On Sat, Jul 22, 2017 at 11:30 AM, Amir Goldstein <amir73il@xxxxxxxxx> wrote: > Bumped into this patch (Now upstream commit 51f8f3c4e225) and realized > it is missing cc: stable # v4.8 > > At least this docker PR suggests that regression introduced in v4.8 will not be > appreciated down the road: > https://github.com/moby/moby/issues/29364 Greg, Can you please queue 51f8f3c4e225 ("ovl: drop CAP_SYS_RESOURCE from saved mounter's credentials") for 4.9.y? Thanks, Miklos > > > On Tue, Jan 10, 2017 at 9:17 PM, Vivek Goyal <vgoyal@xxxxxxxxxx> wrote: >> On Tue, Jan 10, 2017 at 09:30:21PM +0300, Konstantin Khlebnikov wrote: >>> If overlay was mounted by root then quota set for upper layer does not work >>> because overlay now always use mounter's credentials for operations. >>> Also overlay might deplete reserved space and inodes in ext4. >>> >>> This patch drops capability SYS_RESOURCE from saved credentials. >>> This affects creation new files, whiteouts, and copy-up operations. >>> >> >> I am not an expert in this area, but I thought previous patch was >> better. I am not sure why overlay internal operations should be >> done without CAP_SYS_RESOURCES when caller has CAP_SYS_RESOURCES. That >> might be counter-intuitive. >> >> If some task is allowed to bypass quota limitations on a file system >> then same should be true when task is working on overlay. >> >> Similary if a task is allowed to use reserved space on filesystem, then same >> task should be allowed to use reserved space on underlying filesystem >> when doing overlay. It should not be overlay's job to prevent that? >> >> May be it is just me.... >> > > Vivek, > > Since your question was not answered in this thread, IMO, your concern > is just, but in practice I think that: > 1. It's going to be harder to implement for every operation to combine the > mounter's creds with the process capabilities... weird > 2. The use case of ext4 reserved blocks is to allow sys admin some slack > for disk allocations that are needed in order to free up disk space or for > other critical tasks to prevent the system from hanging. It doesn't sound > like this use case fits an overlayfs mount that well. > 3. FYI, xfs project quota (which as you know can be applied to docker > overlayfs container) does not check CAP_SYS_RESOURCES at all. > and if and when ext4 project quotas can also be applied to docker > overlayfs container, I am sure that containers admin will not appreciate > a container exceeding its quota, even if that was a privileged process > writing to that container > > So IMO that fix as it is is good for all practical purpose. > > Cheers, > Amir. > >> >> >>> Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx> >>> Fixes: 1175b6b8d963 ("ovl: do operations on underlying file system in mounter's context") >>> Cc: Vivek Goyal <vgoyal@xxxxxxxxxx> >>> Cc: Miklos Szeredi <mszeredi@xxxxxxxxxx> >>> --- >>> fs/overlayfs/super.c | 9 +++++++-- >>> 1 file changed, 7 insertions(+), 2 deletions(-) >>> >>> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c >>> index 20f48abbb82f..8dba982e1af5 100644 >>> --- a/fs/overlayfs/super.c >>> +++ b/fs/overlayfs/super.c >>> @@ -701,6 +701,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent) >>> unsigned int stacklen = 0; >>> unsigned int i; >>> bool remote = false; >>> + struct cred *cred; >>> int err; >>> >>> err = -ENOMEM; >>> @@ -870,10 +871,14 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent) >>> else >>> sb->s_d_op = &ovl_dentry_operations; >>> >>> - ufs->creator_cred = prepare_creds(); >>> - if (!ufs->creator_cred) >>> + cred = prepare_creds(); >>> + if (!cred) >>> goto out_put_lower_mnt; >>> >>> + /* Never override disk quota limits or use reserved space */ >>> + cap_lower(cred->cap_effective, CAP_SYS_RESOURCE); >>> + ufs->creator_cred = cred; >>> + >>> err = -ENOMEM; >>> oe = ovl_alloc_entry(numlower); >>> if (!oe)
