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Commit 0a841d0a authored by Christian Brauner's avatar Christian Brauner Committed by Greg Kroah-Hartman
Browse files

pid: add pidfd_prepare() 



commit 6ae930d9dbf2d093157be33428538c91966d8a9f upstream.

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.

Reviewed-by: default avatarJan Kara <jack@suse.cz>
Message-Id: <20230327-pidfd-file-api-v1-1-5c0e9a3158e4@kernel.org>
Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 53df781e

include/linux/pid.h

+1 −0
Original line number Diff line number Diff line
@@ -75,6 +75,7 @@ extern const struct file_operations pidfd_fops; 
struct file;



extern struct pid *pidfd_pid(const struct file *file);

int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret);



static inline struct pid *get_pid(struct pid *pid)

{

kernel/fork.c

+85 −0
Original line number Diff line number Diff line
@@ -1750,6 +1750,91 @@ const struct file_operations pidfd_fops = { 
#endif

};



/**

 * __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.



 * The helper doesn't perform checks on @pid which makes it useful for pidfds

 * created via CLONE_PIDFD where @pid has no task attached when the pidfd and

 * pidfd file are prepared.

 *

 * 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.

 */

static int __pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret)

{

	int pidfd;

	struct file *pidfd_file;



	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_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.

 *

 * The helper verifies that @pid is used as a thread group leader.

 *

 * 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)

{

	if (!pid || !pid_has_task(pid, PIDTYPE_TGID))

		return -EINVAL;



	return __pidfd_prepare(pid, flags, ret);

}



static void __delayed_free_task(struct rcu_head *rhp)

{

	struct task_struct *tsk = container_of(rhp, struct task_struct, rcu);