[PATCH 1/1] cgroup: limit cgroup psi file writes to processes with CAP_SYS_RESOURCE

[Suren Baghdasaryan <surenb@google.com>]

Currently /proc/pressure/* files can be written only by processes with
CAP_SYS_RESOURCE capability to prevent any unauthorized user from
creating psi triggers. However no such limitation is required for
per-cgroup pressure files. Fix this inconsistency by requiring the same
capability for writing per-cgroup psi files.

Fixes: 6db12ee0456d ("psi: allow unprivileged users with CAP_SYS_RESOURCE to write psi files")
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 kernel/cgroup/cgroup.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 935e8121b21e..b600a6baaeca 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -3867,6 +3867,12 @@ static __poll_t cgroup_pressure_poll(struct kernfs_open_file *of,
 	return psi_trigger_poll(&ctx->psi.trigger, of->file, pt);
 }
 
+static int cgroup_pressure_open(struct kernfs_open_file *of)
+{
+	return (of->file->f_mode & FMODE_WRITE && !capable(CAP_SYS_RESOURCE)) ?
+		-EPERM : 0;
+}
+
 static void cgroup_pressure_release(struct kernfs_open_file *of)
 {
 	struct cgroup_file_ctx *ctx = of->priv;
@@ -5266,6 +5272,7 @@ static struct cftype cgroup_psi_files[] = {
 	{
 		.name = "io.pressure",
 		.file_offset = offsetof(struct cgroup, psi_files[PSI_IO]),
+		.open = cgroup_pressure_open,
 		.seq_show = cgroup_io_pressure_show,
 		.write = cgroup_io_pressure_write,
 		.poll = cgroup_pressure_poll,
@@ -5274,6 +5281,7 @@ static struct cftype cgroup_psi_files[] = {
 	{
 		.name = "memory.pressure",
 		.file_offset = offsetof(struct cgroup, psi_files[PSI_MEM]),
+		.open = cgroup_pressure_open,
 		.seq_show = cgroup_memory_pressure_show,
 		.write = cgroup_memory_pressure_write,
 		.poll = cgroup_pressure_poll,
@@ -5282,6 +5290,7 @@ static struct cftype cgroup_psi_files[] = {
 	{
 		.name = "cpu.pressure",
 		.file_offset = offsetof(struct cgroup, psi_files[PSI_CPU]),
+		.open = cgroup_pressure_open,
 		.seq_show = cgroup_cpu_pressure_show,
 		.write = cgroup_cpu_pressure_write,
 		.poll = cgroup_pressure_poll,
@@ -5291,6 +5300,7 @@ static struct cftype cgroup_psi_files[] = {
 	{
 		.name = "irq.pressure",
 		.file_offset = offsetof(struct cgroup, psi_files[PSI_IRQ]),
+		.open = cgroup_pressure_open,
 		.seq_show = cgroup_irq_pressure_show,
 		.write = cgroup_irq_pressure_write,
 		.poll = cgroup_pressure_poll,
-- 
2.39.2.722.g9855ee24e9-goog