[CVE-2017-9150,X/Y/joule/aws/gke,1/1] bpf: don't let ldimm64 leak map addresses on unprivileged

From: Daniel Borkmann <daniel@iogearbox.net>

CVE-2017-9150

The patch fixes two things at once:

1) It checks the env->allow_ptr_leaks and only prints the map address to
   the log if we have the privileges to do so, otherwise it just dumps 0
   as we would when kptr_restrict is enabled on %pK. Given the latter is
   off by default and not every distro sets it, I don't want to rely on
   this, hence the 0 by default for unprivileged.

2) Printing of ldimm64 in the verifier log is currently broken in that
   we don't print the full immediate, but only the 32 bit part of the
   first insn part for ldimm64. Thus, fix this up as well; it's okay to
   access, since we verified all ldimm64 earlier already (including just
   constants) through replace_map_fd_with_map_ptr().

Fixes: 1be7f75d1668 ("bpf: enable non-root eBPF programs")
Fixes: cbd357008604 ("bpf: verifier (add ability to receive verification log)")
Reported-by: Jann Horn <jannh@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
(backported from commit 0d0e57697f162da4aa218b5feafe614fb666db07)
Signed-off-by: Wen-chien Jesse Sung <jesse.sung@canonical.com>
---
 kernel/bpf/verifier.c | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

On 21.06.2017 16:13, Wen-chien Jesse Sung wrote:
> From: Daniel Borkmann <daniel@iogearbox.net>
> 
> CVE-2017-9150
> 
> The patch fixes two things at once:
> 
> 1) It checks the env->allow_ptr_leaks and only prints the map address to
>    the log if we have the privileges to do so, otherwise it just dumps 0
>    as we would when kptr_restrict is enabled on %pK. Given the latter is
>    off by default and not every distro sets it, I don't want to rely on
>    this, hence the 0 by default for unprivileged.
> 
> 2) Printing of ldimm64 in the verifier log is currently broken in that
>    we don't print the full immediate, but only the 32 bit part of the
>    first insn part for ldimm64. Thus, fix this up as well; it's okay to
>    access, since we verified all ldimm64 earlier already (including just
>    constants) through replace_map_fd_with_map_ptr().
> 
> Fixes: 1be7f75d1668 ("bpf: enable non-root eBPF programs")
> Fixes: cbd357008604 ("bpf: verifier (add ability to receive verification log)")
> Reported-by: Jann Horn <jannh@google.com>
> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
> Acked-by: Alexei Starovoitov <ast@kernel.org>
> Signed-off-by: David S. Miller <davem@davemloft.net>
> (backported from commit 0d0e57697f162da4aa218b5feafe614fb666db07)
> Signed-off-by: Wen-chien Jesse Sung <jesse.sung@canonical.com>

Acked-by: Stefan Bader <stefan.bader@canonical.com>

> ---

The backport appear to look right. But this to be targeted only fo X/Y. Any of
the derivatives (or backports) will automatically get it when rebasing.

Thanks,
-Stefan

>  kernel/bpf/verifier.c | 21 ++++++++++++++++-----
>  1 file changed, 16 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 2cbfba7..85de509 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -313,7 +313,8 @@ static const char *const bpf_jmp_string[16] = {
>  	[BPF_EXIT >> 4] = "exit",
>  };
>  
> -static void print_bpf_insn(struct bpf_insn *insn)
> +static void print_bpf_insn(const struct verifier_env *env,
> +			   const struct bpf_insn *insn)
>  {
>  	u8 class = BPF_CLASS(insn->code);
>  
> @@ -377,9 +378,19 @@ static void print_bpf_insn(struct bpf_insn *insn)
>  				insn->code,
>  				bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
>  				insn->src_reg, insn->imm);
> -		} else if (BPF_MODE(insn->code) == BPF_IMM) {
> -			verbose("(%02x) r%d = 0x%x\n",
> -				insn->code, insn->dst_reg, insn->imm);
> +		} else if (BPF_MODE(insn->code) == BPF_IMM &&
> +			   BPF_SIZE(insn->code) == BPF_DW) {
> +			/* At this point, we already made sure that the second
> +			 * part of the ldimm64 insn is accessible.
> +			 */
> +			u64 imm = ((u64)(insn + 1)->imm << 32) | (u32)insn->imm;
> +			bool map_ptr = insn->src_reg == BPF_PSEUDO_MAP_FD;
> +
> +			if (map_ptr && !env->allow_ptr_leaks)
> +				imm = 0;
> +
> +			verbose("(%02x) r%d = 0x%llx\n", insn->code,
> +				insn->dst_reg, (unsigned long long)imm);
>  		} else {
>  			verbose("BUG_ld_%02x\n", insn->code);
>  			return;
> @@ -1758,7 +1769,7 @@ static int do_check(struct verifier_env *env)
>  
>  		if (log_level) {
>  			verbose("%d: ", insn_idx);
> -			print_bpf_insn(insn);
> +			print_bpf_insn(env, insn);
>  		}
>  
>  		if (class == BPF_ALU || class == BPF_ALU64) {
>