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authorChristian Brauner <brauner@kernel.org>2023-03-27 20:22:51 +0200
committerChristian Brauner <brauner@kernel.org>2023-04-03 11:16:56 +0200
commit6ae930d9dbf2d093157be33428538c91966d8a9f (patch)
treea89117e5612341376fc147f26b9715c47013d27d /kernel/fork.c
parent197b6b60ae7bc51dd0814953c562833143b292aa (diff)
pid: add pidfd_prepare()
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: Jan Kara <jack@suse.cz> Message-Id: <20230327-pidfd-file-api-v1-1-5c0e9a3158e4@kernel.org> Signed-off-by: Christian Brauner <brauner@kernel.org>
Diffstat (limited to 'kernel/fork.c')
-rw-r--r--kernel/fork.c85
1 files changed, 85 insertions, 0 deletions
diff --git a/kernel/fork.c b/kernel/fork.c
index c0257cbee093..a34395bd708a 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1951,6 +1951,91 @@ 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);