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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 /kernel/ptrace.c
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>
Diffstat (limited to 'kernel/ptrace.c')
-rw-r--r--kernel/ptrace.c26
1 files changed, 11 insertions, 15 deletions
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);