlock_irqrestore(&trace_printk_lock, flags);
--
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