2022-12-13 18:15:00

by Milan Landaverde

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

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/[email protected]/

Fixes: 69fd337a975c ("bpf: per-cgroup lsm flavor")
Signed-off-by: Milan Landaverde <[email protected]>
---
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

2022-12-13 19:49:54

by Stanislav Fomichev

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

On Tue, Dec 13, 2022 at 9:58 AM Milan Landaverde <[email protected]> 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/[email protected]/
>
> Fixes: 69fd337a975c ("bpf: per-cgroup lsm flavor")
> Signed-off-by: Milan Landaverde <[email protected]>

Makes sense, thank you!

Reviewed-by: Stanislav Fomichev <[email protected]>

> ---
> 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
>

2022-12-14 02:31:23

by patchwork-bot+netdevbpf

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

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Martin KaFai Lau <[email protected]>:

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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