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 D449C253944; Tue, 11 Nov 2025 01:04:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762823089; cv=none; b=nXD5x766AK9n7QJUJtEQK2p/AuxLhTyKLoquTWzhskpberj9N7is1X6NZiOPCX68RfhFkXOgnWmkG5+EegnQnofAlLOdoBA1HUj+WdxVKLcPTBaMNArW4forXm+WPQGgx98WjqvvIrkDW4vdTDQBtoKLObYg+CeU90ft587P+nI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762823089; c=relaxed/simple; bh=XGr202lKgCT+hN1/hynnVt2ZswvwCJMpn0JTgqhuP2g=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=XGMq+prvH8sjmFsQdlyGPEriZQTVAebs8UGtz7Ia49earzbZFUheE1JO/PJFVIaIa4/iXRRbCuhZKqYI5QRvw/ZCAMcnme2RSdIR4owJrlUksTzlmp294VWOHVqei9tYta4x2oDnP9Q7EI1Ob/a864Sd8sRBFvcV5aNuCdaJ7xY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=U+qT3U+X; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="U+qT3U+X" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 60F6BC19425; Tue, 11 Nov 2025 01:04:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1762823089; bh=XGr202lKgCT+hN1/hynnVt2ZswvwCJMpn0JTgqhuP2g=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=U+qT3U+XxVqYYUYAQvMfm/7V1ieGhiDDzZF6c7haRfY/DCIkQm4vYHFZhCmflenr5 8RR+cNP3GUAZqmApTgo7HZt8xqS8F9+7vcnmg4SpPvpMqGzLSUcWTzyKDlywPGil1l LcDQ9zJeqgudED4y/rjVDEsf32gbA/2eloYF5pk0= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Jann Horn , Pranav Tyagi , Thomas Gleixner , Sasha Levin Subject: [PATCH 6.12 147/565] futex: Dont leak robust_list pointer on exec race Date: Tue, 11 Nov 2025 09:40:03 +0900 Message-ID: <20251111004530.246286248@linuxfoundation.org> X-Mailer: git-send-email 2.51.2 In-Reply-To: <20251111004526.816196597@linuxfoundation.org> References: <20251111004526.816196597@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Pranav Tyagi [ Upstream commit 6b54082c3ed4dc9821cdf0edb17302355cc5bb45 ] sys_get_robust_list() and compat_get_robust_list() use ptrace_may_access() to check if the calling task is allowed to access another task's robust_list pointer. This check is racy against a concurrent exec() in the target process. During exec(), a task may transition from a non-privileged binary to a privileged one (e.g., setuid binary) and its credentials/memory mappings may change. If get_robust_list() performs ptrace_may_access() before this transition, it may erroneously allow access to sensitive information after the target becomes privileged. A racy access allows an attacker to exploit a window during which ptrace_may_access() passes before a target process transitions to a privileged state via exec(). For example, consider a non-privileged task T that is about to execute a setuid-root binary. An attacker task A calls get_robust_list(T) while T is still unprivileged. Since ptrace_may_access() checks permissions based on current credentials, it succeeds. However, if T begins exec immediately afterwards, it becomes privileged and may change its memory mappings. Because get_robust_list() proceeds to access T->robust_list without synchronizing with exec() it may read user-space pointers from a now-privileged process. This violates the intended post-exec access restrictions and could expose sensitive memory addresses or be used as a primitive in a larger exploit chain. Consequently, the race can lead to unauthorized disclosure of information across privilege boundaries and poses a potential security risk. Take a read lock on signal->exec_update_lock prior to invoking ptrace_may_access() and accessing the robust_list/compat_robust_list. This ensures that the target task's exec state remains stable during the check, allowing for consistent and synchronized validation of credentials. Suggested-by: Jann Horn Signed-off-by: Pranav Tyagi Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/linux-fsdevel/1477863998-3298-5-git-send-email-jann@thejh.net/ Link: https://github.com/KSPP/linux/issues/119 Signed-off-by: Sasha Levin --- kernel/futex/syscalls.c | 106 +++++++++++++++++++++------------------- 1 file changed, 56 insertions(+), 50 deletions(-) diff --git a/kernel/futex/syscalls.c b/kernel/futex/syscalls.c index 4b6da9116aa6c..880c9bf2f3150 100644 --- a/kernel/futex/syscalls.c +++ b/kernel/futex/syscalls.c @@ -39,6 +39,56 @@ SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head, return 0; } +static inline void __user *futex_task_robust_list(struct task_struct *p, bool compat) +{ +#ifdef CONFIG_COMPAT + if (compat) + return p->compat_robust_list; +#endif + return p->robust_list; +} + +static void __user *futex_get_robust_list_common(int pid, bool compat) +{ + struct task_struct *p = current; + void __user *head; + int ret; + + scoped_guard(rcu) { + if (pid) { + p = find_task_by_vpid(pid); + if (!p) + return (void __user *)ERR_PTR(-ESRCH); + } + get_task_struct(p); + } + + /* + * Hold exec_update_lock to serialize with concurrent exec() + * so ptrace_may_access() is checked against stable credentials + */ + ret = down_read_killable(&p->signal->exec_update_lock); + if (ret) + goto err_put; + + ret = -EPERM; + if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS)) + goto err_unlock; + + head = futex_task_robust_list(p, compat); + + up_read(&p->signal->exec_update_lock); + put_task_struct(p); + + return head; + +err_unlock: + up_read(&p->signal->exec_update_lock); +err_put: + put_task_struct(p); + return (void __user *)ERR_PTR(ret); +} + /** * sys_get_robust_list() - Get the robust-futex list head of a task * @pid: pid of the process [zero for current task] @@ -49,36 +99,14 @@ SYSCALL_DEFINE3(get_robust_list, int, pid, struct robust_list_head __user * __user *, head_ptr, size_t __user *, len_ptr) { - struct robust_list_head __user *head; - unsigned long ret; - struct task_struct *p; - - rcu_read_lock(); - - ret = -ESRCH; - if (!pid) - p = current; - else { - p = find_task_by_vpid(pid); - if (!p) - goto err_unlock; - } - - ret = -EPERM; - if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS)) - goto err_unlock; + struct robust_list_head __user *head = futex_get_robust_list_common(pid, false); - head = p->robust_list; - rcu_read_unlock(); + if (IS_ERR(head)) + return PTR_ERR(head); if (put_user(sizeof(*head), len_ptr)) return -EFAULT; return put_user(head, head_ptr); - -err_unlock: - rcu_read_unlock(); - - return ret; } long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout, @@ -455,36 +483,14 @@ COMPAT_SYSCALL_DEFINE3(get_robust_list, int, pid, compat_uptr_t __user *, head_ptr, compat_size_t __user *, len_ptr) { - struct compat_robust_list_head __user *head; - unsigned long ret; - struct task_struct *p; - - rcu_read_lock(); - - ret = -ESRCH; - if (!pid) - p = current; - else { - p = find_task_by_vpid(pid); - if (!p) - goto err_unlock; - } - - ret = -EPERM; - if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS)) - goto err_unlock; + struct compat_robust_list_head __user *head = futex_get_robust_list_common(pid, true); - head = p->compat_robust_list; - rcu_read_unlock(); + if (IS_ERR(head)) + return PTR_ERR(head); if (put_user(sizeof(*head), len_ptr)) return -EFAULT; return put_user(ptr_to_compat(head), head_ptr); - -err_unlock: - rcu_read_unlock(); - - return ret; } #endif /* CONFIG_COMPAT */ -- 2.51.0