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bpf: reject stores into ctx via st and xadd

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[ 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: d691f9e8d4 ("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>
This commit is contained in:
Daniel Borkmann 2018-01-30 03:37:46 +01:00 committed by Greg Kroah-Hartman
parent 02662601a2
commit faa74a862a
1 changed files with 19 additions and 0 deletions
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19
kernel/bpf/verifier.c
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@ -683,6 +683,13 @@ static bool is_pointer_value(struct verifier_env *env, int regno)
}
}
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_env *env, struct bpf_insn *insn)
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 *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,