On Wed, Jun 15, 2016 at 4:01 PM, Vivek Goyal <vgoyal@xxxxxxxxxx> wrote:
> On Wed, Jun 15, 2016 at 03:30:02PM +0200, Miklos Szeredi wrote:
>> --- a/fs/overlayfs/dir.c
>> +++ b/fs/overlayfs/dir.c
>> @@ -405,12 +405,21 @@ static int ovl_create_or_link(struct den
>> err = ovl_create_upper(dentry, inode, &stat, link, hardlink);
>> } else {
>> const struct cred *old_cred;
>> + struct cred *override_cred;
>>
>> old_cred = ovl_override_creds(dentry->d_sb);
>>
>> - err = ovl_create_over_whiteout(dentry, inode, &stat, link,
>> - hardlink);
>> + err = -ENOMEM;
>> + override_cred = prepare_creds();
>> + if (override_cred) {
>> + override_cred->fsuid = old_cred->fsuid;
>> + override_cred->fsgid = old_cred->fsgid;
>
> Hi Miklos,
>
> I am wondering if we are switching to tasks's ->fsuid and ->fsgid too
> early. ovl_create_over_whiteout() calls ovl_lookup_temp(workdir) and
> IIUC, task might not have permission to do lookup in workdir.
>
> Should we switch to this override_cred, just before ovl_create_real()
> so that task ->fsuid and ->fsgid are used only for creation purposes
> only.
For lookup in workdir only CAP_DAC_OVERRIDE should matter, the actual
value of the fsuid and fsgid should be irrelevant (user, group and
others all have zero permission on workdir).
Thanks,
Miklos
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