From: Chen Linxuan <[email protected]> Split namespace acquisition from namespace fd creation and represent a privileged target task as a scoped class that owns both the task reference and exec_update_lock. Use the class for namespace lookups so ptrace access checks and task state reads remain tied to the same exec critical section, while open_namespace() stays outside the lock.
Assisted-by: LLM Signed-off-by: Chen Linxuan <[email protected]> --- fs/pidfs.c | 115 ++++++++++++++++++++++++++++++++++++++----------------------- 1 file changed, 71 insertions(+), 44 deletions(-) diff --git a/fs/pidfs.c b/fs/pidfs.c index a6a643f15d08..49a1ab0c42f9 100644 --- a/fs/pidfs.c +++ b/fs/pidfs.c @@ -527,62 +527,67 @@ static bool pidfs_ioctl_valid(unsigned int cmd) return false; } -static long pidfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg) +static inline void pidfd_put_task_locked(struct task_struct *task) { - struct task_struct *task __free(put_task) = NULL; - struct nsproxy *nsp __free(put_nsproxy) = NULL; - struct ns_common *ns_common = NULL; - int error; - - if (!pidfs_ioctl_valid(cmd)) - return -ENOIOCTLCMD; - - if (cmd == FS_IOC_GETVERSION) { - if (!arg) - return -EINVAL; - - __u32 __user *argp = (__u32 __user *)arg; - return put_user(file_inode(file)->i_generation, argp); + if (!IS_ERR_OR_NULL(task)) { + up_read(&task->signal->exec_update_lock); + put_task_struct(task); } +} - /* Extensible IOCTL that does not open namespace FDs, take a shortcut */ - if (_IOC_NR(cmd) == _IOC_NR(PIDFD_GET_INFO)) - return pidfd_info(file, cmd, arg); +/* + * Return @pid's task with @task's exec_update_lock held. The ptrace check + * and the callers' task state lookup must be performed while the lock is held + * so that they cannot race with a concurrent execve(). + */ +static struct task_struct *pidfd_get_task_locked(struct pid *pid, + unsigned long arg) +{ + struct task_struct *task __free(put_task) = + get_pid_task(pid, PIDTYPE_PID); + int error; - task = get_pid_task(pidfd_pid(file), PIDTYPE_PID); if (!task) - return -ESRCH; + return ERR_PTR(-ESRCH); if (arg) - return -EINVAL; + return ERR_PTR(-EINVAL); - /* - * We're trying to open a file descriptor to the namespace so perform a - * filesystem cred ptrace check. Hold @task's exec_update_lock for the - * duration of the ptrace check and the namespace lookup so that the - * credentials used for the access decision match those of @task at the - * time its namespace is read, preventing a concurrent execve() from - * swapping the task's credentials in between the check and the use. We - * mirror nsfs behavior. - */ error = down_read_killable(&task->signal->exec_update_lock); if (error) - return error; + return ERR_PTR(error); if (!ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS)) { - error = -EACCES; - goto out_unlock; + up_read(&task->signal->exec_update_lock); + return ERR_PTR(-EACCES); } + return_ptr(task); +} + +DEFINE_CLASS(pidfd_task_locked, struct task_struct *, + pidfd_put_task_locked(_T), + pidfd_get_task_locked(pid, arg), + struct pid *pid, unsigned long arg) + +static struct ns_common *pidfd_get_namespace(struct pid *pid, + unsigned int cmd, + unsigned long arg) +{ + struct nsproxy *nsp __free(put_nsproxy) = NULL; + struct ns_common *ns_common = NULL; + + CLASS(pidfd_task_locked, task)(pid, arg); + if (IS_ERR(task)) + return ERR_CAST(task); + scoped_guard(task_lock, task) { nsp = task->nsproxy; if (nsp) get_nsproxy(nsp); } - if (!nsp) { - error = -ESRCH; /* just pretend it didn't exist */ - goto out_unlock; - } + if (!nsp) + return ERR_PTR(-ESRCH); /* just pretend it didn't exist */ switch (cmd) { /* Namespaces that hang of nsproxy. */ @@ -664,16 +669,38 @@ static long pidfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg) #endif break; default: - error = -ENOIOCTLCMD; + return ERR_PTR(-ENOIOCTLCMD); } - if (!error && !ns_common) - error = -EOPNOTSUPP; + if (!ns_common) + return ERR_PTR(-EOPNOTSUPP); -out_unlock: - up_read(&task->signal->exec_update_lock); - if (error) - return error; + return ns_common; +} + +static long pidfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg) +{ + struct ns_common *ns_common = NULL; + + if (!pidfs_ioctl_valid(cmd)) + return -ENOIOCTLCMD; + + if (cmd == FS_IOC_GETVERSION) { + if (!arg) + return -EINVAL; + + __u32 __user *argp = (__u32 __user *)arg; + + return put_user(file_inode(file)->i_generation, argp); + } + + /* Extensible IOCTL that does not open namespace FDs, take a shortcut */ + if (_IOC_NR(cmd) == _IOC_NR(PIDFD_GET_INFO)) + return pidfd_info(file, cmd, arg); + + ns_common = pidfd_get_namespace(pidfd_pid(file), cmd, arg); + if (IS_ERR(ns_common)) + return PTR_ERR(ns_common); /* open_namespace() unconditionally consumes the reference */ return open_namespace(ns_common); -- 2.53.0
