From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A2E44AD23 for ; Thu, 27 Oct 2022 17:07:07 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EE921C433C1; Thu, 27 Oct 2022 17:07:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1666890427; bh=KnqdBqXpwjnoczNNin28/Qu7T5+d3J3wqw/aPVgwV5I=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=M6gkwDRq0ZzW/1wjsK67lKou40T33TVnreVpyu07Srkg2xJGTGA9FB1KrmtyIVOKA rSp0/RiFPQ9T5igRiiYFZ8Xe5FTQNSX1hJC+/r83GuFjNS8SlzrZ6GXEtmSWuDpSLR f/xEYcoJCYAy853/om+k78fumLtbSSuciB4dmKDQ= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Jeff Layton , "J. Bruce Fields" , Alexander Viro , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Cyrill Gorcunov , Andrei Vagin , Pavel Tikhomirov , Sasha Levin Subject: [PATCH 5.10 67/79] fcntl: make F_GETOWN(EX) return 0 on dead owner task Date: Thu, 27 Oct 2022 18:56:17 +0200 Message-Id: <20221027165056.588648208@linuxfoundation.org> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20221027165054.270676357@linuxfoundation.org> References: <20221027165054.270676357@linuxfoundation.org> User-Agent: quilt/0.67 Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Pavel Tikhomirov [ Upstream commit cc4a3f885e8f2bc3c86a265972e94fef32d68f67 ] Currently there is no way to differentiate the file with alive owner from the file with dead owner but pid of the owner reused. That's why CRIU can't actually know if it needs to restore file owner or not, because if it restores owner but actual owner was dead, this can introduce unexpected signals to the "false"-owner (which reused the pid). Let's change the api, so that F_GETOWN(EX) returns 0 in case actual owner is dead already. This comports with the POSIX spec, which states that a PID of 0 indicates that no signal will be sent. Cc: Jeff Layton Cc: "J. Bruce Fields" Cc: Alexander Viro Cc: linux-fsdevel@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: Cyrill Gorcunov Cc: Andrei Vagin Signed-off-by: Pavel Tikhomirov Signed-off-by: Jeff Layton Stable-dep-of: f671a691e299 ("fcntl: fix potential deadlocks for &fown_struct.lock") Signed-off-by: Sasha Levin --- fs/fcntl.c | 19 +++++++++++++------ 1 file changed, 13 insertions(+), 6 deletions(-) diff --git a/fs/fcntl.c b/fs/fcntl.c index 71b43538fa44..5a56351f1fc3 100644 --- a/fs/fcntl.c +++ b/fs/fcntl.c @@ -148,11 +148,15 @@ void f_delown(struct file *filp) pid_t f_getown(struct file *filp) { - pid_t pid; + pid_t pid = 0; read_lock(&filp->f_owner.lock); - pid = pid_vnr(filp->f_owner.pid); - if (filp->f_owner.pid_type == PIDTYPE_PGID) - pid = -pid; + rcu_read_lock(); + if (pid_task(filp->f_owner.pid, filp->f_owner.pid_type)) { + pid = pid_vnr(filp->f_owner.pid); + if (filp->f_owner.pid_type == PIDTYPE_PGID) + pid = -pid; + } + rcu_read_unlock(); read_unlock(&filp->f_owner.lock); return pid; } @@ -200,11 +204,14 @@ static int f_setown_ex(struct file *filp, unsigned long arg) static int f_getown_ex(struct file *filp, unsigned long arg) { struct f_owner_ex __user *owner_p = (void __user *)arg; - struct f_owner_ex owner; + struct f_owner_ex owner = {}; int ret = 0; read_lock(&filp->f_owner.lock); - owner.pid = pid_vnr(filp->f_owner.pid); + rcu_read_lock(); + if (pid_task(filp->f_owner.pid, filp->f_owner.pid_type)) + owner.pid = pid_vnr(filp->f_owner.pid); + rcu_read_unlock(); switch (filp->f_owner.pid_type) { case PIDTYPE_PID: owner.type = F_OWNER_TID; -- 2.35.1