The means by which a pid is determined from a pidfd is duplicated, with
some callers holding a reference to the (pid)fd, and others explicitly
pinning the pid.
Introduce __pidfd_get_pid() which abstracts both approaches and provide
optional output parameters for file->f_flags and the fd (the latter of
which, if provided, prevents the function from decrementing the fd's
refernce count).
Additionally, allow the ability to open a pidfd by opening a /proc/<pid>
directory, utilised by the pidfd_send_signal() system call, providing a
pidfd_get_pid_proc() helper function to do so.
Doing this allows us to eliminate open-coded pidfd pid lookup and to
consistently handle this in one place.
This lays the groundwork for a subsequent patch which adds a new sentinel
pidfd to explicitly reference the current process (i.e. thread group
leader) without the need for a pidfd.
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
---
include/linux/pid.h | 42 +++++++++++++++++++++++++++++++-
kernel/pid.c | 58 ++++++++++++++++++++++++++++++---------------
kernel/signal.c | 22 ++++-------------
3 files changed, 84 insertions(+), 38 deletions(-)
diff --git a/include/linux/pid.h b/include/linux/pid.h
index a3aad9b4074c..68b02eab7509 100644
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -2,6 +2,7 @@
#ifndef _LINUX_PID_H
#define _LINUX_PID_H
+#include <linux/file.h>
#include <linux/pid_types.h>
#include <linux/rculist.h>
#include <linux/rcupdate.h>
@@ -72,8 +73,47 @@ extern struct pid init_struct_pid;
struct file;
+
+/**
+ * __pidfd_get_pid() - Retrieve a pid associated with the specified pidfd.
+ *
+ * @pidfd: The pidfd whose pid we want, or the fd of a /proc/<pid> file if
+ * @alloc_proc is also set.
+ * @pin_pid: If set, then the reference counter of the returned pid is
+ * incremented. If not set, then @fd should be provided to pin the
+ * pidfd.
+ * @allow_proc: If set, then an fd of a /proc/<pid> file can be passed instead
+ * of a pidfd, and this will be used to determine the pid.
+ * @flags: Output variable, if non-NULL, then the file->f_flags of the
+ * pidfd will be set here.
+ * @fd: Output variable, if non-NULL, then the pidfd reference will
+ * remain elevated and the caller will need to decrement it
+ * themselves.
+ *
+ * Returns: If successful, the pid associated with the pidfd, otherwise an
+ * error.
+ */
+struct pid *__pidfd_get_pid(unsigned int pidfd, bool pin_pid,
+ bool allow_proc, unsigned int *flags,
+ struct fd *fd);
+
+static inline struct pid *pidfd_get_pid(unsigned int pidfd, unsigned int *flags)
+{
+ return __pidfd_get_pid(pidfd, /* pin_pid = */ true,
+ /* allow_proc = */ false,
+ flags, /* fd = */ NULL);
+}
+
+static inline struct pid *pidfd_to_pid_proc(unsigned int pidfd,
+ unsigned int *flags,
+ struct fd *fd)
+{
+ return __pidfd_get_pid(pidfd, /* pin_pid = */ false,
+ /* allow_proc = */ true,
+ flags, fd);
+}
+
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_prepare(struct pid *pid, unsigned int flags, struct file **ret);
void do_notify_pidfd(struct task_struct *task);
diff --git a/kernel/pid.c b/kernel/pid.c
index 2715afb77eab..25cc1c36a1b1 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -36,6 +36,7 @@
#include <linux/pid_namespace.h>
#include <linux/init_task.h>
#include <linux/syscalls.h>
+#include <linux/proc_fs.h>
#include <linux/proc_ns.h>
#include <linux/refcount.h>
#include <linux/anon_inodes.h>
@@ -534,22 +535,46 @@ struct pid *find_ge_pid(int nr, struct pid_namespace *ns)
}
EXPORT_SYMBOL_GPL(find_ge_pid);
-struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags)
+struct pid *__pidfd_get_pid(unsigned int pidfd, bool pin_pid,
+ bool allow_proc, unsigned int *flags,
+ struct fd *fd)
{
- struct fd f;
+ struct file *file;
struct pid *pid;
+ struct fd f = fdget(pidfd);
- f = fdget(fd);
- if (!fd_file(f))
+ file = fd_file(f);
+ if (!file)
return ERR_PTR(-EBADF);
- pid = pidfd_pid(fd_file(f));
- if (!IS_ERR(pid)) {
- get_pid(pid);
- *flags = fd_file(f)->f_flags;
+ pid = pidfd_pid(file);
+ /* If we allow opening a pidfd via /proc/<pid>, do so. */
+ if (IS_ERR(pid) && allow_proc)
+ pid = tgid_pidfd_to_pid(file);
+
+ if (IS_ERR(pid)) {
+ fdput(f);
+ return pid;
}
- fdput(f);
+ if (pin_pid)
+ get_pid(pid);
+ else
+ WARN_ON_ONCE(!fd); /* Nothing to keep pid/pidfd around? */
+
+ if (flags)
+ *flags = file->f_flags;
+
+ /*
+ * If the user provides an fd output then it will handle decrementing
+ * its reference counter.
