When tot_len is not provided by the user, bpf_skb_fib_lookup() resolves the FIB result's output device via dev_get_by_index_rcu() to check skb forwardability and fill in mtu_result. The returned pointer is dereferenced without a NULL check. If the device is concurrently unregistered, dev_get_by_index_rcu() returns NULL and is_skb_forwardable() crashes at dev->flags: KASAN: null-ptr-deref in range [0x00000000000000b0-0x00000000000000b7] Call Trace: is_skb_forwardable (include/linux/netdevice.h:4365) bpf_skb_fib_lookup (net/core/filter.c:6446) bpf_prog_test_run_skb (net/bpf/test_run.c) __sys_bpf (kernel/bpf/syscall.c) Add the missing NULL check, returning -ENODEV to be consistent with how bpf_ipv4_fib_lookup() and bpf_ipv6_fib_lookup() handle the same condition. Fixes: 4f74fede40df ("bpf: Add mtu checking to FIB forwarding helper") Reported-by: Xiang Mei Signed-off-by: Weiming Shi Acked-by: Paul Chaignon --- v2: Fix Fixes tag: 4f74fede40df, not e1850ea9bd9e (Jiayuan Chen) Add unlikely() to match bpf_ipv{4,6}_fib_lookup() style (Paul Chaignon) net/core/filter.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/net/core/filter.c b/net/core/filter.c index 78b548158fb0..5b4aa9faa707 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -6450,6 +6450,8 @@ BPF_CALL_4(bpf_skb_fib_lookup, struct sk_buff *, skb, * against MTU of FIB lookup resulting net_device */ dev = dev_get_by_index_rcu(net, params->ifindex); + if (unlikely(!dev)) + return -ENODEV; if (!is_skb_forwardable(dev, skb)) rc = BPF_FIB_LKUP_RET_FRAG_NEEDED; -- 2.43.0