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authorDaniel Borkmann <daniel@iogearbox.net>2018-01-29 00:36:46 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2018-01-31 14:03:50 +0100
commita17536742bb9a5df561cce54c7cc3cd1e2cd480d (patch)
treec1d26cf0234b4613a2e396d2c7a40a9331a96e83 /kernel
parentca0a0967205b65a197dccb80688f3588cc14d745 (diff)
bpf: reject stores into ctx via st and xadd
[ 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>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/bpf/verifier.c19
1 files changed, 19 insertions, 0 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index ab2be68e376a..f9339c3219bc 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -986,6 +986,13 @@ static bool is_pointer_value(struct bpf_verifier_env *env, int regno)
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_verifier_env *env, int insn_idx, struct bpf_ins
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_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_idx, insn->dst_reg, insn->off,
BPF_SIZE(insn->code), BPF_WRITE,