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ptrace: Properly initialize ptracer_cred on fork 

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: 64b875f7ac ("ptrace: Capture the ptracer's creds not PT_PTRACE_CAP")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman 2017-05-22 15:40:12 -05:00
parent 3fd3722621
commit c70d9d809f
2 changed files with 18 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
include/linux/ptrace.h
View File

@ -54,7 +54,8 @@ 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
@ -206,7 +207,7 @@ 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);
@ -215,6 +216,8 @@ static inline void ptrace_init_task(struct task_struct *child, bool ptrace)
set_tsk_thread_flag(child, TIF_SIGPENDING);
}
else
child->ptracer_cred = NULL;
}
/**

20
kernel/ptrace.c
View File

@ -60,19 +60,25 @@ 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();
}
@ -386,7 +392,7 @@ 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)
@ -459,7 +465,7 @@ 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);