@@ -386,7 +386,7 @@ int ovl_xattr_set(struct dentry *dentry, struct inode *inode, const char *name,
}
int ovl_xattr_get(struct dentry *dentry, struct inode *inode, const char *name,
- void *value, size_t size)
+ void *value, size_t size, int flags)
{
ssize_t res;
const struct cred *old_cred;
@@ -394,7 +394,8 @@ int ovl_xattr_get(struct dentry *dentry, struct inode *inode, const char *name,
ovl_i_dentry_upper(inode) ?: ovl_dentry_lower(dentry);
old_cred = ovl_override_creds(dentry->d_sb);
- res = vfs_getxattr(&init_user_ns, realdentry, name, value, size);
+ res = __vfs_getxattr(&init_user_ns, realdentry, d_inode(realdentry),
+ name, value, size, flags);
revert_creds(old_cred);
return res;
}
@@ -187,7 +187,9 @@ static inline ssize_t ovl_do_getxattr(struct ovl_fs *ofs, struct dentry *dentry,
size_t size)
{
const char *name = ovl_xattr(ofs, ox);
- int err = vfs_getxattr(&init_user_ns, dentry, name, value, size);
+ struct inode *ip = d_inode(dentry);
+ int err = __vfs_getxattr(&init_user_ns, dentry, ip, name, value, size,
+ XATTR_NOSECURITY);
int len = (value && err > 0) ? err : 0;
pr_debug("getxattr(%pd2, \"%s\", \"%*pE\", %zu, 0) = %i\n",
@@ -496,7 +498,7 @@ int ovl_permission(struct user_namespace *mnt_userns, struct inode *inode,
int ovl_xattr_set(struct dentry *dentry, struct inode *inode, const char *name,
const void *value, size_t size, int flags);
int ovl_xattr_get(struct dentry *dentry, struct inode *inode, const char *name,
- void *value, size_t size);
+ void *value, size_t size, int flags);
ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size);
struct posix_acl *ovl_get_acl(struct inode *inode, int type, bool rcu);
int ovl_update_time(struct inode *inode, struct timespec64 *ts, int flags);
@@ -1006,7 +1006,7 @@ ovl_posix_acl_xattr_get(const struct xattr_handler *handler,
struct dentry *dentry, struct inode *inode,
const char *name, void *buffer, size_t size, int flags)
{
- return ovl_xattr_get(dentry, inode, handler->name, buffer, size);
+ return ovl_xattr_get(dentry, inode, handler->name, buffer, size, flags);
}
static int __maybe_unused
@@ -1087,7 +1087,7 @@ static int ovl_other_xattr_get(const struct xattr_handler *handler,
const char *name, void *buffer, size_t size,
int flags)
{
- return ovl_xattr_get(dentry, inode, name, buffer, size);
+ return ovl_xattr_get(dentry, inode, name, buffer, size, flags);
}
static int ovl_other_xattr_set(const struct xattr_handler *handler,
Because of the overlayfs getxattr recursion, the incoming inode fails to update the selinux sid resulting in avc denials being reported against a target context of u:object_r:unlabeled:s0. Solution is to respond to the XATTR_NOSECURITY flag in get xattr method that calls the __vfs_getxattr handler instead so that the context can be read in, rather than being denied with an -EACCES when vfs_getxattr handler is called. For the use case where access is to be blocked by the security layer. The path then would be security(dentry) -> __vfs_getxattr({dentry...XATTR_NOSECURITY}) -> handler->get({dentry...XATTR_NOSECURITY}) -> __vfs_getxattr({realdentry...XATTR_NOSECURITY}) -> lower_handler->get({realdentry...XATTR_NOSECURITY}) which would report back through the chain data and success as expected, the logging security layer at the top would have the data to determine the access permissions and report back to the logs and the caller that the target context was blocked. For selinux this would solve the cosmetic issue of the selinux log and allow audit2allow to correctly report the rule needed to address the access problem. Check impure, opaque, origin & meta xattr with no sepolicy audit (using __vfs_getxattr) since these operations are internal to overlayfs operations and do not disclose any data. This became an issue for credential override off since sys_admin would have been required by the caller; whereas would have been inherently present for the creator since it performed the mount. This is a change in operations since we do not check in the new ovl_do_getxattr function if the credential override is off or not. Reasoning is that the sepolicy check is unnecessary overhead, especially since the check can be expensive. Because for override credentials off, this affects _everyone_ that underneath performs private xattr calls without the appropriate sepolicy permissions and sys_admin capability. Providing blanket support for sys_admin would be bad for all possible callers. For the override credentials on, this will affect only the mounter, should it lack sepolicy permissions. Not considered a security problem since mounting by definition has sys_admin capabilities, but sepolicy contexts would still need to be crafted. It should be noted that there is precedence, __vfs_getxattr is used in other filesystems for their own internal trusted xattr management. Signed-off-by: Mark Salyzyn <salyzyn@android.com> Signed-off-by: David Anderson <dvander@google.com> Cc: linux-fsdevel@vger.kernel.org Cc: linux-unionfs@vger.kernel.org Cc: Stephen Smalley <sds@tycho.nsa.gov> Cc: linux-kernel@vger.kernel.org Cc: linux-security-module@vger.kernel.org Cc: kernel-team@android.com Cc: Miklos Szeredi <miklos@szeredi.hu> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Vivek Goyal <vgoyal@redhat.com> Cc: Eric W. Biederman <ebiederm@xmission.com> Cc: Amir Goldstein <amir73il@gmail.com> Cc: Stephen Smalley <sds@tycho.nsa.gov> Cc: linux-doc@vger.kernel.org Cc: selinux@vger.kernel.org Cc: paulmoore@microsoft.com Cc: Luca.Boccassi@microsoft.com v19 - rebase v18 - correct inode argument to __vfs_getxattr v17 - rebase and add inode argument to __vfs_getxattr v16 - rebase and merge internal getxattr operations patch v15 - revert to v13 because xattr_gs_args rejected. v14 - rebase to use xattr_gs_args. v13 - rebase to use __vfs_getxattr flags option. v12 - Added back to patch series as get xattr with flag option. v11 - Squashed out of patch series and replaced with per-thread flag solution. v10 - Added to patch series as __get xattr method. --- fs/overlayfs/inode.c | 5 +++-- fs/overlayfs/overlayfs.h | 6 ++++-- fs/overlayfs/super.c | 4 ++-- 3 files changed, 9 insertions(+), 6 deletions(-)