General assumption is that single program can hold up to BPF_MAXINSNS, that is, 4096 number of instructions. It is the case with cBPF and that limit was carried over to eBPF. When recently testing digest, I noticed that it's actually not possible to feed 4096 instructions via bpf(2).
The check for > BPF_MAXINSNS was added back then to bpf_check() in cbd357008604 ("bpf: verifier (add ability to receive verification log)"). However, 09756af46893 ("bpf: expand BPF syscall with program load/unload") added yet another check that comes before that into bpf_prog_load(), but this time bails out already in case of >= BPF_MAXINSNS. Fix it up and perform the check early in bpf_prog_load(), so we can drop the second one in bpf_check(). It makes sense, because also a 0 insn program is useless and we don't want to waste any resources doing work up to bpf_check() point. The existing bpf(2) man page documents E2BIG as the official error for such cases, so just stick with it as well. Fixes: 09756af46893 ("bpf: expand BPF syscall with program load/unload") Signed-off-by: Daniel Borkmann <dan...@iogearbox.net> Acked-by: Alexei Starovoitov <a...@kernel.org> --- ( net-next is just fine imho. ) kernel/bpf/syscall.c | 4 ++-- kernel/bpf/verifier.c | 3 --- 2 files changed, 2 insertions(+), 5 deletions(-) diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index c0d2b42..88f609f 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -786,8 +786,8 @@ static int bpf_prog_load(union bpf_attr *attr) /* eBPF programs must be GPL compatible to use GPL-ed functions */ is_gpl = license_is_gpl_compatible(license); - if (attr->insn_cnt >= BPF_MAXINSNS) - return -EINVAL; + if (attr->insn_cnt == 0 || attr->insn_cnt > BPF_MAXINSNS) + return -E2BIG; if (type == BPF_PROG_TYPE_KPROBE && attr->kern_version != LINUX_VERSION_CODE) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index cb37339..da9fb2a 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -3133,9 +3133,6 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr) struct bpf_verifier_env *env; int ret = -EINVAL; - if ((*prog)->len <= 0 || (*prog)->len > BPF_MAXINSNS) - return -E2BIG; - /* 'struct bpf_verifier_env' can be global, but since it's not small, * allocate/free it every time bpf_check() is called */ -- 1.9.3