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 0C7A9340D90; Wed, 3 Dec 2025 16:22:52 +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=1764778972; cv=none; b=P9EyfsbdUuPoqNlI5TwQ5qHd145oBOSu8bCTqt1dRUsmqULSyBMisxYCCftQ5ctAkSbz82wAAPYfXv+ex8pqqyYUU2VDnPvIdkfFIazkzM5IcUaguEmVSQnfT/iiTXQLN0QXPzOjAWMlQDU7jYbTyKOVBLa2FyfQVpMy1tpTa1w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764778972; c=relaxed/simple; bh=jpIjWsmDwTMZ/W8ihHZC1g57auSypON0DZ5Hkw+fQQU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=gbrfxzHrTOUPH3NfGw6hB5ZEnx+DmatNcJZUt7/XyG3UGNqxPqB3Iy2vgXoXDJhHTFP5dNOlAs28KGA1yp2Xad9MD1AqqQYGfNsluP91RB+BJQgjZGnPIbp00gTp2RdyX6awTkEyBlMQG7oqYb32supKjvG6ABFqJ8BTOe5kPy4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=xkJuZQaW; 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="xkJuZQaW" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 54A25C4CEF5; Wed, 3 Dec 2025 16:22:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1764778971; bh=jpIjWsmDwTMZ/W8ihHZC1g57auSypON0DZ5Hkw+fQQU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=xkJuZQaW0pqV/CquS/M0QnZl4UVyU+7XzoS/6t5HKymDrxQVjS0FM3ppgYVMfe/Q+ IKC4bhSdMtxOaWnuWZu5UQ8JODaOPoQyWKiNZfzeuu74ErpKo+6ZB6Lswg2crSZ7Me mD+U30q6SFSvoT7mc3jp9IaXo1b/ae8RQ2el9p/o= 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 6.1 117/568] futex: Dont leak robust_list pointer on exec race Date: Wed, 3 Dec 2025 16:21:59 +0100 Message-ID: <20251203152445.020050228@linuxfoundation.org> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20251203152440.645416925@linuxfoundation.org> References: <20251203152440.645416925@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 6.1-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 a8074079b09e8..48feaa545b3c7 100644 --- a/kernel/futex/syscalls.c +++ b/kernel/futex/syscalls.c @@ -40,6 +40,56 @@ 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] @@ -50,36 +100,14 @@ 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, @@ -322,36 +350,14 @@ 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