From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794404635; b=h+IKSQ+8LQcOedCWnPQz+9kdYnRkXpud2F7af/QQJv5l/zW9JpttVhWiwuVvveIRrSob jJEj4OxlaJttjVtta8BptQAGPx2ITbO9JC9ftEsiGzYNrNVx+I5rI60al9HkHTCWylkwq hs7veIdkDZ+sRvNnTfAaG1Lh8fL2EkP3CnOXKG+/uaqYbpCX8o9b+1k4i05g8bh5CO/p8 ePy+JdNkenuhqZ+/S53fP3OC/J4O4r7qT0g6RXSzA7MZ/BLUpTwwLPSFRMgGo15091oWL YmEl653xRDHWaE0FHI0OzpsJ3yBYHZEyYT0NZc9cwR4IkOpqmXaKxvbWdTSeWs4Nn0w== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794404635; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=F21HXehkhHOJ2Hcvkr+Y1EVk7iSfQoJREPt1VKE3m9I=; b=2xyWqcM1MRb2qamkP/xpSCUN/LKMIqMSSsaUvG6HbAzFfvAaRftDsnu/NuvpO0QTOd5n J+/iA/x777kMDUHsXvwz0Qhlh2HofYm8fGbHyNTv9/FlPDrHVQPGA5ZtiyTHdnbI44S/g ehBfWwdo//BVH54nKa24MytpmUsBqBu3ZZvTdpVoOdxWliSeB8cru+5WDzG3CiPv6z/lT 9iBdZfOUsRdr4/Q0E78esu7n01xbqyVmI+oupEhvXC4+dtci6G9XKWWzcgbp6kQDisjxI fiDN6VcIwnAsyD5xKsc0KZDsK+ZnWPNutD54wP6wkK6Z3NbpelRWGKPlcINIJLMhe+g== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=aAqse8ef; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 68D8A606A327 for ; Wed, 11 Nov 2026 13:43:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=aAqse8ef Received: by smtp.kernel.org (Postfix) with ESMTPSA id 351D71F00A05; Wed, 11 Nov 2026 13:43:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794404635; bh=F21HXehkhHOJ2Hcvkr+Y1EVk7iSfQoJREPt1VKE3m9I=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=aAqse8ef9sE588ha03+UPpRxfY+8N4FSCj00v38AvDX9hKkpmz07G/8v1NhE9dwIF WXhM8zhR17mq+7jWWEmJHVb3NqNIFfe8LHaRjSCQdlg8xNUAHpmJTdeH8xcUSGkc0c voJxG9panXqSFsE526H4gzhduFK+mMy+jTnUaeu0vyTVy5pep4EK9nkWdNnkBujx+F sf+FBlKdtc1KuP41fuJ5Ri1kolFPRYDzfO/5eipeN4W34dMKxgm2ww0oQhrbz4Fx0S uOP4XXSDM0TPwBmyyIntSKR/3dHm9e2pIJtNCP82cDqzPcjxjO0u2uwUqhvEnpurPF 3hI58yDKnveMA== From: Sasha Levin To: stable@vger.kernel.org Cc: Oleg Nesterov , stable@kernel.org, syzbot+0a4c46806941297fecb9@syzkaller.appspotmail.com, Kusaram Devineni , Kees Cook , Sasha Levin Subject: [PATCH 6.6.y] signalfd: don't dequeue the forced fatal signals Date: Wed, 11 Nov 2026 08:43:52 -0500 Message-ID: <20261111134326.1683124-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261107052941-failed-6.6-d72e0fb3b00c@kernel.org> References: <20261107052941-failed-6.6-d72e0fb3b00c@kernel.org> X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Oleg Nesterov [ Upstream commit d72e0fb3b00c6a1146bcfd7186ad9f6f609ba236 ] These signals should act like SIGKILL, in that userspace must never dequeue them. But as Kusaram explains, io_uring-driven signalfd_read_iter() called from get_signal() -> task_work_run() paths can do this before get_signal() has a chance to dequeue such a signal and notice SA_IMMUTABLE. Change signalfd_poll() and signalfd_dequeue() to add pending SA_IMMUTABLE signals to ctx->sigmask. TODO: we should probably change force_sig_info_to_task(HANDLER_EXIT) to make fatal_signal_pending() true, or add a fatal_or_forced_signal_pending() helper. Then signalfd_dequeue() could just return -EINTR in this case. This