Messages in this thread | | | Date | Thu, 16 Apr 2015 21:31:21 +0200 | Subject | Re: [PATCH] fs/sync.c : Add CAP_SYS_ADMIN checking before sync | From | Richard Weinberger <> |
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On Thu, Apr 16, 2015 at 5:08 PM, Azat Khuzhin <a3at.mail@gmail.com> wrote: > On Thu, Apr 16, 2015 at 07:43:34PM +0800, Wuqixuan wrote: >> 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; > > So after this patch I can't call sync as a regular user? (even without > containers). > But nothing in sync(2) says about special permissions for this.
Yeah, this solution will break userspace. A much more generic solution would be to wait for cgroup aware writeback[1]. As temporary hack you can check whether the calling process is in the initial pid namesapce to detect a container calling sync(2)...
[1] https://lwn.net/Articles/628631/
-- Thanks, //richard
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