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Yama: Check for pid death before checking ancestry

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commit 9474f4e7cd upstream.

It's possible that a pid has died before we take the rcu lock, in which
case we can't walk the ancestry list as it may be detached. Instead, check
for death first before doing the walk.

Reported-by: syzbot+a9ac39bf55329e206219@syzkaller.appspotmail.com
Fixes: 2d514487fa ("security: Yama LSM")
Cc: stable@vger.kernel.org
Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: James Morris <james.morris@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Kees Cook
2019-01-16 10:31:09 -08:00
committed by Greg Kroah-Hartman
parent bc42c4f338
commit e08323f75b
1 changed files with 3 additions and 1 deletions
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4
security/yama/yama_lsm.c
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@@ -288,7 +288,9 @@ static int yama_ptrace_access_check(struct task_struct *child,
break;
case YAMA_SCOPE_RELATIONAL:
rcu_read_lock();
if (!task_is_descendant(current, child) &&
if (!pid_alive(child))
rc = -EPERM;
if (!rc && !task_is_descendant(current, child) &&
!ptracer_exception_found(current, child) &&
!ns_capable(__task_cred(child)->user_ns, CAP_SYS_PTRACE))
rc = -EPERM;