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bpf: Remove nmi_uaccess_okay() check in bpf_send_signal_common()

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nmi_uaccess_okay() takes no task argument and is a statement about
current. When commit 6280cf718d ("bpf: Implement bpf_send_signal_task()
kfunc") made the PF_KTHREAD/PF_EXITING and is_global_init() test the
supplied task, nmi_uaccess_okay() was left testing current.

As a result bpf_send_signal_task() returns -EPERM whenever the
calling context happens to be a kernel thread, regardless of which task
the signal is aimed at. The same call with the same target succeeds or
fails depending only on what the CPU was running:

  bpf_send_signal_task() from tp_btf/workqueue_execute_start : -EPERM
  bpf_send_signal_task() from tp_btf/sys_enter               : 0

The check was carried over from bpf_probe_write_user() when
bpf_send_signal() was added in commit 8b401f9ed2 ("bpf: implement
bpf_send_signal() helper"). There it guards a user memory write, but
bpf_send_signal_common() does no user memory access, so the check has
nothing to guard here. It is also already a no-op outside x86.

Remove it, and drop the part of the comment above it that described
the memory access checks, as none remain.

Fixes: 6280cf718d ("bpf: Implement bpf_send_signal_task() kfunc")
Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Aditya Sharma <adi.sharma@zohomail.in>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20260819124324.43162-1-adi.sharma@zohomail.in/T/#u
Link: https://patch.msgid.link/20261001072449.1377267-2-adi.sharma@zohomail.in
This commit is contained in:
Aditya Sharma 2026-10-01 12:54:48 +05:30 committed by Alexei Starovoitov
parent b93cf2c8a0
commit 93bd472336
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1 changed files with 3 additions and 6 deletions
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9
kernel/trace/bpf_trace.c
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@ -867,15 +867,12 @@ static int bpf_send_signal_common(u32 sig, enum pid_type type, struct task_struc
siginfo = &info;
}
/* Similar to bpf_probe_write_user, task needs to be
* in a sound condition and kernel memory access be
* permitted in order to send signal to the current
* task.
/*
* Similar to bpf_probe_write_user, task needs to be
* in a sound condition.
*/
if (unlikely(task->flags & (PF_KTHREAD | PF_EXITING)))
return -EPERM;
if (unlikely(!nmi_uaccess_okay()))
return -EPERM;
/* Task should not be pid=1 to avoid kernel panic. */
if (unlikely(is_global_init(task)))
return -EPERM;