[PATCH AUTOSEL 6.6 139/139] bpftool: Fix undefined behavior in qsort(NULL, 0, ...)

Sasha Levin
2024-09-25T12:18:08Z

From: Kuan-Wei Chiu <visitorckw@gmail.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@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Quentin Monnet <qmo@kernel.org>
Link: https://lore.kernel.org/bpf/20240910150207.3179306-1-visitorckw@gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.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 fd54ff436493f..28e9417a5c2e3 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