From 65026da59cda16baf6c3e98b74ec439f366e468f Mon Sep 17 00:00:00 2001 From: Jouni Roivas Date: Wed, 30 Sep 2020 19:42:42 +0300 Subject: [PATCH] cgroup: Zero sized write should be no-op 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 Signed-off-by: Tejun Heo --- kernel/cgroup/cgroup.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index 809b135..e41c218 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -3681,6 +3681,9 @@ 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 -- 2.7.4