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authorEric W. Biederman <ebiederm@xmission.com>2016-10-13 21:23:16 -0500
committerEric W. Biederman <ebiederm@xmission.com>2016-11-22 11:49:48 -0600
commitbfedb589252c01fa505ac9f6f2a3d5d68d707ef4 (patch)
treef4a3b443cc77423d0550c9a21d82175246a0f3d5
parent9c763584b7c8911106bb77af7e648bef09af9d80 (diff)
mm: Add a user_ns owner to mm_struct and fix ptrace permission checks
During exec dumpable is cleared if the file that is being executed is not readable by the user executing the file. A bug in ptrace_may_access allows reading the file if the executable happens to enter into a subordinate user namespace (aka clone(CLONE_NEWUSER), unshare(CLONE_NEWUSER), or setns(fd, CLONE_NEWUSER). This problem is fixed with only necessary userspace breakage by adding a user namespace owner to mm_struct, captured at the time of exec, so it is clear in which user namespace CAP_SYS_PTRACE must be present in to be able to safely give read permission to the executable. The function ptrace_may_access is modified to verify that the ptracer has CAP_SYS_ADMIN in task->mm->user_ns instead of task->cred->user_ns. This ensures that if the task changes it's cred into a subordinate user namespace it does not become ptraceable. The function ptrace_attach is modified to only set PT_PTRACE_CAP when CAP_SYS_PTRACE is held over task->mm->user_ns. The intent of PT_PTRACE_CAP is to be a flag to note that whatever permission changes the task might go through the tracer has sufficient permissions for it not to be an issue. task->cred->user_ns is always the same as or descendent of mm->user_ns. Which guarantees that having CAP_SYS_PTRACE over mm->user_ns is the worst case for the tasks credentials. To prevent regressions mm->dumpable and mm->user_ns are not considered when a task has no mm. As simply failing ptrace_may_attach causes regressions in privileged applications attempting to read things such as /proc/<pid>/stat Cc: stable@vger.kernel.org Acked-by: Kees Cook <keescook@chromium.org> Tested-by: Cyrill Gorcunov <gorcunov@openvz.org> Fixes: 8409cca70561 ("userns: allow ptrace from non-init user namespaces") Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
-rw-r--r--include/linux/mm_types.h1
-rw-r--r--kernel/fork.c9
-rw-r--r--kernel/ptrace.c26
-rw-r--r--mm/init-mm.c2
4 files changed, 20 insertions, 18 deletions
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 4a8acedf4b7d..08d947fc4c59 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -473,6 +473,7 @@ struct mm_struct {
*/
struct task_struct __rcu *owner;
#endif
+ struct user_namespace *user_ns;
/* store ref to file /proc/<pid>/exe symlink points to */
struct file __rcu *exe_file;
diff --git a/kernel/fork.c b/kernel/fork.c
index 997ac1d584f7..ba8a01564985 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -745,7 +745,8 @@ static void mm_init_owner(struct mm_struct *mm, struct task_struct *p)
#endif
}
-static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p)
+static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p,
+ struct user_namespace *user_ns)
{
mm->mmap = NULL;
mm->mm_rb = RB_ROOT;
@@ -785,6 +786,7 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p)
if (init_new_context(p, mm))
goto fail_nocontext;
+ mm->user_ns = get_user_ns(user_ns);
return mm;
fail_nocontext:
@@ -830,7 +832,7 @@ struct mm_struct *mm_alloc(void)
return NULL;
memset(mm, 0, sizeof(*mm));
- return mm_init(mm, current);
+ return mm_init(mm, current, current_user_ns());
}
/*
@@ -845,6 +847,7 @@ void __mmdrop(struct mm_struct *mm)
destroy_context(mm);
mmu_notifier_mm_destroy(mm);
check_mm(mm);
+ put_user_ns(mm->user_ns);
free_mm(mm);
}
EXPORT_SYMBOL_GPL(__mmdrop);
@@ -1126,7 +1129,7 @@ static struct mm_struct *dup_mm(struct task_struct *tsk)
memcpy(mm, oldmm, sizeof(*mm));
- if (!mm_init(mm, tsk))
+ if (!mm_init(mm, tsk, mm->user_ns))
goto fail_nomem;
err = dup_mmap(mm, oldmm);
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index e6474f7272ec..282821557183 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -220,7 +220,7 @@ static int ptrace_has_cap(struct user_namespace *ns, unsigned int mode)
static int __ptrace_may_access(struct task_struct *task, unsigned int mode)
{
const struct cred *cred = current_cred(), *tcred;
- int dumpable = 0;
+ struct mm_struct *mm;
kuid_t caller_uid;
kgid_t caller_gid;
@@ -271,16 +271,11 @@ static int __ptrace_may_access(struct task_struct *task, unsigned int mode)
return -EPERM;
ok:
rcu_read_unlock();
- smp_rmb();
- if (task->mm)
- dumpable = get_dumpable(task->mm);
- rcu_read_lock();
- if (dumpable != SUID_DUMP_USER &&
- !ptrace_has_cap(__task_cred(task)->user_ns, mode)) {
- rcu_read_unlock();
- return -EPERM;
- }
- rcu_read_unlock();
+ mm = task->mm;
+ if (mm &&
+ ((get_dumpable(mm) != SUID_DUMP_USER) &&
+ !ptrace_has_cap(mm->user_ns, mode)))
+ return -EPERM;
return security_ptrace_access_check(task, mode);
}
@@ -331,6 +326,11 @@ static int ptrace_attach(struct task_struct *task, long request,
task_lock(task);
retval = __ptrace_may_access(task, PTRACE_MODE_ATTACH_REALCREDS);
+ if (!retval) {
+ struct mm_struct *mm = task->mm;
+ if (mm && ns_capable(mm->user_ns, CAP_SYS_PTRACE))
+ flags |= PT_PTRACE_CAP;
+ }
task_unlock(task);
if (retval)
goto unlock_creds;
@@ -344,10 +344,6 @@ static int ptrace_attach(struct task_struct *task, long request,
if (seize)
flags |= PT_SEIZED;
- rcu_read_lock();
- if (ns_capable(__task_cred(task)->user_ns, CAP_SYS_PTRACE))
- flags |= PT_PTRACE_CAP;
- rcu_read_unlock();
task->ptrace = flags;
__ptrace_link(task, current);
diff --git a/mm/init-mm.c b/mm/init-mm.c
index a56a851908d2..975e49f00f34 100644
--- a/mm/init-mm.c
+++ b/mm/init-mm.c
@@ -6,6 +6,7 @@
#include <linux/cpumask.h>
#include <linux/atomic.h>
+#include <linux/user_namespace.h>
#include <asm/pgtable.h>
#include <asm/mmu.h>
@@ -21,5 +22,6 @@ struct mm_struct init_mm = {
.mmap_sem = __RWSEM_INITIALIZER(init_mm.mmap_sem),
.page_table_lock = __SPIN_LOCK_UNLOCKED(init_mm.page_table_lock),
.mmlist = LIST_HEAD_INIT(init_mm.mmlist),
+ .user_ns = &init_user_ns,
INIT_MM_CONTEXT(init_mm)
};