Patch "bpf: reject stores into ctx via st and xadd" has been added to the 4.4-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 4.4-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-4.4 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 Thu Feb  1 09:05:44 CET 2018
From: Daniel Borkmann <daniel@iogearbox.net>
Date: Tue, 30 Jan 2018 03:37:46 +0100
Subject: bpf: reject stores into ctx via st and xadd
To: gregkh@linuxfoundation.org
Cc: ast@kernel.org, daniel@iogearbox.net, stable@vger.kernel.org
Message-ID: <7d49693fcf1d0f23f0f14e8da18acfe03da9fc18.1517279268.git.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 +++++++++++++++++++
 1 file changed, 19 insertions(+)

--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -683,6 +683,13 @@ static bool is_pointer_value(struct veri
 	}
 }
 
+static bool is_ctx_reg(struct verifier_env *env, int regno)
+{
+	const struct reg_state *reg = &env->cur_state.regs[regno];
+
+	return reg->type == PTR_TO_CTX;
+}
+
 /* check whether memory at (regno + off) is accessible for t = (read | write)
  * if t==write, value_regno is a register which value is stored into memory
  * if t==read, value_regno is a register which will receive the value from memory
@@ -779,6 +786,12 @@ static int check_xadd(struct verifier_en
 		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->dst_reg, insn->off,
 			       BPF_SIZE(insn->code), BPF_READ, -1);
@@ -1909,6 +1922,12 @@ static int do_check(struct verifier_env
 			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->dst_reg, insn->off,
 					       BPF_SIZE(insn->code), BPF_WRITE,


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

queue-4.4/bpf-fix-branch-pruning-logic.patch
queue-4.4/bpf-avoid-false-sharing-of-map-refcount-with-max_entries.patch
queue-4.4/x86-bpf_jit-small-optimization-in-emit_bpf_tail_call.patch
queue-4.4/bpf-reject-stores-into-ctx-via-st-and-xadd.patch
queue-4.4/bpf-fix-32-bit-divide-by-zero.patch
queue-4.4/bpf-fix-bpf_tail_call-x64-jit.patch
queue-4.4/bpf-arsh-is-not-supported-in-32-bit-alu-thus-reject-it.patch
queue-4.4/bpf-fix-divides-by-zero.patch
queue-4.4/bpf-introduce-bpf_jit_always_on-config.patch