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authorEric W. Biederman <ebiederm@xmission.com>2017-05-22 15:40:12 -0500
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2017-06-14 15:05:54 +0200
commit7c24a70c70b7a1ff71cbf410358c6c45daccdc74 (patch)
tree2a0dce5b3bada49e206268399d7ce87e2ee4453e
parent3802abc6e0dfa892d7205fac199b0e2d68cec056 (diff)
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ptrace: Properly initialize ptracer_cred on fork
commit c70d9d809fdeecedb96972457ee45c49a232d97f upstream. When I introduced ptracer_cred I failed to consider the weirdness of fork where the task_struct copies the old value by default. This winds up leaving ptracer_cred set even when a process forks and the child process does not wind up being ptraced. Because ptracer_cred is not set on non-ptraced processes whose parents were ptraced this has broken the ability of the enlightenment window manager to start setuid children. Fix this by properly initializing ptracer_cred in ptrace_init_task This must be done with a little bit of care to preserve the current value of ptracer_cred when ptrace carries through fork. Re-reading the ptracer_cred from the ptracing process at this point is inconsistent with how PT_PTRACE_CAP has been maintained all of these years. Tested-by: Takashi Iwai <tiwai@suse.de> Fixes: 64b875f7ac8a ("ptrace: Capture the ptracer's creds not PT_PTRACE_CAP") Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--include/linux/ptrace.h7
-rw-r--r--kernel/ptrace.c20
2 files changed, 18 insertions, 9 deletions
diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
index e0e539321ab9..d53a23100401 100644
--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -53,7 +53,8 @@ extern int ptrace_request(struct task_struct *child, long request,
unsigned long addr, unsigned long data);
extern void ptrace_notify(int exit_code);
extern void __ptrace_link(struct task_struct *child,
- struct task_struct *new_parent);
+ struct task_struct *new_parent,
+ const struct cred *ptracer_cred);
extern void __ptrace_unlink(struct task_struct *child);
extern void exit_ptrace(struct task_struct *tracer, struct list_head *dead);
#define PTRACE_MODE_READ 0x01
@@ -205,7 +206,7 @@ static inline void ptrace_init_task(struct task_struct *child, bool ptrace)
if (unlikely(ptrace) && current->ptrace) {
child->ptrace = current->ptrace;
- __ptrace_link(child, current->parent);
+ __ptrace_link(child, current->parent, current->ptracer_cred);
if (child->ptrace & PT_SEIZED)
task_set_jobctl_pending(child, JOBCTL_TRAP_STOP);
@@ -214,6 +215,8 @@ static inline void ptrace_init_task(struct task_struct *child, bool ptrace)
set_tsk_thread_flag(child, TIF_SIGPENDING);
}
+ else
+ child->ptracer_cred = NULL;
}
/**
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index a5caecef88be..f39a7be98fc1 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -57,19 +57,25 @@ int ptrace_access_vm(struct task_struct *tsk, unsigned long addr,
}
+void __ptrace_link(struct task_struct *child, struct task_struct *new_parent,
+ const struct cred *ptracer_cred)
+{
+ BUG_ON(!list_empty(&child->ptrace_entry));
+ list_add(&child->ptrace_entry, &new_parent->ptraced);
+ child->parent = new_parent;
+ child->ptracer_cred = get_cred(ptracer_cred);
+}
+
/*
* ptrace a task: make the debugger its new parent and
* move it to the ptrace list.
*
* Must be called with the tasklist lock write-held.
*/
-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)
{
- 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));
+ __ptrace_link(child, new_parent, __task_cred(new_parent));
rcu_read_unlock();
}
@@ -383,7 +389,7 @@ static int ptrace_attach(struct task_struct *task, long request,
flags |= PT_SEIZED;
task->ptrace = flags;
- __ptrace_link(task, current);
+ ptrace_link(task, current);
/* SEIZE doesn't trap tracee on attach */
if (!seize)
@@ -456,7 +462,7 @@ static int ptrace_traceme(void)
*/
if (!ret && !(current->real_parent->flags & PF_EXITING)) {
current->ptrace = PT_PTRACED;
- __ptrace_link(current, current->real_parent);
+ ptrace_link(current, current->real_parent);
}
}
write_unlock_irq(&tasklist_lock);