Patch "bpf: reject stores into ctx via st and xadd" has been added to the 4.14-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    bpf: reject stores into ctx via st and xadd

to the 4.14-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     bpf-reject-stores-into-ctx-via-st-and-xadd.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Mon Jan 29 13:14:09 CET 2018
From: Daniel Borkmann <daniel@iogearbox.net>
Date: Mon, 29 Jan 2018 00:36:46 +0100
Subject: bpf: reject stores into ctx via st and xadd
To: gregkh@linuxfoundation.org
Cc: ast@kernel.org, stable@vger.kernel.org, Daniel Borkmann <daniel@iogearbox.net>
Message-ID: <20180128233647.21154-6-daniel@iogearbox.net>

From: Daniel Borkmann <daniel@iogearbox.net>

[ upstream commit f37a8cb84cce18762e8f86a70bd6a49a66ab964c ]

Alexei found that verifier does not reject stores into context
via BPF_ST instead of BPF_STX. And while looking at it, we
also should not allow XADD variant of BPF_STX.

The context rewriter is only assuming either BPF_LDX_MEM- or
BPF_STX_MEM-type operations, thus reject anything other than
that so that assumptions in the rewriter properly hold. Add
test cases as well for BPF selftests.

Fixes: d691f9e8d440 ("bpf: allow programs to write to certain skb fields")
Reported-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 kernel/bpf/verifier.c                       |   19 ++++++++++++++++++
 tools/testing/selftests/bpf/test_verifier.c |   29 ++++++++++++++++++++++++++--
 2 files changed, 46 insertions(+), 2 deletions(-)

--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -986,6 +986,13 @@ static bool is_pointer_value(struct bpf_
 	return __is_pointer_value(env->allow_ptr_leaks, &env->cur_state.regs[regno]);
 }
 
+static bool is_ctx_reg(struct bpf_verifier_env *env, int regno)
+{
+	const struct bpf_reg_state *reg = &env->cur_state.regs[regno];
+
+	return reg->type == PTR_TO_CTX;
+}
+
 static int check_pkt_ptr_alignment(const struct bpf_reg_state *reg,
 				   int off, int size, bool strict)
 {
@@ -1258,6 +1265,12 @@ static int check_xadd(struct bpf_verifie
 		return -EACCES;
 	}
 
+	if (is_ctx_reg(env, insn->dst_reg)) {
+		verbose("BPF_XADD stores into R%d context is not allowed\n",
+			insn->dst_reg);
+		return -EACCES;
+	}
+
 	/* check whether atomic_add can read the memory */
 	err = check_mem_access(env, insn_idx, insn->dst_reg, insn->off,
 			       BPF_SIZE(insn->code), BPF_READ, -1);
@@ -3859,6 +3872,12 @@ static int do_check(struct bpf_verifier_
 			if (err)
 				return err;
 
+			if (is_ctx_reg(env, insn->dst_reg)) {
+				verbose("BPF_ST stores into R%d context is not allowed\n",
+					insn->dst_reg);
+				return -EACCES;
+			}
+
 			/* check that memory (dst_reg + off) is writeable */
 			err = check_mem_access(env, insn_idx, insn->dst_reg, insn->off,
 					       BPF_SIZE(insn->code), BPF_WRITE,
--- a/tools/testing/selftests/bpf/test_verifier.c
+++ b/tools/testing/selftests/bpf/test_verifier.c
@@ -2596,6 +2596,29 @@ static struct bpf_test tests[] = {
 		.prog_type = BPF_PROG_TYPE_SCHED_CLS,
 	},
 	{
+		"context stores via ST",
+		.insns = {
+			BPF_MOV64_IMM(BPF_REG_0, 0),
+			BPF_ST_MEM(BPF_DW, BPF_REG_1, offsetof(struct __sk_buff, mark), 0),
+			BPF_EXIT_INSN(),
+		},
+		.errstr = "BPF_ST stores into R1 context is not allowed",
+		.result = REJECT,
+		.prog_type = BPF_PROG_TYPE_SCHED_CLS,
+	},
+	{
+		"context stores via XADD",
+		.insns = {
+			BPF_MOV64_IMM(BPF_REG_0, 0),
+			BPF_RAW_INSN(BPF_STX | BPF_XADD | BPF_W, BPF_REG_1,
+				     BPF_REG_0, offsetof(struct __sk_buff, mark), 0),
+			BPF_EXIT_INSN(),
+		},
+		.errstr = "BPF_XADD stores into R1 context is not allowed",
+		.result = REJECT,
+		.prog_type = BPF_PROG_TYPE_SCHED_CLS,
+	},
+	{
 		"direct packet access: test1",
 		.insns = {
 			BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1,
@@ -4317,7 +4340,8 @@ static struct bpf_test tests[] = {
 		.fixup_map1 = { 2 },
 		.errstr_unpriv = "R2 leaks addr into mem",
 		.result_unpriv = REJECT,
-		.result = ACCEPT,
+		.result = REJECT,
+		.errstr = "BPF_XADD stores into R1 context is not allowed",
 	},
 	{
 		"leak pointer into ctx 2",
@@ -4331,7 +4355,8 @@ static struct bpf_test tests[] = {
 		},
 		.errstr_unpriv = "R10 leaks addr into mem",
 		.result_unpriv = REJECT,
-		.result = ACCEPT,
+		.result = REJECT,
+		.errstr = "BPF_XADD stores into R1 context is not allowed",
 	},
 	{
 		"leak pointer into ctx 3",


Patches currently in stable-queue which might be from daniel@iogearbox.net are

queue-4.14/bpf-avoid-false-sharing-of-map-refcount-with-max_entries.patch
queue-4.14/bpf-reject-stores-into-ctx-via-st-and-xadd.patch
queue-4.14/bpf-fix-32-bit-divide-by-zero.patch
queue-4.14/bpf-fix-divides-by-zero.patch
queue-4.14/bpf-arm64-fix-stack_depth-tracking-in-combination-with-tail-calls.patch
queue-4.14/bpf-introduce-bpf_jit_always_on-config.patch