diff options
| author | Jann Horn <jannh@google.com> | 2019-05-29 13:31:57 +0200 |
|---|---|---|
| committer | Eric W. Biederman <ebiederm@xmission.com> | 2019-06-11 15:08:28 -0500 |
| commit | f6581f5b55141a95657ef5742cf6a6bfa20a109f (patch) | |
| tree | a0ccd00874d67118ab48624da6ecb633da8c6536 | |
| parent | f6e2aa91a46d2bc79fce9b93a988dbe7655c90c0 (diff) | |
ptrace: restore smp_rmb() in __ptrace_may_access()
Restore the read memory barrier in __ptrace_may_access() that was deleted
a couple years ago. Also add comments on this barrier and the one it pairs
with to explain why they're there (as far as I understand).
Fixes: bfedb589252c ("mm: Add a user_ns owner to mm_struct and fix ptrace permission checks")
Cc: stable@vger.kernel.org
Acked-by: Kees Cook <keescook@chromium.org>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
| -rw-r--r-- | kernel/cred.c | 9 | ||||
| -rw-r--r-- | kernel/ptrace.c | 10 |
2 files changed, 19 insertions, 0 deletions
diff --git a/kernel/cred.c b/kernel/cred.c index 45d77284aed0..07e069d00696 100644 --- a/kernel/cred.c +++ b/kernel/cred.c @@ -450,6 +450,15 @@ int commit_creds(struct cred *new) if (task->mm) set_dumpable(task->mm, suid_dumpable); task->pdeath_signal = 0; + /* + * If a task drops privileges and becomes nondumpable, + * the dumpability change must become visible before + * the credential change; otherwise, a __ptrace_may_access() + * racing with this change may be able to attach to a task it + * shouldn't be able to attach to (as if the task had dropped + * privileges without becoming nondumpable). + * Pairs with a read barrier in __ptrace_may_access(). + */ smp_wmb(); } diff --git a/kernel/ptrace.c b/kernel/ptrace.c index 02c6528ead5c..c9b4646ad375 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -323,6 +323,16 @@ static int __ptrace_may_access(struct task_struct *task, unsigned int mode) return -EPERM; ok: rcu_read_unlock(); + /* + * If a task drops privileges and becomes nondumpable (through a syscall + * like setresuid()) while we are trying to access it, we must ensure + * that the dumpability is read after the credentials; otherwise, + * we may be able to attach to a task that we shouldn't be able to + * attach to (as if the task had dropped privileges without becoming + * nondumpable). + * Pairs with a write barrier in commit_creds(). + */ + smp_rmb(); mm = task->mm; if (mm && ((get_dumpable(mm) != SUID_DUMP_USER) && |