bpf: Fix UAF in task local storage

When task local storage was generalized for tracing programs, the
bpf_task_local_storage callback was moved from a BPF LSM hook
callback for security_task_free LSM hook to it's own callback. But a
failure case in bad_fork_cleanup_security was missed which, when
triggered, led to a dangling task owner pointer and a subsequent
use-after-free. Move the bpf_task_storage_free to the very end of
free_task to handle all failure cases.

This issue was noticed when a BPF LSM program was attached to the
task_alloc hook on a kernel with KASAN enabled. The program used
bpf_task_storage_get to copy the task local storage from the current
task to the new task being created.

Fixes: a10787e6d58c ("bpf: Enable task local storage for tracing programs")
Reported-by: Kuba Piecuch <jpiecuch@google.com>
Signed-off-by: KP Singh <kpsingh@kernel.org>
Acked-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20230602002612.1117381-1-kpsingh@kernel.org
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

diff --git a/kernel/fork.c b/kernel/fork.c
index ed4e01d..cb20f9f 100644 (file)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -627,6 +627,7 @@ void free_task(struct task_struct *tsk)
        arch_release_task_struct(tsk);
        if (tsk->flags & PF_KTHREAD)
                free_kthread_struct(tsk);
+       bpf_task_storage_free(tsk);
        free_task_struct(tsk);
 }
 EXPORT_SYMBOL(free_task);
@@ -979,7 +980,6 @@ void __put_task_struct(struct task_struct *tsk)
        cgroup_free(tsk);
        task_numa_free(tsk, true);
        security_task_free(tsk);
-       bpf_task_storage_free(tsk);
        exit_creds(tsk);
        delayacct_tsk_free(tsk);
        put_signal_struct(tsk->signal);