+ */
+ if (fd)
+ *fd = f;
+ else
+ /* Otherwise we release it. */
+ fdput(f);
+
return pid;
}
@@ -747,23 +772,18 @@ SYSCALL_DEFINE3(pidfd_getfd, int, pidfd, int, fd,
unsigned int, flags)
{
struct pid *pid;
- struct fd f;
int ret;
/* flags is currently unused - make sure it's unset */
if (flags)
return -EINVAL;
- f = fdget(pidfd);
- if (!fd_file(f))
- return -EBADF;
-
- pid = pidfd_pid(fd_file(f));
+ pid = pidfd_get_pid(pidfd, NULL);
if (IS_ERR(pid))
- ret = PTR_ERR(pid);
- else
- ret = pidfd_getfd(pid, fd);
+ return PTR_ERR(pid);
- fdput(f);
+ ret = pidfd_getfd(pid, fd);
+
+ put_pid(pid);
return ret;
}
diff --git a/kernel/signal.c b/kernel/signal.c
index 4344860ffcac..868bfa674c62 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -3875,17 +3875,6 @@ static int copy_siginfo_from_user_any(kernel_siginfo_t *kinfo,
return copy_siginfo_from_user(kinfo, info);
}
-static struct pid *pidfd_to_pid(const struct file *file)
-{
- struct pid *pid;
-
- pid = pidfd_pid(file);
- if (!IS_ERR(pid))
- return pid;
-
- return tgid_pidfd_to_pid(file);
-}
-
#define PIDFD_SEND_SIGNAL_FLAGS \
(PIDFD_SIGNAL_THREAD | PIDFD_SIGNAL_THREAD_GROUP | \
PIDFD_SIGNAL_PROCESS_GROUP)
@@ -3908,10 +3897,11 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig,
siginfo_t __user *, info, unsigned int, flags)
{
int ret;
- struct fd f;
struct pid *pid;
kernel_siginfo_t kinfo;
enum pid_type type;
+ unsigned int f_flags;
+ struct fd f;
/* Enforce flags be set to 0 until we add an extension. */
if (flags & ~PIDFD_SEND_SIGNAL_FLAGS)
@@ -3921,12 +3911,8 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig,
if (hweight32(flags & PIDFD_SEND_SIGNAL_FLAGS) > 1)
return -EINVAL;
- f = fdget(pidfd);
- if (!fd_file(f))
- return -EBADF;
-
/* Is this a pidfd? */
- pid = pidfd_to_pid(fd_file(f));
+ pid = pidfd_to_pid_proc(pidfd, &f_flags, &f);
if (IS_ERR(pid)) {
ret = PTR_ERR(pid);
goto err;
@@ -3939,7 +3925,7 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig,
switch (flags) {
case 0:
/* Infer scope from the type of pidfd. */
- if (fd_file(f)->f_flags & PIDFD_THREAD)
+ if (f_flags & PIDFD_THREAD)
type = PIDTYPE_PID;
else
type = PIDTYPE_TGID;
--
2.46.2
