Introduce bpf_cgroup_read_xattr #5503
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All allocations of struct kernfs_iattrs are serialized through a global mutex. Simply do a racy allocation and let the first one win. I bet most callers are under inode->i_rwsem anyway and it wouldn't be needed but let's not require that. Signed-off-by: Christian Brauner <[email protected]> Acked-by: Greg Kroah-Hartman <[email protected]> Acked-by: Tejun Heo <[email protected]> Signed-off-by: Song Liu <[email protected]>
BPF programs, such as LSM and sched_ext, would benefit from tags on cgroups. One common practice to apply such tags is to set xattrs on cgroupfs folders. Introduce kfunc bpf_cgroup_read_xattr, which allows reading cgroup's xattr. Note that, we already have bpf_get_[file|dentry]_xattr. However, these two APIs are not ideal for reading cgroupfs xattrs, because: 1) These two APIs only works in sleepable contexts; 2) There is no kfunc that matches current cgroup to cgroupfs dentry. bpf_cgroup_read_xattr is generic and can be useful for many program types. It is also safe, because it requires trusted or rcu protected argument (KF_RCU). Therefore, we make it available to all program types. Signed-off-by: Song Liu <[email protected]> Acked-by: Tejun Heo <[email protected]>
Mark struct cgroup_subsys_state->cgroup as safe under RCU read lock. This will enable accessing css->cgroup from a bpf css iterator. Signed-off-by: Song Liu <[email protected]>
Add tests for different scenarios with bpf_cgroup_read_xattr: 1. Read cgroup xattr from bpf_cgroup_from_id; 2. Read cgroup xattr from bpf_cgroup_ancestor; 3. Read cgroup xattr from css_iter; 4. Use bpf_cgroup_read_xattr in LSM hook security_socket_connect. 5. Use bpf_cgroup_read_xattr in cgroup program. Signed-off-by: Song Liu <[email protected]>
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Pull request for series with
subject: Introduce bpf_cgroup_read_xattr
version: 3
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=974689