[1/3] pid: add pidfd_prepare()
Commit Message
Add a new helper that allows to reserve a pidfd and allocates a new
pidfd file that stashes the provided struct pid. This will allow us to
remove places that either open code this function or that call
pidfd_create() but then have to call close_fd() because there are still
failure points after pidfd_create() has been called.
Signed-off-by: Christian Brauner <brauner@kernel.org>
---
include/linux/pid.h | 1 +
kernel/pid.c | 69 +++++++++++++++++++++++++++++++++++++++++++----------
2 files changed, 58 insertions(+), 12 deletions(-)
Comments
On Mon 27-03-23 20:22:51, Christian Brauner wrote:
> Add a new helper that allows to reserve a pidfd and allocates a new
> pidfd file that stashes the provided struct pid. This will allow us to
> remove places that either open code this function or that call
> pidfd_create() but then have to call close_fd() because there are still
> failure points after pidfd_create() has been called.
>
> Signed-off-by: Christian Brauner <brauner@kernel.org>
Looks good to me. Feel free to add:
Reviewed-by: Jan Kara <jack@suse.cz>
Honza
> ---
> include/linux/pid.h | 1 +
> kernel/pid.c | 69 +++++++++++++++++++++++++++++++++++++++++++----------
> 2 files changed, 58 insertions(+), 12 deletions(-)
>
> diff --git a/include/linux/pid.h b/include/linux/pid.h
> index 343abf22092e..b75de288a8c2 100644
> --- a/include/linux/pid.h
> +++ b/include/linux/pid.h
> @@ -80,6 +80,7 @@ extern struct pid *pidfd_pid(const struct file *file);
> struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags);
> struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags);
> int pidfd_create(struct pid *pid, unsigned int flags);
> +int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret);
>
> static inline struct pid *get_pid(struct pid *pid)
> {
> diff --git a/kernel/pid.c b/kernel/pid.c
> index 3fbc5e46b721..95e7e01574c8 100644
> --- a/kernel/pid.c
> +++ b/kernel/pid.c
> @@ -576,6 +576,56 @@ struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags)
> return task;
> }
>
> +/**
> + * pidfd_prepare - allocate a new pidfd_file and reserve a pidfd
> + * @pid: the struct pid for which to create a pidfd
> + * @flags: flags of the new @pidfd
> + * @pidfd: the pidfd to return
> + *
> + * Allocate a new file that stashes @pid and reserve a new pidfd number in the
> + * caller's file descriptor table. The pidfd is reserved but not installed yet.
> + *
> + * If this function returns successfully the caller is responsible to either
> + * call fd_install() passing the returned pidfd and pidfd file as arguments in
> + * order to install the pidfd into its file descriptor table or they must use
> + * put_unused_fd() and fput() on the returned pidfd and pidfd file
> + * respectively.
> + *
> + * This function is useful when a pidfd must already be reserved but there
> + * might still be points of failure afterwards and the caller wants to ensure
> + * that no pidfd is leaked into its file descriptor table.
> + *
> + * Return: On success, a reserved pidfd is returned from the function and a new
> + * pidfd file is returned in the last argument to the function. On
> + * error, a negative error code is returned from the function and the
> + * last argument remains unchanged.
> + */
> +int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret)
> +{
> + int pidfd;
> + struct file *pidfd_file;
> +
> + if (!pid || !pid_has_task(pid, PIDTYPE_TGID))
> + return -EINVAL;
> +
> + if (flags & ~(O_NONBLOCK | O_RDWR | O_CLOEXEC))
> + return -EINVAL;
> +
> + pidfd = get_unused_fd_flags(O_RDWR | O_CLOEXEC);
> + if (pidfd < 0)
> + return pidfd;
> +
> + pidfd_file = anon_inode_getfile("[pidfd]", &pidfd_fops, pid,
> + flags | O_RDWR | O_CLOEXEC);
> + if (IS_ERR(pidfd_file)) {
> + put_unused_fd(pidfd);
> + return PTR_ERR(pidfd_file);
> + }
> + get_pid(pid); /* held by pidfd_file now */
> + *ret = pidfd_file;
> + return pidfd;
> +}
> +
> /**
> * pidfd_create() - Create a new pid file descriptor.
