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>
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@ -209,6 +209,7 @@ extern bool has_ns_capability_noaudit(struct task_struct *t,
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extern bool capable(int cap);
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extern bool ns_capable(struct user_namespace *ns, int cap);
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extern bool ns_capable_noaudit(struct user_namespace *ns, int cap);
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extern bool ns_capable_setid(struct user_namespace *ns, int cap);
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#else
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static inline bool has_capability(struct task_struct *t, int cap)
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{
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@ -240,6 +241,10 @@ static inline bool ns_capable_noaudit(struct user_namespace *ns, int cap)
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{
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return true;
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}
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static inline bool ns_capable_setid(struct user_namespace *ns, int cap)
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{
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return true;
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}
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#endif /* CONFIG_MULTIUSER */
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extern bool privileged_wrt_inode_uidgid(struct user_namespace *ns, const struct inode *inode);
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extern bool capable_wrt_inode_uidgid(const struct inode *inode, int cap);
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@ -415,6 +415,25 @@ bool ns_capable_noaudit(struct user_namespace *ns, int cap)
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}
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EXPORT_SYMBOL(ns_capable_noaudit);
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/**
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* ns_capable_setid - Determine if the current task has a superior capability
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* in effect, while signalling that this check is being done from within a
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* setid syscall.
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* @ns: The usernamespace we want the capability in
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* @cap: The capability to be tested for
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*
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* Return true if the current task has the given superior capability currently
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* available for use, false if not.
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*
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* This sets PF_SUPERPRIV on the task if the capability is available on the
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* assumption that it's about to be used.
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*/
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bool ns_capable_setid(struct user_namespace *ns, int cap)
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{
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return ns_capable_common(ns, cap, CAP_OPT_INSETID);
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}
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EXPORT_SYMBOL(ns_capable_setid);
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/**
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* capable - Determine if the current task has a superior capability in effect
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* @cap: The capability to be tested for
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10
kernel/sys.c
10
kernel/sys.c
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@ -516,7 +516,7 @@ long __sys_setreuid(uid_t ruid, uid_t euid)
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new->uid = kruid;
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if (!uid_eq(old->uid, kruid) &&
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!uid_eq(old->euid, kruid) &&
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!ns_capable(old->user_ns, CAP_SETUID))
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!ns_capable_setid(old->user_ns, CAP_SETUID))
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goto error;
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}
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@ -525,7 +525,7 @@ long __sys_setreuid(uid_t ruid, uid_t euid)
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if (!uid_eq(old->uid, keuid) &&
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!uid_eq(old->euid, keuid) &&
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!uid_eq(old->suid, keuid) &&
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!ns_capable(old->user_ns, CAP_SETUID))
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!ns_capable_setid(old->user_ns, CAP_SETUID))
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goto error;
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}
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@ -584,7 +584,7 @@ long __sys_setuid(uid_t uid)
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old = current_cred();
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retval = -EPERM;
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if (ns_capable(old->user_ns, CAP_SETUID)) {
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if (ns_capable_setid(old->user_ns, CAP_SETUID)) {
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new->suid = new->uid = kuid;
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if (!uid_eq(kuid, old->uid)) {
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retval = set_user(new);
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@ -646,7 +646,7 @@ long __sys_setresuid(uid_t ruid, uid_t euid, uid_t suid)
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old = current_cred();
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retval = -EPERM;
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if (!ns_capable(old->user_ns, CAP_SETUID)) {
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if (!ns_capable_setid(old->user_ns, CAP_SETUID)) {
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if (ruid != (uid_t) -1 && !uid_eq(kruid, old->uid) &&
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!uid_eq(kruid, old->euid) && !uid_eq(kruid, old->suid))
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goto error;
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@ -814,7 +814,7 @@ long __sys_setfsuid(uid_t uid)
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if (uid_eq(kuid, old->uid) || uid_eq(kuid, old->euid) ||
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uid_eq(kuid, old->suid) || uid_eq(kuid, old->fsuid) ||
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ns_capable(old->user_ns, CAP_SETUID)) {
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ns_capable_setid(old->user_ns, CAP_SETUID)) {
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if (!uid_eq(kuid, old->fsuid)) {
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new->fsuid = kuid;
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if (security_task_fix_setuid(new, old, LSM_SETID_FS) == 0)
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