[PATCH RESEND v2 11/18] fs: Ensure the mounter of a filesystem is privileged towards its inodes

Seth Forshee
2016-01-04T18:03:50Z

The mounter of a filesystem should be privileged towards the
inodes of that filesystem. Extend the checks in
inode_owner_or_capable() and capable_wrt_inode_uidgid() to
permit access by users priviliged in the user namespace of the
inode's superblock.

Signed-off-by: Seth Forshee <seth.forshee-Z7WLFzj8eWMS+FvcfC7Uqw@public.gmane.org>
Acked-by: Serge Hallyn <serge.hallyn-Z7WLFzj8eWMS+FvcfC7Uqw@public.gmane.org>
---
fs/inode.c | 3 +++
kernel/capability.c | 13 +++++++++----
2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/fs/inode.c b/fs/inode.c
index 1be5f9003eb3..01c036fe1950 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1962,6 +1962,9 @@ bool inode_owner_or_capable(const struct inode *inode)
ns = current_user_ns();
if (ns_capable(ns, CAP_FOWNER) && kuid_has_mapping(ns, inode->i_uid))
return true;
+
+ if (ns_capable(inode->i_sb->s_user_ns, CAP_FOWNER))
+ return true;
return false;
}
EXPORT_SYMBOL(inode_owner_or_capable);
diff --git a/kernel/capability.c b/kernel/capability.c
index 45432b54d5c6..5137a38a5670 100644
--- a/kernel/capability.c
+++ b/kernel/capability.c
@@ -437,13 +437,18 @@ EXPORT_SYMBOL(file_ns_capable);
*
* Return true if the current task has the given capability targeted at
* its own user namespace and that the given inode's uid and gid are
- * mapped into the current user namespace.
+ * mapped into the current user namespace, or if the current task has
+ * the capability towards the user namespace of the inode's superblock.
*/
bool capable_wrt_inode_uidgid(const struct inode *inode, int cap)
{
- struct user_namespace *ns = current_user_ns();
+ struct user_namespace *ns;

- return ns_capable(ns, cap) && kuid_has_mapping(ns, inode->i_uid) &&
- kgid_has_mapping(ns, inode->i_gid);
+ ns = current_user_ns();
+ if (ns_capable(ns, cap) && kuid_has_mapping(ns, inode->i_uid) &&
+ kgid_has_mapping(ns, inode->i_gid))
+ return true;
+
+ return ns_capable(inode->i_sb->s_user_ns, cap);
}
EXPORT_SYMBOL(capable_wrt_inode_uidgid);
--
1.9.1

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