> *
> @@ -594,20 +644,15 @@ struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags)
> */
> int pidfd_create(struct pid *pid, unsigned int flags)
> {
> - int fd;
> + int pidfd;
> + struct file *pidfd_file;
>
> - if (!pid || !pid_has_task(pid, PIDTYPE_TGID))
> - return -EINVAL;
> -
> - if (flags & ~(O_NONBLOCK | O_RDWR | O_CLOEXEC))
> - return -EINVAL;
> -
> - fd = anon_inode_getfd("[pidfd]", &pidfd_fops, get_pid(pid),
> - flags | O_RDWR | O_CLOEXEC);
> - if (fd < 0)
> - put_pid(pid);
> + pidfd = pidfd_prepare(pid, flags, &pidfd_file);
> + if (pidfd < 0)
> + return pidfd;
>
> - return fd;
> + fd_install(pidfd, pidfd_file);
> + return pidfd;
> }
>
> /**
>
> --
> 2.34.1
>
@@ -80,6 +80,7 @@ extern struct pid *pidfd_pid(const struct file *file);
struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags);
struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags);
int pidfd_create(struct pid *pid, unsigned int flags);
+int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret);
static inline struct pid *get_pid(struct pid *pid)
{
@@ -576,6 +576,56 @@ struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags)
return task;
}
+/**
+ * pidfd_prepare - allocate a new pidfd_file and reserve a pidfd
+ * @pid: the struct pid for which to create a pidfd
+ * @flags: flags of the new @pidfd
+ * @pidfd: the pidfd to return
+ *
+ * Allocate a new file that stashes @pid and reserve a new pidfd number in the
+ * caller's file descriptor table. The pidfd is reserved but not installed yet.
+ *
+ * If this function returns successfully the caller is responsible to either
+ * call fd_install() passing the returned pidfd and pidfd file as arguments in
+ * order to install the pidfd into its file descriptor table or they must use
+ * put_unused_fd() and fput() on the returned pidfd and pidfd file
+ * respectively.
+ *
+ * This function is useful when a pidfd must already be reserved but there
+ * might still be points of failure afterwards and the caller wants to ensure
+ * that no pidfd is leaked into its file descriptor table.
+ *
+ * Return: On success, a reserved pidfd is returned from the function and a new
+ * pidfd file is returned in the last argument to the function. On
+ * error, a negative error code is returned from the function and the
+ * last argument remains unchanged.
+ */
+int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret)
+{
+ int pidfd;
+ struct file *pidfd_file;
+
+ if (!pid || !pid_has_task(pid, PIDTYPE_TGID))
+ return -EINVAL;
+
+ if (flags & ~(O_NONBLOCK | O_RDWR | O_CLOEXEC))
+ return -EINVAL;
+
+ pidfd = get_unused_fd_flags(O_RDWR | O_CLOEXEC);
+ if (pidfd < 0)
+ return pidfd;
+
+ pidfd_file = anon_inode_getfile("[pidfd]", &pidfd_fops, pid,
+ flags | O_RDWR | O_CLOEXEC);
+ if (IS_ERR(pidfd_file)) {
+ put_unused_fd(pidfd);
+ return PTR_ERR(pidfd_file);
+ }
+ get_pid(pid); /* held by pidfd_file now */
+ *ret = pidfd_file;
+ return pidfd;
+}
+
/**
* pidfd_create() - Create a new pid file descriptor.
*
@@ -594,20 +644,15 @@ struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags)
*/
int pidfd_create(struct pid *pid, unsigned int flags)
{
- int fd;
+ int pidfd;
+ struct file *pidfd_file;
- if (!pid || !pid_has_task(pid, PIDTYPE_TGID))
- return -EINVAL;
-
- if (flags & ~(O_NONBLOCK | O_RDWR | O_CLOEXEC))
- return -EINVAL;
-
- fd = anon_inode_getfd("[pidfd]", &pidfd_fops, get_pid(pid),
- flags | O_RDWR | O_CLOEXEC);
- if (fd < 0)
- put_pid(pid);
+ pidfd = pidfd_prepare(pid, flags, &pidfd_file);
+ if (pidfd < 0)
+ return pidfd;
- return fd;
+ fd_install(pidfd, pidfd_file);
+ return pidfd;
}
/**