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authorJann Horn <jannh@google.com>2019-05-29 13:31:57 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2019-06-22 08:18:22 +0200
commitd774bd27b4f5172f4506da96009c3de76e874362 (patch)
treebce8de0c5ceb531dd4ba2a3de9865801e4b4b2db /kernel/ptrace.c
parent5aff00ee839a7bb8eb86d4eddc1fdf7a40ca0622 (diff)
ptrace: restore smp_rmb() in __ptrace_may_access()
commit f6581f5b55141a95657ef5742cf6a6bfa20a109f upstream. 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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel/ptrace.c')
-rw-r--r--kernel/ptrace.c10
1 files changed, 10 insertions, 0 deletions
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index bb6db489833f..1aa33fe37aa8 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -292,6 +292,16 @@ 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) &&