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LSM: add SafeSetID module that gates setid calls 

This change ensures that the set*uid family of syscalls in kernel/sys.c
(setreuid, setuid, setresuid, setfsuid) all call ns_capable_common with
the CAP_OPT_INSETID flag, so capability checks in the security_capable
hook can know whether they are being called from within a set*uid
syscall. This change is a no-op by itself, but is needed for the
proposed SafeSetID LSM.

Signed-off-by: Micah Morton <mortonm@chromium.org>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: James Morris <james.morris@microsoft.com>
This commit is contained in:
Micah Morton 2019-01-22 14:42:09 -08:00 committed by James Morris
parent 4b42564181
commit 40852275a9
3 changed files with 29 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
include/linux/capability.h
View File

@ -209,6 +209,7 @@ extern bool has_ns_capability_noaudit(struct task_struct *t,
extern bool capable(int cap);
extern bool ns_capable(struct user_namespace *ns, int cap);
extern bool ns_capable_noaudit(struct user_namespace *ns, int cap);
extern bool ns_capable_setid(struct user_namespace *ns, int cap);
#else
static inline bool has_capability(struct task_struct *t, int cap)
{
@ -240,6 +241,10 @@ static inline bool ns_capable_noaudit(struct user_namespace *ns, int cap)
{
return true;
}
static inline bool ns_capable_setid(struct user_namespace *ns, int cap)
{
return true;
}
#endif /* CONFIG_MULTIUSER */
extern bool privileged_wrt_inode_uidgid(struct user_namespace *ns, const struct inode *inode);
extern bool capable_wrt_inode_uidgid(const struct inode *inode, int cap);

19
kernel/capability.c
View File

@ -415,6 +415,25 @@ bool ns_capable_noaudit(struct user_namespace *ns, int cap)
}
EXPORT_SYMBOL(ns_capable_noaudit);
/**
* ns_capable_setid - Determine if the current task has a superior capability
* in effect, while signalling that this check is being done from within a
* setid syscall.
* @ns: The usernamespace we want the capability in
* @cap: The capability to be tested for
*
* Return true if the current task has the given superior capability currently
* available for use, false if not.
*
* This sets PF_SUPERPRIV on the task if the capability is available on the
* assumption that it's about to be used.
*/
bool ns_capable_setid(struct user_namespace *ns, int cap)
{
return ns_capable_common(ns, cap, CAP_OPT_INSETID);
}
EXPORT_SYMBOL(ns_capable_setid);
/**
* capable - Determine if the current task has a superior capability in effect
* @cap: The capability to be tested for

10
kernel/sys.c
View File

@ -516,7 +516,7 @@ long __sys_setreuid(uid_t ruid, uid_t euid)
new->uid = kruid;
if (!uid_eq(old->uid, kruid) &&
!uid_eq(old->euid, kruid) &&
!ns_capable(old->user_ns, CAP_SETUID))
!ns_capable_setid(old->user_ns, CAP_SETUID))
goto error;
}
@ -525,7 +525,7 @@ long __sys_setreuid(uid_t ruid, uid_t euid)
if (!uid_eq(old->uid, keuid) &&
!uid_eq(old->euid, keuid) &&
!uid_eq(old->suid, keuid) &&
!ns_capable(old->user_ns, CAP_SETUID))
!ns_capable_setid(old->user_ns, CAP_SETUID))
goto error;
}
@ -584,7 +584,7 @@ long __sys_setuid(uid_t uid)
old = current_cred();
retval = -EPERM;
if (ns_capable(old->user_ns, CAP_SETUID)) {
if (ns_capable_setid(old->user_ns, CAP_SETUID)) {
new->suid = new->uid = kuid;
if (!uid_eq(kuid, old->uid)) {
retval = set_user(new);
@ -646,7 +646,7 @@ long __sys_setresuid(uid_t ruid, uid_t euid, uid_t suid)
old = current_cred();
retval = -EPERM;
if (!ns_capable(old->user_ns, CAP_SETUID)) {
if (!ns_capable_setid(old->user_ns, CAP_SETUID)) {
if (ruid != (uid_t) -1 && !uid_eq(kruid, old->uid) &&
!uid_eq(kruid, old->euid) && !uid_eq(kruid, old->suid))
goto error;
@ -814,7 +814,7 @@ long __sys_setfsuid(uid_t uid)
if (uid_eq(kuid, old->uid) || uid_eq(kuid, old->euid) ||
uid_eq(kuid, old->suid) || uid_eq(kuid, old->fsuid) ||
ns_capable(old->user_ns, CAP_SETUID)) {
ns_capable_setid(old->user_ns, CAP_SETUID)) {
if (!uid_eq(kuid, old->fsuid)) {
new->fsuid = kuid;
if (security_task_fix_setuid(new, old, LSM_SETID_FS) == 0)