[PATCH 2/5] kernel/pid.c: implement checks on parameters passed to pidfd_create()

[Matthew Bobrowski <repnop@google.com>]

By adding the pidfd_create() declaration to linux/pid.h, it
effectively exposes this function to the rest of the kernel. As the
function currently stands, any part of the kernel could call
pidfd_create() and the pidfd creation would not be subject to the same
parameter constraints/checks as calling pidfd_open() would force upon
a caller. This could lead to unintended behavior and/or misuse of the
pidfd API.

To mitigate this, the pid_has_task() check is rolled up into
pidfd_create() and flags that are passed as parameter are checked for
validity.

Signed-off-by: Matthew Bobrowski <repnop@google.com>
---
 kernel/pid.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/kernel/pid.c b/kernel/pid.c
index d3cd95b8b080..1805cb3d74b7 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -559,6 +559,12 @@ int pidfd_create(struct pid *pid, unsigned int flags)
 {
 	int fd;
 
+	if (!pid || !pid_has_task(pid, PIDTYPE_TGID))
+		return -EINVAL;
+
+	if (flags & ~(O_NONBLOCK | O_CLOEXEC | O_RDWR))
+		return -EINVAL;
+
 	fd = anon_inode_getfd("[pidfd]", &pidfd_fops, get_pid(pid),
 			      flags | O_RDWR | O_CLOEXEC);
 	if (fd < 0)
@@ -598,10 +604,7 @@ SYSCALL_DEFINE2(pidfd_open, pid_t, pid, unsigned int, flags)
 	if (!p)
 		return -ESRCH;
 
-	if (pid_has_task(p, PIDTYPE_TGID))
-		fd = pidfd_create(p, flags);
-	else
-		fd = -EINVAL;
+	fd = pidfd_create(p, flags);
 
 	put_pid(p);
 	return fd;
-- 
2.31.1.751.gd2f1c929bd-goog

/M