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signal: avoid unconditional siginfo copy in send_signal_locked()

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send_signal_locked() unconditionally copies siginfo before the namespace
translation to avoid corrupting a shared siginfo.

Not that I think this can actually hurt performance-wise, just it doesn't
look clean to me; the copy is only needed in the unlikely case when the
translation will actually change something.

Defer it to the two cases where si_pid/si_uid are rewritten, and while at
it add #ifdef's just for completeness.

Link: https://lore.kernel.org/akkaAgNfUby5_3nM@redhat.com
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Bradley Morgan <include@grrlz.net>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Eric Biederman <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Oleg Nesterov 2026-07-04 16:34:42 +02:00 committed by Andrew Morton
parent 306d71b091
commit 571999ccd1
1 changed files with 15 additions and 8 deletions
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23
kernel/signal.c
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@ -1181,7 +1181,7 @@ static inline bool has_si_pid_and_uid(struct kernel_siginfo *info)
int send_signal_locked(int sig, struct kernel_siginfo *info,
struct task_struct *t, enum pid_type type)
{
struct kernel_siginfo rewritten;
struct kernel_siginfo __maybe_unused rewritten;
/* Should SIGKILL or SIGSTOP be received by a pid namespace init? */
bool force = false;
@ -1193,27 +1193,34 @@ int send_signal_locked(int sig, struct kernel_siginfo *info,
force = true;
} else if (has_si_pid_and_uid(info)) {
/* SIGKILL and SIGSTOP is special or has ids */
#ifdef CONFIG_USER_NS
struct user_namespace *t_user_ns;
rewritten = *info;
info = &rewritten;
kuid_t uid;
rcu_read_lock();
t_user_ns = task_cred_xxx(t, user_ns);
if (current_user_ns() != t_user_ns) {
kuid_t uid = make_kuid(current_user_ns(), info->si_uid);
info->si_uid = from_kuid_munged(t_user_ns, uid);
rewritten = *info;
info = &rewritten;
uid = make_kuid(current_user_ns(), info->si_uid);
rewritten.si_uid = from_kuid_munged(t_user_ns, uid);
}
rcu_read_unlock();
#endif
/* A kernel generated signal? */
force = (info->si_code == SI_KERNEL);
#ifdef CONFIG_PID_NS
/* From an ancestor pid namespace? */
if (!task_pid_nr_ns(current, task_active_pid_ns(t))) {
info->si_pid = 0;
if (info != &rewritten) {
rewritten = *info;
info = &rewritten;
}
rewritten.si_pid = 0;
force = true;
}
#endif
}
return __send_signal_locked(sig, info, t, type, force);
}