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authorJann Horn <jannh@google.com>2019-05-29 13:31:57 +0200
committerEric W. Biederman <ebiederm@xmission.com>2019-06-11 15:08:28 -0500
commitf6581f5b55141a95657ef5742cf6a6bfa20a109f (patch)
treea0ccd00874d67118ab48624da6ecb633da8c6536
parentf6e2aa91a46d2bc79fce9b93a988dbe7655c90c0 (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.c9
-rw-r--r--kernel/ptrace.c10
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) &&