bpf: reject wrong sized filters earlier

BugLink: https://bugs.launchpad.net/bugs/1830176

commit f7bd9e36 upstream.

Add a bpf_check_basics_ok() and reject filters that are of invalid
size much earlier, so we don't do any useless work such as invoking
bpf_prog_alloc(). Currently, rejection happens in bpf_check_classic()
only, but it's really unnecessarily late and they should be rejected
at earliest point. While at it, also clean up one bpf_prog_size() to
make it consistent with the remaining invocations.
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Zubin Mithra <zsm@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

net/core/filter.c

@@ -742,6 +742,17 @@ static bool chk_code_allowed(u16 code_to_probe)
 	return codes[code_to_probe];
 }
 
+static bool bpf_check_basics_ok(const struct sock_filter *filter,
+				unsigned int flen)
+{
+	if (filter == NULL)
+		return false;
+	if (flen == 0 || flen > BPF_MAXINSNS)
+		return false;
+
+	return true;
+}
+
 /**
  *	bpf_check_classic - verify socket filter code
  *	@filter: filter to verify
@@ -762,9 +773,6 @@ static int bpf_check_classic(const struct sock_filter *filter,
 	bool anc_found;
 	int pc;
 
-	if (flen == 0 || flen > BPF_MAXINSNS)
-		return -EINVAL;
-
 	/* Check the filter code now */
 	for (pc = 0; pc < flen; pc++) {
 		const struct sock_filter *ftest = &filter[pc];
@@ -1061,7 +1069,7 @@ int bpf_prog_create(struct bpf_prog **pfp, struct sock_fprog_kern *fprog)
 	struct bpf_prog *fp;
 
 	/* Make sure new filter is there and in the right amounts. */
-	if (fprog->filter == NULL)
+	if (!bpf_check_basics_ok(fprog->filter, fprog->len))
 		return -EINVAL;
 
 	fp = bpf_prog_alloc(bpf_prog_size(fprog->len), 0);
@@ -1108,7 +1116,7 @@ int bpf_prog_create_from_user(struct bpf_prog **pfp, struct sock_fprog *fprog,
 	int err;
 
 	/* Make sure new filter is there and in the right amounts. */
-	if (fprog->filter == NULL)
+	if (!bpf_check_basics_ok(fprog->filter, fprog->len))
 		return -EINVAL;
 
 	fp = bpf_prog_alloc(bpf_prog_size(fprog->len), 0);
@@ -1188,7 +1196,6 @@ int __sk_attach_filter(struct sock_fprog *fprog, struct sock *sk,
 		       bool locked)
 {
 	unsigned int fsize = bpf_classic_proglen(fprog);
-	unsigned int bpf_fsize = bpf_prog_size(fprog->len);
 	struct bpf_prog *prog;
 	int err;
 
@@ -1196,10 +1203,10 @@ int __sk_attach_filter(struct sock_fprog *fprog, struct sock *sk,
 		return -EPERM;
 
 	/* Make sure new filter is there and in the right amounts. */
-	if (fprog->filter == NULL)
+	if (!bpf_check_basics_ok(fprog->filter, fprog->len))
 		return -EINVAL;
 
-	prog = bpf_prog_alloc(bpf_fsize, 0);
+	prog = bpf_prog_alloc(bpf_prog_size(fprog->len), 0);
 	if (!prog)
 		return -ENOMEM;