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From:   Sven Schnelle <svens@linux.ibm.com>
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     linux-kernel@vger.kernel.org
Subject: [PATCH] tracing: fix memcpy size when copying stack entries
Date:   Mon, 12 Jun 2023 18:07:48 +0200
Message-Id: <20230612160748.4082850-1-svens@linux.ibm.com>
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Noticed the following warning during boot:

[    2.316341] Testing tracer wakeup:
[    2.383512] ------------[ cut here ]------------
[    2.383517] memcpy: detected field-spanning write (size 104) of single field "&entry->caller" at kernel/trace/trace.c:3167 (size 64)

The reason seems to be that the maximum number of entries is calculated
from the size of the fstack->calls array which is 128. But later the same
size is used to memcpy() the entries to entry->callers, which has only
room for eight elements. Therefore use the minimum of both arrays as limit.

Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
---
 kernel/trace/trace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 64a4dde073ef..988d664c13ec 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3146,7 +3146,7 @@ static void __ftrace_trace_stack(struct trace_buffer *buffer,
 	barrier();
 
 	fstack = this_cpu_ptr(ftrace_stacks.stacks) + stackidx;
-	size = ARRAY_SIZE(fstack->calls);
+	size = min(ARRAY_SIZE(entry->caller), ARRAY_SIZE(fstack->calls));
 
 	if (regs) {
 		nr_entries = stack_trace_save_regs(regs, fstack->calls,
-- 
2.39.2