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t=1789998363; bh=XK+vFPcoNOWpEsInXI2i4g3mZjN5dJruLtFC6744UCg=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=Aj1MZ6b0DckcbN8ZWhMcy3sQmM5nKsMEjWSoa3mKzl4IzTTdqYMEkUXOnPbs/V8z1 Mx4jZ9zAiATVYJt5FPaI8JLIJKQrvVpq0b+xhEky4JsfoHwxRqlljaIeQYJlALdHJy 4gXFul/htFtIbwAHHvJ7UFvWrIEfQwsVShk8nfiSPeJTeyzDDh2P/QlvKGFh9Fg9ys ho6lcgL2qG881lUJPTANEunTFLV+Mi6Z+65BhopjaMu7+eyZY4ncZAu/A8vkwRE017 Jdsab31+dou4Pm1UlIjSVp5JFnPRrUoXRpUiIkO2yuS/6kDm+mP4AdzUBBPFat3VVz sLGUqsBTeskMA== From: Christian Brauner Date: Mon, 21 Sep 2026 15:45:05 +0200 Subject: [PATCH v3 16/17] signal: enforce the user worker signal mask in __set_task_blocked() MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260921-work-coredump-fixes-v3-16-8e4adb1619e6@kernel.org> References: <20260921-work-coredump-fixes-v3-0-8e4adb1619e6@kernel.org> In-Reply-To: <20260921-work-coredump-fixes-v3-0-8e4adb1619e6@kernel.org> To: Oleg Nesterov , Chris Mason , linux-fsdevel@vger.kernel.org Cc: Jens Axboe , Alexander Viro , Jan Kara , NeilBrown , Ingo Molnar , Peter Zijlstra , linux-mm@kvack.org, io-uring@vger.kernel.org, "Christian Brauner (Amutable)" X-Mailer: b4 0.17-dev-db0b7 X-Developer-Signature: v=1; a=openpgp-sha256; l=2674; i=brauner@kernel.org; h=from:subject:message-id; bh=N9+t6kg9G5schzNoEgToZQtBo5+eN+aMw/ZqCZtP+xs=; b=owGbwMvMwCU28Zj0gdSKO4sYT6slMWRtNLm7ceqfa/vOperqasXWKHp+9/O/vtt16TmBg9pyW /pKTn9h7ShlYRDjYpAVU2RxaDcJl1vOU7HZKFMDZg4rE8gQBi5OAZhIUQnD/xy1itCSJL+A5vvr bc6IHL/CpDexIOn7wa2JkpYVJu8LNjH801vYraC/epZrb8Lti8vr70eH/N73ct8GxiZ2sbvaHq3 X+AA= X-Developer-Key: i=brauner@kernel.org; a=openpgp; fpr=4880B8C9BD0E5106FC070F4F7B3C391EFEA93624 X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 562B02000A X-Stat-Signature: 7tkytysa1afwr4cczj4rbixawn9wcweg X-Rspam-User: X-HE-Tag: 1789998364-88014 X-HE-Meta: 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 0fxk0Cah pYtw6YxOz6BnKAkBWKa/PVkx7DFdJMSRT7++l7NGTPe0zGG55kZ3XvOwcwajFieYwTMI9fl9Q0BpQN39Gh+v2G1/0DLPL6YOv/HsdD5ossy6s3eOQ/b2vZshu89vc4rAsNOvUJ37TZdQpcyuc2QjkWMFa1a3FSGaAdBpPqoULW/CcmHqkuaTjftrFBD6TqKW0xS/Lo0x1oFSvSCbVaareuCekdCROLCEQZsx+/g5AjAErgsVP7STSi4bTDBPil3UTKEY042T8q+GKatEzA3ztQm6CRKXt2loPDZ9WYlLaVYwJ2wSWrSjcjZqKow== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: User workers block every signal except for SIGKILL and SIGSTOP in copy_process(). So complete_signal() never picks a thread that blocks the signal and get_signal() never dequeues such a thread. Net effect is that user workers only exit on SIGKILL or stop on SIGSTOP. Before we fixed it a tracer could unblock a signal. For example, by unblocking SIGHUP a installing a handler complete_signal() could end up picking a user worker for a process-directed SIGHUP. Which effectively means the handler never runs. After blocking PTRACE_SETSIGMASK what remains is the in-kernel sigprocmask() and force_sig_info_to_task() changes. The in-kernel sigprocmask() users block more signals for a critical section and restore the saved mask afterwards. cifs used to do that in __smb_send_rqst() and ocfs2 in ocfs2_block_signals(). Both were reachable from an io-wq worker. Both only add SIGKILL and SIGSTOP to the user workers's and then put the fork-time mask back. force_sig_info_to_task() unblocks a signal so a target can't hide from the signal. A synchronous signal forced onto a user worker is accepted currently so let's leave that alone. Make it a rule that a user worker's signal mask can never drop below the copy_process() deafult. SIGKILL and SIGSTOP have the same rule in the other direction. rt_sigprocmask(), set_current_blocked() and PTRACE_SETSIGMASK strip them from whatever mask userspace asks for. Do the same for user worker mask in __set_task_blocked(). Add the fork-time mask back into the new set for a user worker and warn if that changed anything. Warn when a caller unblocks a signal for a user worker. No functional changes. Link: https://lore.kernel.org/r/aq_4fY6GVtK47Njq@redhat.com Signed-off-by: Christian Brauner (Amutable) --- kernel/signal.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/kernel/signal.c b/kernel/signal.c index c3bad983dd37..137002445b0d 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -3212,6 +3212,16 @@ long do_no_restart_syscall(struct restart_block *param) static void __set_task_blocked(struct task_struct *tsk, const sigset_t *newset) { + sigset_t floor, floored; + + /* A user worker never unblocks anything but SIGKILL and SIGSTOP. */ + if (unlikely(tsk->flags & PF_USER_WORKER)) { + siginitsetinv(&floor, SIG_KERNEL_ONLY_MASK); + sigorsets(&floored, newset, &floor); + WARN_ON_ONCE(!sigequalsets(&floored, newset)); + newset = &floored; + } + if (task_sigpending(tsk) && !thread_group_empty(tsk)) { sigset_t newblocked; /* A set of now blocked but previously unblocked signals. */ -- 2.53.0