exec: Ensure mm->user_ns contains the execed files

commit f84df2a6f268de584a201e8911384a2d244876e3 upstream.

When the user namespace support was merged the need to prevent
ptrace from revealing the contents of an unreadable executable
was overlooked.

Correct this oversight by ensuring that the executed file
or files are in mm->user_ns, by adjusting mm->user_ns.

Use the new function privileged_wrt_inode_uidgid to see if
the executable is a member of the user namespace, and as such
if having CAP_SYS_PTRACE in the user namespace should allow
tracing the executable.  If not update mm->user_ns to
the parent user namespace until an appropriate parent is found.

Reported-by: Jann Horn <jann@thejh.net>
Fixes: 9e4a36ece652 ("userns: Fail exec for suid and sgid binaries with ids outside our user namespace.")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/exec.c b/fs/exec.c
index 4e497b9ee71ee96d0647721e4649feff7adaf7c1..669c09bfdcadb3fbf683006e18208dd97d709538 100644 (file)
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1275,8 +1275,22 @@ EXPORT_SYMBOL(flush_old_exec);
 
 void would_dump(struct linux_binprm *bprm, struct file *file)
 {
-       if (inode_permission(file_inode(file), MAY_READ) < 0)
+       struct inode *inode = file_inode(file);
+       if (inode_permission(inode, MAY_READ) < 0) {
+               struct user_namespace *old, *user_ns;
                bprm->interp_flags |= BINPRM_FLAGS_ENFORCE_NONDUMP;
+
+               /* Ensure mm->user_ns contains the executable */
+               user_ns = old = bprm->mm->user_ns;
+               while ((user_ns != &init_user_ns) &&
+                      !privileged_wrt_inode_uidgid(user_ns, inode))
+                       user_ns = user_ns->parent;
+
+               if (old != user_ns) {
+                       bprm->mm->user_ns = get_user_ns(user_ns);
+                       put_user_ns(old);
+               }
+       }
 }
 EXPORT_SYMBOL(would_dump);
 
@@ -1306,7 +1320,6 @@ void setup_new_exec(struct linux_binprm * bprm)
            !gid_eq(bprm->cred->gid, current_egid())) {
                current->pdeath_signal = 0;
        } else {
-               would_dump(bprm, bprm->file);
                if (bprm->interp_flags & BINPRM_FLAGS_ENFORCE_NONDUMP)
                        set_dumpable(current->mm, suid_dumpable);
        }
@@ -1741,6 +1754,8 @@ static int do_execveat_common(int fd, struct filename *filename,
        if (retval < 0)
                goto out;
 
+       would_dump(bprm, bprm->file);
+
        retval = exec_binprm(bprm);
        if (retval < 0)
                goto out;

diff --git a/include/linux/capability.h b/include/linux/capability.h
index dbc21c719ce61b4aa45e90af3ec62ed9ced57b26..6ce3eefe2769517a618838bca7ee3ba28dc3d66c 100644 (file)
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -240,6 +240,7 @@ static inline bool ns_capable_noaudit(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);
 extern bool file_ns_capable(const struct file *file, struct user_namespace *ns, int cap);
 

diff --git a/kernel/capability.c b/kernel/capability.c
index 00411c82dac57c4cac0254c823f9adcb2a951549..c020c0047983b1a2ae10ed7bcf71b5c4cdf08424 100644 (file)
--- a/kernel/capability.c
+++ b/kernel/capability.c
@@ -456,6 +456,19 @@ bool file_ns_capable(const struct file *file, struct user_namespace *ns,
 }
 EXPORT_SYMBOL(file_ns_capable);
 
+/**
+ * privileged_wrt_inode_uidgid - Do capabilities in the namespace work over the inode?
+ * @ns: The user namespace in question
+ * @inode: The inode in question
+ *
+ * Return true if the inode uid and gid are within the namespace.
+ */
+bool privileged_wrt_inode_uidgid(struct user_namespace *ns, const struct inode *inode)
+{
+       return kuid_has_mapping(ns, inode->i_uid) &&
+               kgid_has_mapping(ns, inode->i_gid);
+}
+
 /**
  * capable_wrt_inode_uidgid - Check nsown_capable and uid and gid mapped
  * @inode: The inode in question
@@ -469,7 +482,6 @@ bool capable_wrt_inode_uidgid(const struct inode *inode, int cap)
 {
        struct user_namespace *ns = current_user_ns();
 
-       return ns_capable(ns, cap) && kuid_has_mapping(ns, inode->i_uid) &&
-               kgid_has_mapping(ns, inode->i_gid);
+       return ns_capable(ns, cap) && privileged_wrt_inode_uidgid(ns, inode);
 }
 EXPORT_SYMBOL(capable_wrt_inode_uidgid);