Code: void bpf_int_jit_compile(struct bpf_prog *prog)
{
	struct bpf_binary_header *header = NULL;
	int proglen, oldproglen = 0;
	struct jit_context ctx = {};
	u8 *image = NULL;
	int *addrs;
	int pass;
	int i;

	if (!bpf_jit_enable)
		return;

	if (!prog || !prog->len)
		return;

	addrs = kmalloc(prog->len * sizeof(*addrs), GFP_KERNEL);
	if (!addrs)
		return;

	/* Before first pass, make a rough estimation of addrs[]
	 * each bpf instruction is translated to less than 64 bytes
	 */
	for (proglen = 0, i = 0; i < prog->len; i++) {
		proglen += 64;
		addrs[i] = proglen;
 	}
 	ctx.cleanup_addr = proglen;
 
	for (pass = 0; pass < 10; pass++) {
 		proglen = do_jit(prog, addrs, image, oldproglen, &ctx);
 		if (proglen <= 0) {
 			image = NULL;
			if (header)
				bpf_jit_binary_free(header);
			goto out;
		}
		if (image) {
			if (proglen != oldproglen) {
				pr_err("bpf_jit: proglen=%d != oldproglen=%d\n",
				       proglen, oldproglen);
				goto out;
			}
			break;
		}
		if (proglen == oldproglen) {
			header = bpf_jit_binary_alloc(proglen, &image,
						      1, jit_fill_hole);
			if (!header)
				goto out;
		}
		oldproglen = proglen;
	}

	if (bpf_jit_enable > 1)
		bpf_jit_dump(prog->len, proglen, 0, image);

	if (image) {
		bpf_flush_icache(header, image + proglen);
		set_memory_ro((unsigned long)header, header->pages);
		prog->bpf_func = (void *)image;
		prog->jited = true;
	}
out:
	kfree(addrs);
}

Vulnerability Type: DoS 
CWE ID: CWE-17
Summary: The bpf_int_jit_compile function in arch/x86/net/bpf_jit_comp.c in the Linux kernel before 4.0.6 allows local users to cause a denial of service (system crash) by creating a packet filter and then loading crafted BPF instructions that trigger late convergence by the JIT compiler.
Commit Message: x86: bpf_jit: fix compilation of large bpf programs

x86 has variable length encoding. x86 JIT compiler is trying
to pick the shortest encoding for given bpf instruction.
While doing so the jump targets are changing, so JIT is doing
multiple passes over the program. Typical program needs 3 passes.
Some very short programs converge with 2 passes. Large programs
may need 4 or 5. But specially crafted bpf programs may hit the
pass limit and if the program converges on the last iteration
the JIT compiler will be producing an image full of 'int 3' insns.
Fix this corner case by doing final iteration over bpf program.

Fixes: 0a14842f5a3c ("net: filter: Just In Time compiler for x86-64")
Reported-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Tested-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>