[PATCH] fs/sync.c : Add CAP_SYS_ADMIN checking before sync

[Wuqixuan <wuqixuan@huawei.com>]

The process, supposed in one container, can't flush the metadata
and data of the all host's partitions without CAP_SYS_ADMIN
capability, like sys_mount is doing. The checking will prevent some
vicious programs impacting IO sequnces of those partitions,
particularly, the ones which can't be accessed in the container.

Signed-off-by: Last Wu <wuqixuan@huawei.com>
---
fs/sync.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/fs/sync.c b/fs/sync.c
index fbc98ee..9f07909 100644
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -103,6 +103,9 @@ SYSCALL_DEFINE0(sync)
{
int nowait = 0, wait = 1;

+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+
wakeup_flusher_threads(0, WB_REASON_SYNC);
iterate_supers(sync_inodes_one_sb, NULL);
iterate_supers(sync_fs_one_sb, &nowait);
--
1.9.1