[PATCH] selinux: check CAP_SETFCAP for a particular inode & mapped user

From: Lubomir Rintel
Date: Thu Oct 05 2017 - 02:16:32 EST


This allows setting "security.capability" xattr by a user that has
CAP_SETFCAP in an userns with SELinux. Namespaced capabilities are
supported, as of commit 8db6c34f1dbc ("Introduce v3 namespaced file
capabilities").

Signed-off-by: Lubomir Rintel <lkundrak@xxxxx>
---
A casual warning: Please not assume I know what I'm really doing. I can now
install iputils and /bin/ping in a LXC container, which is great, but I
typically wouldn't be allowed anywhere near anything security related.

Thank you!

security/selinux/hooks.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index f5d304736852..7bc5f4ffb4e0 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3127,11 +3127,12 @@ static int selinux_inode_getattr(const struct path *path)
static int selinux_inode_setotherxattr(struct dentry *dentry, const char *name)
{
const struct cred *cred = current_cred();
+ struct inode *inode = d_backing_inode(dentry);

if (!strncmp(name, XATTR_SECURITY_PREFIX,
sizeof XATTR_SECURITY_PREFIX - 1)) {
if (!strcmp(name, XATTR_NAME_CAPS)) {
- if (!capable(CAP_SETFCAP))
+ if (!capable_wrt_inode_uidgid(inode, CAP_SETFCAP))
return -EPERM;
} else if (!capable(CAP_SYS_ADMIN)) {
/* A different attribute in the security namespace.
--
2.13.6