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@xxxxxxxxx>
---
Changes in v2:
- Change from checking nf_link_count to checking nf_link_info.
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 968714b4c3d4..0ad684e810f3 100644
--- a/tools/bpf/bpftool/net.c
+++ b/tools/bpf/bpftool/net.c
@@ -824,6 +824,9 @@ 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++) {
--
2.34.1
