linux-kernel - [PATCH AUTOSEL 6.6 03/58] bpftool: Fix undefined behavior in qsort(NULL, 0, ...)

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Message-ID: <20241004182503.3672477-3-sashal@kernel.org>
Date: Fri,  4 Oct 2024 14:23:36 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Kuan-Wei Chiu <visitorckw@...il.com>,
	Andrii Nakryiko <andrii@...nel.org>,
	Quentin Monnet <qmo@...nel.org>,
	Sasha Levin <sashal@...nel.org>,
	ast@...nel.org,
	daniel@...earbox.net,
	bpf@...r.kernel.org
Subject: [PATCH AUTOSEL 6.6 03/58] bpftool: Fix undefined behavior in qsort(NULL, 0, ...)

From: Kuan-Wei Chiu <visitorckw@...il.com>

[ Upstream commit f04e2ad394e2755d0bb2d858ecb5598718bf00d5 ]

When netfilter has no entry to display, qsort is called with
qsort(NULL, 0, ...). This results in undefined behavior, as UBSan
reports:

net.c:827:2: runtime error: null pointer passed as argument 1, which is declared to never be null

Although the C standard does not explicitly state whether calling qsort
with a NULL pointer when the size is 0 constitutes undefined behavior,
Section 7.1.4 of the C standard (Use of library functions) mentions:

"Each of the following statements applies unless explicitly stated
otherwise in the detailed descriptions that follow: If an argument to a
function has an invalid value (such as a value outside the domain of
the function, or a pointer outside the address space of the program, or
a null pointer, or a pointer to non-modifiable storage when the
corresponding parameter is not const-qualified) or a type (after
promotion) not expected by a function with variable number of
arguments, the behavior is undefined."

To avoid this, add an early return when nf_link_info is NULL to prevent
calling qsort with a NULL pointer.

Signed-off-by: Kuan-Wei Chiu <visitorckw@...il.com>
Signed-off-by: Andrii Nakryiko <andrii@...nel.org>
Reviewed-by: Quentin Monnet <qmo@...nel.org>
Link: https://lore.kernel.org/bpf/20240910150207.3179306-1-visitorckw@gmail.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 tools/bpf/bpftool/net.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tools/bpf/bpftool/net.c b/tools/bpf/bpftool/net.c
index 66a8ce8ae0127..bd4e66d514f14 100644
--- a/tools/bpf/bpftool/net.c
+++ b/tools/bpf/bpftool/net.c
@@ -819,6 +819,9 @@ static void show_link_netfilter(void)
 		nf_link_count++;
 	}
 
+	if (!nf_link_info)
+		return;
+
 	qsort(nf_link_info, nf_link_count, sizeof(*nf_link_info), netfilter_link_compar);
 
 	for (id = 0; id < nf_link_count; id++) {
-- 
2.43.0