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=1793227825; b=ltSdluDFB7KFbYdQ+hyf4YIHPszig9qKLVHB93uy1Dftk5jehRl21aGPo1zsIbNO5lVX 5ZfGqBtUpjqxz3ebD6Meq8JIfPeYMTW98dVLe9R46cSnO7q0AN4IMvtsLgzQXsnH8IfDV orUt8eSPZ0VFbMiacjqoc3b0ia2g0Gag1iiTBfkEQnQyJLGT/VzpikR6Sllfhm+PhRZpS z5djpSmv7LqTrqvdHMv16T3gja3YfOuPjKFPnKyPNIFLKrCvh50aRnVDtyFqGrpfiBejQ vabiywa/NdXe3gtEleolD9BjX1ppkSOCHFUMhYJkcCA187SWzZ4tSrxg1Vftg6TYefA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793227825; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=sLBkOKAo4Btus7+LZUplgPCWssAMm6YIDFeAEyJbIEU=; b=LK+NvoXuxFGC5WG8Bv4vXzaFrbaaOfSi9F1b89miKT3BwbKtfFtFaEu/wWP1DP3O9OvQ 4W9h9xJKZY7KS5wZcbpEX0QhugEYnDb6tPi7al+vvTuGPDzbANCDoPbJmvYzsQaKLwQzH L5oXGnrISeteW+MdIdSKfRaftwIyLBWUza+20ZcUxrc8dlOAMY93OpDQVinwqPzvpPf2L JuMSRsy4CoU/WARTYDQw80qRJsmhhyrMRTm/eYTQpIhjoC/bCUaSejIXi9CT/MjU7Cw60 UtKNHekRf+93x6tteVNh2+ux+BhtHp5G2/mVcw3mmwiLpDLvkHK162hjEDZZUX43YEQ== 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=BAIVXdEc; 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 A2BD6606A31D for ; Wed, 28 Oct 2026 22:50:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=BAIVXdEc Received: by smtp.kernel.org (Postfix) with ESMTPSA id B9D7E1F01825; Wed, 28 Oct 2026 22:50:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793227825; bh=sLBkOKAo4Btus7+LZUplgPCWssAMm6YIDFeAEyJbIEU=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=BAIVXdEcYlbG8vt8141nTgXlIWBqdP9jtnnhb5TyiDfMpn7ohEv49A4OrmIbfiftD Y6K1IGXM3HvK+2SItzSkqwc04ZVUboAjHNUras42/ZU/rbuvrBFLJTBe7IYK8wHRDz JH1qX+OlC7Lwx7rkm5tya5qM0N87XtUkXe33crG0CKzAUI5wKmUfwMjBFQGBgHgk7A ltY+TC9oE9J3fftUDjGczjJl+OprqlglIO4V2jahvlvJlmd1RFivFYyCD8Yjkn5sX/ HGR4bhkO//mKIDCzn9rwP3XNllL4c8Sx8u7sjDS5FD1iaJ1SRsHTLQmdUjjFlkMAu8 8HGqTXYECkEyQ== From: Sasha Levin To: stable@vger.kernel.org Cc: Christian Brauner , Oleg Nesterov , Sasha Levin Subject: [PATCH 6.6.y] coredump: prevent TIF_NOTIFY_SIGNAL from interrupting coredumps Date: Wed, 28 Oct 2026 18:50:23 -0400 Message-ID: <20261028225002.2428149-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026102819-progress-massager-b75a@gregkh> References: <2026102819-progress-massager-b75a@gregkh> 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: Christian Brauner [ Upstream commit a58d647acfdc62561f3570d114025b3bf38ae41b ] TIF_NOTIFY_SIGNAL is used to kick a task in uninterruptible sleep to return to userspace and run task work and then go back to sleep. This mechanism works well but breaks coredumps. dump_interrupted() only allows fatal signals to interrupt a coredump and the whole regular write path going to actual filesystems is impervious to TIF_NOTIFY_SIGNAL as well. However, both the usermodehelper pipe and the coredump socket will bail early on TIF_NOTIFY_SIGNAL. This affects the following codepaths: - coredump_sock_recv() -> unix_stream_read_generic() The request/ack handshake is abandoned before any coredump data is sent. - anon_pipe_write() returning -ERESTARTSYS Once the pipe is full this truncates the coredump. - unix_stream_sendmsg() returning -ERESTARTSYS Once the send buffer is full this truncates the coredump. - coredump_sock_wait() -> __kernel_read() This reports a failure that didn't happen. - wait_for_dump_helpers() -> wait_event_interruptible() This stops waiting for the coredump helpers. Such truncation is entirely invisible to userspace and all uapi bits still indicate that a successful coredump happened. A crashing process with a bunch of file backed mappings and io_uring thrown in loses most of the coredump data. If the NT_FILE note goes past PAGE_SIZE mappings it's gonzo. TIF_NOTIFY_SIGNAL is sent by io_uring for the common case. And it uses poll without sleeping so a completion callback runs task_work_add() from interrupt context against the task that submitted the request. This is the task that is running the coredump. Since that task hasn't set work_exited (it hasn't exited yet after all) TIF_NOTIFY_SIGNAL keeps reappearing. A coredumping task doesn't return to userspace. The task work is run at exit. So interrupting it doesn't buy anything and just loses the coredump which is quite valuable. Note that this isn't specific to io_uring. There's also klp_send_signals(), bpf_task_work_schedule_signal(), landlock's tsync and then technically, kthread_stop() and the printk kunit test set the bit raw. Link: https://patch.msgid.link/20260824-work-tif_notify_signal-v2-2-6609e42b3157@kernel.org Fixes: 12db8b690010 ("entry: Add support for TIF_NOTIFY_SIGNAL") Reviewed-by: Oleg Nesterov Cc: stable@vger.kernel.org Signed-off-by: Christian Brauner (Amutable) [ sashal: moved the guard from vfs_coredump() to do_coredump() before override_creds() ] Signed-off-by: Sasha Levin --- fs/coredump.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/fs/coredump.c b/fs/coredump.c index 326b30421eec3..cf0a41044d71f 100644 --- a/fs/coredump.c +++ b/fs/coredump.c @@ -642,6 +642,8 @@ void do_coredump(const kernel_siginfo_t *siginfo) if (retval < 0) goto fail_creds; + /* Task work must not cut the dump short, see signal_pending(). */ + guard(no_notify_signal)(); old_cred = override_creds(cred); ispipe = format_corename(&cn, &cprm, &argv, &argc); -- 2.53.0