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| author | Eric W. Biederman <ebiederm@xmission.com> | 2016-11-14 18:48:07 -0600 |
|---|---|---|
| committer | Eric W. Biederman <ebiederm@xmission.com> | 2016-11-22 11:49:49 -0600 |
| commit | 64b875f7ac8a5d60a4e191479299e931ee949b67 (patch) | |
| tree | 0c913f705ae947f5903ca0ff91ed633d1c2adc4a /kernel/ptrace.c | |
| parent | bfedb589252c01fa505ac9f6f2a3d5d68d707ef4 (diff) | |
| download | lwn-64b875f7ac8a5d60a4e191479299e931ee949b67.tar.gz lwn-64b875f7ac8a5d60a4e191479299e931ee949b67.zip | |
ptrace: Capture the ptracer's creds not PT_PTRACE_CAP
When the flag PT_PTRACE_CAP was added the PTRACE_TRACEME path was
overlooked. This can result in incorrect behavior when an application
like strace traces an exec of a setuid executable.
Further PT_PTRACE_CAP does not have enough information for making good
security decisions as it does not report which user namespace the
capability is in. This has already allowed one mistake through
insufficient granulariy.
I found this issue when I was testing another corner case of exec and
discovered that I could not get strace to set PT_PTRACE_CAP even when
running strace as root with a full set of caps.
This change fixes the above issue with strace allowing stracing as
root a setuid executable without disabling setuid. More fundamentaly
this change allows what is allowable at all times, by using the correct
information in it's decision.
Cc: stable@vger.kernel.org
Fixes: 4214e42f96d4 ("v2.4.9.11 -> v2.4.9.12")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Diffstat (limited to 'kernel/ptrace.c')
| -rw-r--r-- | kernel/ptrace.c | 12 |
1 files changed, 7 insertions, 5 deletions
diff --git a/kernel/ptrace.c b/kernel/ptrace.c index 282821557183..e82c15cadd6d 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -39,6 +39,9 @@ void __ptrace_link(struct task_struct *child, struct task_struct *new_parent) BUG_ON(!list_empty(&child->ptrace_entry)); list_add(&child->ptrace_entry, &new_parent->ptraced); child->parent = new_parent; + rcu_read_lock(); + child->ptracer_cred = get_cred(__task_cred(new_parent)); + rcu_read_unlock(); } /** @@ -71,12 +74,16 @@ void __ptrace_link(struct task_struct *child, struct task_struct *new_parent) */ void __ptrace_unlink(struct task_struct *child) { + const struct cred *old_cred; BUG_ON(!child->ptrace); clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE); child->parent = child->real_parent; list_del_init(&child->ptrace_entry); + old_cred = child->ptracer_cred; + child->ptracer_cred = NULL; + put_cred(old_cred); spin_lock(&child->sighand->siglock); child->ptrace = 0; @@ -326,11 +333,6 @@ static int ptrace_attach(struct task_struct *task, long request, task_lock(task); retval = __ptrace_may_access(task, PTRACE_MODE_ATTACH_REALCREDS); - if (!retval) { - struct mm_struct *mm = task->mm; - if (mm && ns_capable(mm->user_ns, CAP_SYS_PTRACE)) - flags |= PT_PTRACE_CAP; - } task_unlock(task); if (retval) goto unlock_creds; |