diff options
author | Jann Horn <jannh@google.com> | 2019-07-04 17:32:23 +0200 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2019-07-10 09:55:45 +0200 |
commit | d8b99303da935228a33fa7656a964adfb33e271b (patch) | |
tree | 746dad7007215f660ed19fa1adcb4a6392a3ca5b /kernel | |
parent | e7816df0494bf4c49b6c7d20dbfec4e1a1a016c2 (diff) |
ptrace: Fix ->ptracer_cred handling for PTRACE_TRACEME
commit 6994eefb0053799d2e07cd140df6c2ea106c41ee upstream.
Fix two issues:
When called for PTRACE_TRACEME, ptrace_link() would obtain an RCU
reference to the parent's objective credentials, then give that pointer
to get_cred(). However, the object lifetime rules for things like
struct cred do not permit unconditionally turning an RCU reference into
a stable reference.
PTRACE_TRACEME records the parent's credentials as if the parent was
acting as the subject, but that's not the case. If a malicious
unprivileged child uses PTRACE_TRACEME and the parent is privileged, and
at a later point, the parent process becomes attacker-controlled
(because it drops privileges and calls execve()), the attacker ends up
with control over two processes with a privileged ptrace relationship,
which can be abused to ptrace a suid binary and obtain root privileges.
Fix both of these by always recording the credentials of the process
that is requesting the creation of the ptrace relationship:
current_cred() can't change under us, and current is the proper subject
for access control.
This change is theoretically userspace-visible, but I am not aware of
any code that it will actually break.
Fixes: 64b875f7ac8a ("ptrace: Capture the ptracer's creds not PT_PTRACE_CAP")
Signed-off-by: Jann Horn <jannh@google.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel')
-rw-r--r-- | kernel/ptrace.c | 4 |
1 files changed, 1 insertions, 3 deletions
diff --git a/kernel/ptrace.c b/kernel/ptrace.c index f447f1e36185..ea3370e205fb 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -74,9 +74,7 @@ void __ptrace_link(struct task_struct *child, struct task_struct *new_parent, */ static void ptrace_link(struct task_struct *child, struct task_struct *new_parent) { - rcu_read_lock(); - __ptrace_link(child, new_parent, __task_cred(new_parent)); - rcu_read_unlock(); + __ptrace_link(child, new_parent, current_cred()); } /** |