[PATCH] UNTESTED, SKETCH, DRAFT

[Christian Brauner]

Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
---
 fs/pidfs.c            | 42 +++++++++++++++++++++++++++++++++++++
 include/linux/pidfs.h | 29 +++++++++++++++++++++++++
 kernel/signal.c       | 49 ++++++++++++-------------------------------
 3 files changed, 84 insertions(+), 36 deletions(-)

diff --git a/fs/pidfs.c b/fs/pidfs.c
index 80675b6bf884..de7e9e6bbd22 100644
--- a/fs/pidfs.c
+++ b/fs/pidfs.c
@@ -22,6 +22,48 @@
 #include "internal.h"
 #include "mount.h"
 
+struct pid_fd pidfd_get(int fd)
+{
+	struct fd f;
+	struct pid *pid;
+
+	/* handle PIDFD_SELF_* cases */
+	if (fd < 0) {
+		if (fd == PIDFD_SELF_THREAD)
+			return (struct pid_fd){ .fd = EMPTY_FD, .pid = get_task_pid(current, PIDTYPE_PID) };
+		if (fd == PIDFD_SELF_THREAD_GROUP)
+			return (struct pid_fd){ .fd = EMPTY_FD, .pid = get_task_pid(current, PIDTYPE_TGID) };
+		return (struct pid_fd){ .fd = EMPTY_FD, .pid = ERR_PTR(-EBADF) };
+	}
+
+	/* handle the regular case */
+	f = fdget(fd);
+	if (!fd_file(f))
+		return (struct pid_fd){ .fd = EMPTY_FD, .pid = ERR_PTR(-EBADF) };
+
+	pid = pidfd_pid(fd_file(f));
+	if (IS_ERR(pid)) {
+		fdput(f);
+		return (struct pid_fd) { .fd = EMPTY_FD, .pid = pid };
+	}
+
+	return (struct pid_fd) { .fd = f, pid = pid } ;
+}
+
+void pidfd_put(struct pid_fd fd)
+{
+	/*
+	 * Handle PIDFD_SELF_* where the struct pid hasn't been attached
+	 * to a file.
+	 */
+	if (fd_empty(fd.fd) && pidfd_valid(fd))
+		put_pid(fd.pid);
+
+	/* Can call unconditionally safely. */
+	fdput(fd.fd);
+
+}
+
 #ifdef CONFIG_PROC_FS
 /**
  * pidfd_show_fdinfo - print information about a pidfd
diff --git a/include/linux/pidfs.h b/include/linux/pidfs.h
index 75bdf9807802..ad86b69ee1ea 100644
--- a/include/linux/pidfs.h
+++ b/include/linux/pidfs.h
@@ -2,6 +2,35 @@
 #ifndef _LINUX_PID_FS_H
 #define _LINUX_PID_FS_H
 
+#include <linux/file.h>
+#include <linux/cleanup.h>
+
+#define PIDFD_SELF           PIDFD_SELF_THREAD
+#define PIDFD_SELF_PROCESS   PIDFD_SELF_THREAD_GROUP
+
+#define PIDFD_SELF_THREAD		-10000 /* Current thread. */
+#define PIDFD_SELF_THREAD_GROUP		-20000 /* Current thread group leader. */
+
+struct pid_fd {
+	struct fd fd;
+	struct pid *pid;
+};
+
+static inline struct pid *pid_fd_pid(struct pid_fd pfd)
+{
+	return pfd.pid;
+}
+
+static inline bool pidfd_valid(struct pid_fd pfd)
+{
+	return !IS_ERR(pid_fd_pid(pfd));
+}
+
+struct pid_fd pidfd_get(int fd);
+void pidfd_put(struct pid_fd fd);
+
+DEFINE_CLASS(pid_fd, struct pid_fd, pidfd_put(_T), pidfd_get(fd), int fd)
+
 struct file *pidfs_alloc_file(struct pid *pid, unsigned int flags);
 void __init pidfs_init(void);
 
diff --git a/kernel/signal.c b/kernel/signal.c
index 4344860ffcac..16b10e726038 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -47,6 +47,7 @@
 #include <linux/cgroup.h>
 #include <linux/audit.h>
 #include <linux/sysctl.h>
+#include <linux/pidfs.h>
 #include <uapi/linux/pidfd.h>
 
 #define CREATE_TRACE_POINTS
@@ -3875,17 +3876,6 @@ 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)
@@ -3908,7 +3898,6 @@ 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;
@@ -3921,25 +3910,18 @@ 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));
-	if (IS_ERR(pid)) {
-		ret = PTR_ERR(pid);
-		goto err;
-	}
+	CLASS(pid_fd, pid_fd)(pidfd);
+	if (!pidfd_valid(pid_fd))
+		return PTR_ERR(pid_fd_pid(pid_fd));
 
-	ret = -EINVAL;
+	pid = pid_fd_pid(pid_fd);
 	if (!access_pidfd_pidns(pid))
-		goto err;
+		return -EINVAL;
 
 	switch (flags) {
 	case 0:
 		/* Infer scope from the type of pidfd. */
-		if (fd_file(f)->f_flags & PIDFD_THREAD)
+		if (pidfd > 0 && fd_file(pid_fd.fd)->f_flags & PIDFD_THREAD)
 			type = PIDTYPE_PID;
 		else
 			type = PIDTYPE_TGID;
@@ -3958,28 +3940,23 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig,
 	if (info) {
 		ret = copy_siginfo_from_user_any(&kinfo, info);
 		if (unlikely(ret))
-			goto err;
+			return ret;
 
-		ret = -EINVAL;
 		if (unlikely(sig != kinfo.si_signo))
-			goto err;
+			return -EINVAL;
 
 		/* Only allow sending arbitrary signals to yourself. */
-		ret = -EPERM;
 		if ((task_pid(current) != pid || type > PIDTYPE_TGID) &&
 		    (kinfo.si_code >= 0 || kinfo.si_code == SI_TKILL))
-			goto err;
+			return -EPERM;
 	} else {
 		prepare_kill_siginfo(sig, &kinfo, type);
 	}
 
 	if (type == PIDTYPE_PGID)
-		ret = kill_pgrp_info(sig, &kinfo, pid);
-	else
-		ret = kill_pid_info_type(sig, &kinfo, pid, type);
-err:
-	fdput(f);
-	return ret;
+		return kill_pgrp_info(sig, &kinfo, pid);
+
+	return kill_pid_info_type(sig, &kinfo, pid, type);
 }
 
 static int
-- 
2.45.2


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