Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf

Daniel Borkmann says:

====================
pull-request: bpf 2018-05-18

The following pull-request contains BPF updates for your *net* tree.

The main changes are:

1) Fix two bugs in sockmap, a use after free in sockmap's error path
   from sock_map_ctx_update_elem() where we mistakenly drop a reference
   we didn't take prior to that, and in the same function fix a race
   in bpf_prog_inc_not_zero() where we didn't use the progs from prior
   READ_ONCE(), from John.

2) Reject program expansions once we figure out that their jump target
   which crosses patchlet boundaries could otherwise get truncated in
   insn->off space, from Daniel.

3) Check the return value of fopen() in BPF selftest's test_verifier
   where we determine whether unpriv BPF is disabled, and iff we do
   fail there then just assume it is disabled. This fixes a segfault
   when used with older kernels, from Jesper.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

kernel/bpf/core.c

@@ -218,47 +218,84 @@ int bpf_prog_calc_tag(struct bpf_prog *fp)
 	return 0;
 }
 
-static void bpf_adj_branches(struct bpf_prog *prog, u32 pos, u32 delta)
+static int bpf_adj_delta_to_imm(struct bpf_insn *insn, u32 pos, u32 delta,
+				u32 curr, const bool probe_pass)
 {
+	const s64 imm_min = S32_MIN, imm_max = S32_MAX;
+	s64 imm = insn->imm;
+
+	if (curr < pos && curr + imm + 1 > pos)
+		imm += delta;
+	else if (curr > pos + delta && curr + imm + 1 <= pos + delta)
+		imm -= delta;
+	if (imm < imm_min || imm > imm_max)
+		return -ERANGE;
+	if (!probe_pass)
+		insn->imm = imm;
+	return 0;
+}
+
+static int bpf_adj_delta_to_off(struct bpf_insn *insn, u32 pos, u32 delta,
+				u32 curr, const bool probe_pass)
+{
+	const s32 off_min = S16_MIN, off_max = S16_MAX;
+	s32 off = insn->off;
+
+	if (curr < pos && curr + off + 1 > pos)
+		off += delta;
+	else if (curr > pos + delta && curr + off + 1 <= pos + delta)
+		off -= delta;
+	if (off < off_min || off > off_max)
+		return -ERANGE;
+	if (!probe_pass)
+		insn->off = off;
+	return 0;
+}
+
+static int bpf_adj_branches(struct bpf_prog *prog, u32 pos, u32 delta,
+			    const bool probe_pass)
+{
+	u32 i, insn_cnt = prog->len + (probe_pass ? delta : 0);
 	struct bpf_insn *insn = prog->insnsi;
-	u32 i, insn_cnt = prog->len;
-	bool pseudo_call;
-	u8 code;
-	int off;
+	int ret = 0;
 
 	for (i = 0; i < insn_cnt; i++, insn++) {
+		u8 code;
+
+		/* In the probing pass we still operate on the original,
+		 * unpatched image in order to check overflows before we
+		 * do any other adjustments. Therefore skip the patchlet.
+		 */
+		if (probe_pass && i == pos) {
+			i += delta + 1;
+			insn++;
+		}
 		code = insn->code;
-		if (BPF_CLASS(code) != BPF_JMP)
-			continue;
-		if (BPF_OP(code) == BPF_EXIT)
+		if (BPF_CLASS(code) != BPF_JMP ||
+		    BPF_OP(code) == BPF_EXIT)
 			continue;
+		/* Adjust offset of jmps if we cross patch boundaries. */
 		if (BPF_OP(code) == BPF_CALL) {
-			if (insn->src_reg == BPF_PSEUDO_CALL)
-				pseudo_call = true;
-			else
+			if (insn->src_reg != BPF_PSEUDO_CALL)
 				continue;
+			ret = bpf_adj_delta_to_imm(insn, pos, delta, i,
+						   probe_pass);
 		} else {
-			pseudo_call = false;
+			ret = bpf_adj_delta_to_off(insn, pos, delta, i,
+						   probe_pass);
 		}
-		off = pseudo_call ? insn->imm : insn->off;
-
-		/* Adjust offset of jmps if we cross boundaries. */
-		if (i < pos && i + off + 1 > pos)
-			off += delta;
-		else if (i > pos + delta && i + off + 1 <= pos + delta)
-			off -= delta;
-
-		if (pseudo_call)
-			insn->imm = off;
-		else
-			insn->off = off;
+		if (ret)
+			break;
 	}
+
+	return ret;
 }
 
 struct bpf_prog *bpf_patch_insn_single(struct bpf_prog *prog, u32 off,
 				       const struct bpf_insn *patch, u32 len)
 {
 	u32 insn_adj_cnt, insn_rest, insn_delta = len - 1;
+	const u32 cnt_max = S16_MAX;
 	struct bpf_prog *prog_adj;
 