also makes sense for get_signal(), which could prioritize a fatal signal sent by (say) force_sig_seccomp(force_coredump => true), just like it already prioritizes SIGKILL. Cc: stable@kernel.org Reported-by: syzbot+0a4c46806941297fecb9@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=0a4c46806941297fecb9 Tested-by: syzbot+0a4c46806941297fecb9@syzkaller.appspotmail.com Link: https://lore.kernel.org/all/69d122fd.050a0220.2dbe29.001c.GAE@google.com/ Suggested-by: Kusaram Devineni Signed-off-by: Oleg Nesterov Reviewed-by: Kees Cook Link: https://patch.msgid.link/adO3HG8bvwRPcmte@redhat.com Signed-off-by: Kees Cook [ sashal: Retained current as the first argument to both dequeue_signal() calls to match the existing API. ] Signed-off-by: Sasha Levin --- fs/signalfd.c | 28 ++++++++++++++++++++++------ 1 file changed, 22 insertions(+), 6 deletions(-) diff --git a/fs/signalfd.c b/fs/signalfd.c index e20d1484c6633..797c906bb5de1 100644 --- a/fs/signalfd.c +++ b/fs/signalfd.c @@ -48,17 +48,30 @@ static int signalfd_release(struct inode *inode, struct file *file) return 0; } +static void refine_sigmask(struct signalfd_ctx *ctx, sigset_t *sigmask) +{ + struct k_sigaction *k = current->sighand->action; + int n; + + *sigmask = ctx->sigmask; + for (n = 1; n <= _NSIG; ++n, ++k) { + if (k->sa.sa_flags & SA_IMMUTABLE) + sigaddset(sigmask, n); + } +} + static __poll_t signalfd_poll(struct file *file, poll_table *wait) { struct signalfd_ctx *ctx = file->private_data; __poll_t events = 0; + sigset_t sigmask; poll_wait(file, ¤t->sighand->signalfd_wqh, wait); spin_lock_irq(¤t->sighand->siglock); - if (next_signal(¤t->pending, &ctx->sigmask) || - next_signal(¤t->signal->shared_pending, - &ctx->sigmask)) + refine_sigmask(ctx, &sigmask); + if (next_signal(¤t->pending, &sigmask) || + next_signal(¤t->signal->shared_pending, &sigmask)) events |= EPOLLIN; spin_unlock_irq(¤t->sighand->siglock); @@ -156,11 +169,13 @@ static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, kernel_siginfo_t *info int nonblock) { enum pid_type type; - ssize_t ret; DECLARE_WAITQUEUE(wait, current); + sigset_t sigmask; + ssize_t ret; spin_lock_irq(¤t->sighand->siglock); - ret = dequeue_signal(current, &ctx->sigmask, info, &type); + refine_sigmask(ctx, &sigmask); + ret = dequeue_signal(current, &sigmask, info, &type); switch (ret) { case 0: if (!nonblock) @@ -175,7 +190,7 @@ static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, kernel_siginfo_t *info add_wait_queue(¤t->sighand->signalfd_wqh, &wait); for (;;) { set_current_state(TASK_INTERRUPTIBLE); - ret = dequeue_signal(current, &ctx->sigmask, info, &type); + ret = dequeue_signal(current, &sigmask, info, &type); if (ret != 0) break; if (signal_pending(current)) { @@ -185,6 +200,7 @@ static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, kernel_siginfo_t *info spin_unlock_irq(¤t->sighand->siglock); schedule(); spin_lock_irq(¤t->sighand->siglock); + refine_sigmask(ctx, &sigmask); } spin_unlock_irq(¤t->sighand->siglock); -- 2.53.0