path: root/kernel/fork.c
diff options
authorEric W. Biederman <ebiederm@xmission.com>2016-10-13 21:23:16 -0500
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2017-01-06 10:40:13 +0100
commit694a95fa6dae4991f16cda333d897ea063021fed (patch)
treeac12876552e1b6585013a0e2932cf5da3c91def6 /kernel/fork.c
parentcfa2d65b2622d14b2f1368fbc9a6b4ab85141644 (diff)
mm: Add a user_ns owner to mm_struct and fix ptrace permission checks
commit bfedb589252c01fa505ac9f6f2a3d5d68d707ef4 upstream. 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 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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel/fork.c')
1 files changed, 6 insertions, 3 deletions
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)
-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;
@@ -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)
+ put_user_ns(mm->user_ns);
@@ -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);