Do not report failure on zero sized writes, and handle them as no-op.
There's issues for example in case of writev() when there's iovec
containing zero buffer as a first one. It's expected writev() on below
example to successfully perform the write to specified writable cgroup
file expecting integer value, and to return 2. For now it's returning
value -1, and skipping the write:
int writetest(int fd) {
const char *buf1 = "";
const char *buf2 = "1\n";
struct iovec iov[2] = {
{ .iov_base = (void*)buf1, .iov_len = 0 },
{ .iov_base = (void*)buf2, .iov_len = 2 }
};
return writev(fd, iov, 2);
}
This patch fixes the issue by checking if there's nothing to write,
and handling the write as no-op by just returning 0.
Signed-off-by: Jouni Roivas <jouni.roivas@xxxxxxxxxx>
---
kernel/cgroup/cgroup.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index dd247747ec14..c26ba71c3d93 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -3682,6 +3682,9 @@ static ssize_t cgroup_file_write(struct kernfs_open_file *of, char *buf,
struct cgroup_subsys_state *css;
int ret;
+ if (!nbytes)
+ return 0;
+
/*
* If namespaces are delegation boundaries, disallow writes to
* files in an non-init namespace root from inside the namespace
--
2.25.1
