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 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++) {