From e9eeec58c992c47b394e4f829e4f81b923b0a322 Mon Sep 17 00:00:00 2001 From: Yonghong Song Date: Wed, 4 Dec 2019 17:06:06 -0800 Subject: bpf: Fix a bug when getting subprog 0 jited image in check_attach_btf_id For jited bpf program, if the subprogram count is 1, i.e., there is no callees in the program, prog->aux->func will be NULL and prog->bpf_func points to image address of the program. If there is more than one subprogram, prog->aux->func is populated, and subprogram 0 can be accessed through either prog->bpf_func or prog->aux->func[0]. Other subprograms should be accessed through prog->aux->func[subprog_id]. This patch fixed a bug in check_attach_btf_id(), where prog->aux->func[subprog_id] is used to access any subprogram which caused a segfault like below: [79162.619208] BUG: kernel NULL pointer dereference, address: 0000000000000000 ...... [79162.634255] Call Trace: [79162.634974] ? _cond_resched+0x15/0x30 [79162.635686] ? kmem_cache_alloc_trace+0x162/0x220 [79162.636398] ? selinux_bpf_prog_alloc+0x1f/0x60 [79162.637111] bpf_prog_load+0x3de/0x690 [79162.637809] __do_sys_bpf+0x105/0x1740 [79162.638488] do_syscall_64+0x5b/0x180 [79162.639147] entry_SYSCALL_64_after_hwframe+0x44/0xa9 ...... Fixes: 5b92a28aae4d ("bpf: Support attaching tracing BPF program to other BPF programs") Reported-by: Eelco Chaudron Signed-off-by: Yonghong Song Signed-off-by: Alexei Starovoitov Link: https://lore.kernel.org/bpf/20191205010606.177774-1-yhs@fb.com --- kernel/bpf/verifier.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index a0482e1c4a77..034ef81f935b 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -9636,7 +9636,10 @@ static int check_attach_btf_id(struct bpf_verifier_env *env) ret = -EINVAL; goto out; } - addr = (long) tgt_prog->aux->func[subprog]->bpf_func; + if (subprog == 0) + addr = (long) tgt_prog->bpf_func; + else + addr = (long) tgt_prog->aux->func[subprog]->bpf_func; } else { addr = kallsyms_lookup_name(tname); if (!addr) { -- cgit