[PATCH bpf-next] bpf: prevent leak of lsm program after failed attach

[PATCH bpf-next] bpf: prevent leak of lsm program after failed attach

[Milan Landaverde]

In [0], we added the ability to bpf_prog_attach LSM programs to cgroups,
but in our validation to make sure the prog is meant to be attached to
BPF_LSM_CGROUP, we return too early if the check fails. This results in
lack of decrementing prog's refcnt (through bpf_prog_put)
leaving the LSM program alive past the point of the expected lifecycle.
This fix allows for the decrement to take place.

[0] https://lore.kernel.org/all/20220628174314.1216643-4-sdf@google.com/

Fixes: 69fd337a975c ("bpf: per-cgroup lsm flavor")
Signed-off-by: Milan Landaverde <milan@mdaverde.com>
---
 kernel/bpf/syscall.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 35972afb6850..64131f88c553 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3518,9 +3518,9 @@ static int bpf_prog_attach(const union bpf_attr *attr)
 	case BPF_PROG_TYPE_LSM:
 		if (ptype == BPF_PROG_TYPE_LSM &&
 		    prog->expected_attach_type != BPF_LSM_CGROUP)
-			return -EINVAL;
-
-		ret = cgroup_bpf_prog_attach(attr, ptype, prog);
+			ret = -EINVAL;
+		else
+			ret = cgroup_bpf_prog_attach(attr, ptype, prog);
 		break;
 	default:
 		ret = -EINVAL;
-- 
2.34.1

Re: [PATCH bpf-next] bpf: prevent leak of lsm program after failed attach

[Stanislav Fomichev]

On Tue, Dec 13, 2022 at 9:58 AM Milan Landaverde <milan@mdaverde.com> wrote:
>
> In [0], we added the ability to bpf_prog_attach LSM programs to cgroups,
> but in our validation to make sure the prog is meant to be attached to
> BPF_LSM_CGROUP, we return too early if the check fails. This results in
> lack of decrementing prog's refcnt (through bpf_prog_put)
> leaving the LSM program alive past the point of the expected lifecycle.
> This fix allows for the decrement to take place.
>
> [0] https://lore.kernel.org/all/20220628174314.1216643-4-sdf@google.com/
>
> Fixes: 69fd337a975c ("bpf: per-cgroup lsm flavor")
> Signed-off-by: Milan Landaverde <milan@mdaverde.com>

Makes sense, thank you!

Reviewed-by: Stanislav Fomichev <sdf@google.com>

> ---
>  kernel/bpf/syscall.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 35972afb6850..64131f88c553 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -3518,9 +3518,9 @@ static int bpf_prog_attach(const union bpf_attr *attr)
>         case BPF_PROG_TYPE_LSM:
>                 if (ptype == BPF_PROG_TYPE_LSM &&
>                     prog->expected_attach_type != BPF_LSM_CGROUP)
> -                       return -EINVAL;
> -
> -               ret = cgroup_bpf_prog_attach(attr, ptype, prog);
> +                       ret = -EINVAL;
> +               else
> +                       ret = cgroup_bpf_prog_attach(attr, ptype, prog);
>                 break;
>         default:
>                 ret = -EINVAL;
> --
> 2.34.1
>

Re: [PATCH bpf-next] bpf: prevent leak of lsm program after failed attach

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Martin KaFai Lau <martin.lau@kernel.org>:

On Tue, 13 Dec 2022 12:57:14 -0500 you wrote:
> In [0], we added the ability to bpf_prog_attach LSM programs to cgroups,
> but in our validation to make sure the prog is meant to be attached to
> BPF_LSM_CGROUP, we return too early if the check fails. This results in
> lack of decrementing prog's refcnt (through bpf_prog_put)
> leaving the LSM program alive past the point of the expected lifecycle.
> This fix allows for the decrement to take place.
> 
> [...]

Here is the summary with links:
  - [bpf-next] bpf: prevent leak of lsm program after failed attach
    https://git.kernel.org/bpf/bpf-next/c/2958c237fd1e

You are awesome, thank you!
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