seccomp, filter: add and use bpf_prog_create_from_user from seccomp

Seccomp has always been a special candidate when it comes to preparation
of its filters in seccomp_prepare_filter(). Due to the extra checks and
filter rewrite it partially duplicates code and has BPF internals exposed.

This patch adds a generic API inside the BPF code code that seccomp can use
and thus keep it's filter preparation code minimal and better maintainable.
The other side-effect is that now classic JITs can add seccomp support as
well by only providing a BPF_LDX | BPF_W | BPF_ABS translation.

Tested with seccomp and BPF test suites.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Nicolas Schichan <nschichan@freebox.fr>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Kees Cook <keescook@chromium.org>
Acked-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 49 insertions, 2 deletions

diff --git a/net/core/filter.c b/net/core/filter.c
index 45c015d6b974..a831f193e2c7 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -991,8 +991,8 @@ out_err:
 	return ERR_PTR(err);
 }
 
-struct bpf_prog *bpf_prepare_filter(struct bpf_prog *fp,
-				    bpf_aux_classic_check_t trans)
+static struct bpf_prog *bpf_prepare_filter(struct bpf_prog *fp,
+					   bpf_aux_classic_check_t trans)
 {
 	int err;
 
@@ -1074,6 +1074,53 @@ int bpf_prog_create(struct bpf_prog **pfp, struct sock_fprog_kern *fprog)
 }
 EXPORT_SYMBOL_GPL(bpf_prog_create);
 
+/**
+ *	bpf_prog_create_from_user - create an unattached filter from user buffer
+ *	@pfp: the unattached filter that is created
+ *	@fprog: the filter program
+ *	@trans: post-classic verifier transformation handler
+ *
+ * This function effectively does the same as bpf_prog_create(), only
+ * that it builds up its insns buffer from user space provided buffer.
+ * It also allows for passing a bpf_aux_classic_check_t handler.
+ */
+int bpf_prog_create_from_user(struct bpf_prog **pfp, struct sock_fprog *fprog,
+			      bpf_aux_classic_check_t trans)
+{
+	unsigned int fsize = bpf_classic_proglen(fprog);
+	struct bpf_prog *fp;
+
+	/* Make sure new filter is there and in the right amounts. */
+	if (fprog->filter == NULL)
+		return -EINVAL;
+
+	fp = bpf_prog_alloc(bpf_prog_size(fprog->len), 0);
+	if (!fp)
+		return -ENOMEM;
+
+	if (copy_from_user(fp->insns, fprog->filter, fsize)) {
+		__bpf_prog_free(fp);
+		return -EFAULT;
+	}
+
+	fp->len = fprog->len;
+	/* Since unattached filters are not copied back to user
+	 * space through sk_get_filter(), we do not need to hold
+	 * a copy here, and can spare us the work.
+	 */
+	fp->orig_prog = NULL;
+
+	/* bpf_prepare_filter() already takes care of freeing
+	 * memory in case something goes wrong.
+	 */
+	fp = bpf_prepare_filter(fp, trans);
+	if (IS_ERR(fp))
+		return PTR_ERR(fp);
+
+	*pfp = fp;
+	return 0;
+}
+
 void bpf_prog_destroy(struct bpf_prog *fp)
 {
 	__bpf_prog_release(fp);