[PATCH v2] psi: allow unprivileged users with CAP_SYS_RESOURCE to write psi files

[Josh Hunt]

Currently only root can write files under /proc/pressure. Relax this to
allow tasks running as unprivileged users with CAP_SYS_RESOURCE to be
able to write to these files.

Signed-off-by: Josh Hunt <joh...@akamai.com>
Acked-by: Johannes Weiner <han...@cmpxchg.org>
---
 kernel/sched/psi.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index b1b00e9bd7ed..d1212f17a898 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -1061,19 +1061,27 @@ static int psi_cpu_show(struct seq_file *m, void *v)
        return psi_show(m, &psi_system, PSI_CPU);
 }
 
+static int psi_open(struct file *file, int (*psi_show)(struct seq_file *, void 
*))
+{
+       if (file->f_mode & FMODE_WRITE && !capable(CAP_SYS_RESOURCE))
+               return -EPERM;
+
+       return single_open(file, psi_show, NULL);
+}
+
 static int psi_io_open(struct inode *inode, struct file *file)
 {
-       return single_open(file, psi_io_show, NULL);
+       return psi_open(file, psi_io_show);
 }
 
 static int psi_memory_open(struct inode *inode, struct file *file)
 {
-       return single_open(file, psi_memory_show, NULL);
+       return psi_open(file, psi_memory_show);
 }
 
 static int psi_cpu_open(struct inode *inode, struct file *file)
 {
-       return single_open(file, psi_cpu_show, NULL);
+       return psi_open(file, psi_cpu_show);
 }
 
 struct psi_trigger *psi_trigger_create(struct psi_group *group,
@@ -1353,9 +1361,9 @@ static int __init psi_proc_init(void)
 {
        if (psi_enable) {
                proc_mkdir("pressure", NULL);
-               proc_create("pressure/io", 0, NULL, &psi_io_proc_ops);
-               proc_create("pressure/memory", 0, NULL, &psi_memory_proc_ops);
-               proc_create("pressure/cpu", 0, NULL, &psi_cpu_proc_ops);
+               proc_create("pressure/io", 0666, NULL, &psi_io_proc_ops);
+               proc_create("pressure/memory", 0666, NULL, 
&psi_memory_proc_ops);
+               proc_create("pressure/cpu", 0666, NULL, &psi_cpu_proc_ops);
        }
        return 0;
 }
-- 
2.17.1