On 7/30/2019 10:28 AM, Mark Salyzyn wrote: > Patch series: Please add linux-security-module@xxxxxxxxxxxxxxx to the CC for all changes affecting handling of security xattrs. > > overlayfs: check CAP_DAC_READ_SEARCH before issuing exportfs_decode_fh > Add flags option to get xattr method paired to __vfs_getxattr > overlayfs: handle XATTR_NOSECURITY flag for get xattr method > overlayfs: internal getxattr operations without sepolicy checking > overlayfs: override_creds=off option bypass creator_cred > > The first four patches address fundamental security issues that should > be solved regardless of the override_creds=off feature. > on them). > > The fifth adds the feature depends on these other fixes. > > By default, all access to the upper, lower and work directories is the > recorded mounter's MAC and DAC credentials. The incoming accesses are > checked against the caller's credentials. > > If the principles of least privilege are applied for sepolicy, the > mounter's credentials might not overlap the credentials of the caller's > when accessing the overlayfs filesystem. For example, a file that a > lower DAC privileged caller can execute, is MAC denied to the > generally higher DAC privileged mounter, to prevent an attack vector. > > We add the option to turn off override_creds in the mount options; all > subsequent operations after mount on the filesystem will be only the > caller's credentials. The module boolean parameter and mount option > override_creds is also added as a presence check for this "feature", > existence of /sys/module/overlay/parameters/overlay_creds > > Signed-off-by: Mark Salyzyn <salyzyn@xxxxxxxxxxx> > Cc: Miklos Szeredi <miklos@xxxxxxxxxx> > Cc: Jonathan Corbet <corbet@xxxxxxx> > Cc: Vivek Goyal <vgoyal@xxxxxxxxxx> > Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx> > Cc: Amir Goldstein <amir73il@xxxxxxxxx> > Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx> > Cc: Stephen Smalley <sds@xxxxxxxxxxxxx> > Cc: linux-unionfs@xxxxxxxxxxxxxxx > Cc: linux-doc@xxxxxxxxxxxxxxx > Cc: linux-kernel@xxxxxxxxxxxxxxx > > --- > v12: > - Restore squished out patch 2 and 3 in the series, > then change algorithm to add flags argument. > Per-thread flag is a large security surface. > > v11: > - Squish out v10 introduced patch 2 and 3 in the series, > then and use per-thread flag instead for nesting. > - Switch name to ovl_do_vds_getxattr for __vds_getxattr wrapper. > - Add sb argument to ovl_revert_creds to match future work. > > v10: > - Return NULL on CAP_DAC_READ_SEARCH > - Add __get xattr method to solve sepolicy logging issue > - Drop unnecessary sys_admin sepolicy checking for administrative > driver internal xattr functions. > > v6: > - Drop CONFIG_OVERLAY_FS_OVERRIDE_CREDS. > - Do better with the documentation, drop rationalizations. > - pr_warn message adjusted to report consequences. > > v5: > - beefed up the caveats in the Documentation > - Is dependent on > "overlayfs: check CAP_DAC_READ_SEARCH before issuing exportfs_decode_fh" > "overlayfs: check CAP_MKNOD before issuing vfs_whiteout" > - Added prwarn when override_creds=off > > v4: > - spelling and grammar errors in text > > v3: > - Change name from caller_credentials / creator_credentials to the > boolean override_creds. > - Changed from creator to mounter credentials. > - Updated and fortified the documentation. > - Added CONFIG_OVERLAY_FS_OVERRIDE_CREDS > > v2: > - Forward port changed attr to stat, resulting in a build error. > - altered commit message. >
