[Devel] [PATCH RHEL8 COMMIT] fcntl: make F_GETOWN(EX) return 0 on dead owner task

[Konstantin Khorenko]

The commit is pushed to "branch-rh8-4.18.0-240.1.1.vz8.5.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh8-4.18.0-240.1.1.vz8.5.7
------>
commit ba4f56d1e73abcce28581be09d7cb0b3cb68861d
Author: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
Date:   Thu Mar 4 19:20:22 2021 +0300

    fcntl: make F_GETOWN(EX) return 0 on dead owner task
    
    Currently there is no way to differentiate file with alive owner from
    file with dead owner but pid of the owner reused. That's why criu can't
    actually know if it needs to restore file owner or not, because if it
    restores owner but actual owner was dead, this can introduce unexpected
    signals to the false-owner.
    
    Let's change the api, so that F_GETOWN(EX) returns 0 in case actual
    owner is dead already.
    
    https://jira.sw.ru/browse/PSBM-124623
    
    Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
---
 fs/fcntl.c | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/fs/fcntl.c b/fs/fcntl.c
index ff0cfd4d4c1e..e00cfb700cd8 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -178,11 +178,15 @@ void f_delown(struct file *filp)
 
 pid_t f_getown(struct file *filp)
 {
-	pid_t pid;
+	pid_t pid = 0;
 	read_lock(&filp->f_owner.lock);
-	pid = pid_vnr(filp->f_owner.pid);
-	if (filp->f_owner.pid_type == PIDTYPE_PGID)
-		pid = -pid;
+	rcu_read_lock();
+	if (pid_task(filp->f_owner.pid, filp->f_owner.pid_type)) {
+		pid = pid_vnr(filp->f_owner.pid);
+		if (filp->f_owner.pid_type == PIDTYPE_PGID)
+			pid = -pid;
+	}
+	rcu_read_unlock();
 	read_unlock(&filp->f_owner.lock);
 	return pid;
 }
@@ -230,11 +234,14 @@ static int f_setown_ex(struct file *filp, unsigned long arg)
 static int f_getown_ex(struct file *filp, unsigned long arg)
 {
 	struct f_owner_ex __user *owner_p = (void __user *)arg;
-	struct f_owner_ex owner;
+	struct f_owner_ex owner = {};
 	int ret = 0;
 
 	read_lock(&filp->f_owner.lock);
-	owner.pid = pid_vnr(filp->f_owner.pid);
+	rcu_read_lock();
+	if (pid_task(filp->f_owner.pid, filp->f_owner.pid_type))
+		owner.pid = pid_vnr(filp->f_owner.pid);
+	rcu_read_unlock();
 	switch (filp->f_owner.pid_type) {
 	case PIDTYPE_PID:
 		owner.type = F_OWNER_TID;