 	/* Since our patchlet doesn't expand the image, we're done. */
@@ -269,6 +306,15 @@ struct bpf_prog *bpf_patch_insn_single(struct bpf_prog *prog, u32 off,
 
 	insn_adj_cnt = prog->len + insn_delta;
 
+	/* Reject anything that would potentially let the insn->off
+	 * target overflow when we have excessive program expansions.
+	 * We need to probe here before we do any reallocation where
+	 * we afterwards may not fail anymore.
+	 */
+	if (insn_adj_cnt > cnt_max &&
+	    bpf_adj_branches(prog, off, insn_delta, true))
+		return NULL;
+
 	/* Several new instructions need to be inserted. Make room
 	 * for them. Likely, there's no need for a new allocation as
 	 * last page could have large enough tailroom.
@@ -294,7 +340,11 @@ struct bpf_prog *bpf_patch_insn_single(struct bpf_prog *prog, u32 off,
 		sizeof(*patch) * insn_rest);
 	memcpy(prog_adj->insnsi + off, patch, sizeof(*patch) * len);
 
-	bpf_adj_branches(prog_adj, off, insn_delta);
+	/* We are guaranteed to not fail at this point, otherwise
+	 * the ship has sailed to reverse to the original state. An
+	 * overflow cannot happen at this point.
+	 */
+	BUG_ON(bpf_adj_branches(prog_adj, off, insn_delta, false));
 
 	return prog_adj;
 }

kernel/bpf/sockmap.c

@@ -1703,24 +1703,24 @@ static int sock_map_ctx_update_elem(struct bpf_sock_ops_kern *skops,
 		 * we increment the refcnt. If this is the case abort with an
 		 * error.
 		 */
-		verdict = bpf_prog_inc_not_zero(stab->bpf_verdict);
+		verdict = bpf_prog_inc_not_zero(verdict);
 		if (IS_ERR(verdict))
 			return PTR_ERR(verdict);
 
-		parse = bpf_prog_inc_not_zero(stab->bpf_parse);
+		parse = bpf_prog_inc_not_zero(parse);
 		if (IS_ERR(parse)) {
 			bpf_prog_put(verdict);
 			return PTR_ERR(parse);
 		}
 	}
 
 	if (tx_msg) {
-		tx_msg = bpf_prog_inc_not_zero(stab->bpf_tx_msg);
+		tx_msg = bpf_prog_inc_not_zero(tx_msg);
 		if (IS_ERR(tx_msg)) {
-			if (verdict)
-				bpf_prog_put(verdict);
-			if (parse)
+			if (parse && verdict) {
 				bpf_prog_put(parse);
+				bpf_prog_put(verdict);
+			}
 			return PTR_ERR(tx_msg);
 		}
 	}
@@ -1805,10 +1805,10 @@ static int sock_map_ctx_update_elem(struct bpf_sock_ops_kern *skops,
 out_free:
 	smap_release_sock(psock, sock);
 out_progs:
-	if (verdict)
-		bpf_prog_put(verdict);
-	if (parse)
+	if (parse && verdict) {
 		bpf_prog_put(parse);
+		bpf_prog_put(verdict);
+	}
 	if (tx_msg)
 		bpf_prog_put(tx_msg);
 	write_unlock_bh(&sock->sk_callback_lock);

net/core/filter.c

@@ -481,11 +481,18 @@ static int bpf_convert_filter(struct sock_filter *prog, int len,
 
 #define BPF_EMIT_JMP							\
 	do {								\
+		const s32 off_min = S16_MIN, off_max = S16_MAX;		\
+		s32 off;						\
+									\
 		if (target >= len || target < 0)			\
 			goto err;					\
-		insn->off = addrs ? addrs[target] - addrs[i] - 1 : 0;	\
+		off = addrs ? addrs[target] - addrs[i] - 1 : 0;		\
 		/* Adjust pc relative offset for 2nd or 3rd insn. */	\
-		insn->off -= insn - tmp_insns;				\
+		off -= insn - tmp_insns;				\
+		/* Reject anything not fitting into insn->off. */	\
+		if (off < off_min || off > off_max)			\
+			goto err;					\
+		insn->off = off;					\
 	} while (0)
 
 		case BPF_JMP | BPF_JA:

tools/testing/selftests/bpf/test_verifier.c

@@ -11713,6 +11713,11 @@ static void get_unpriv_disabled()
 	FILE *fd;
 
 	fd = fopen("/proc/sys/"UNPRIV_SYSCTL, "r");
+	if (!fd) {
+		perror("fopen /proc/sys/"UNPRIV_SYSCTL);
+		unpriv_disabled = true;
+		return;
+	}
 	if (fgets(buf, 2, fd) == buf && atoi(buf))
 		unpriv_disabled = true;
 	fclose(fd);