3.16.52-rc1 review patch. If anyone has any objections, please let me know.
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From: "Eric W. Biederman" ebiederm@xmission.com
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: Ben Hutchings ben@decadent.org.uk --- include/linux/ptrace.h | 7 +++++-- kernel/ptrace.c | 20 +++++++++++++------- 2 files changed, 18 insertions(+), 9 deletions(-)
--- a/include/linux/ptrace.h +++ b/include/linux/ptrace.h @@ -52,7 +52,8 @@ extern int ptrace_request(struct task_st 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); #define PTRACE_MODE_READ 0x01 @@ -204,7 +205,7 @@ static inline void ptrace_init_task(stru
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); @@ -213,6 +214,8 @@ static inline void ptrace_init_task(stru
set_tsk_thread_flag(child, TIF_SIGPENDING); } + else + child->ptracer_cred = NULL; }
/** --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -63,19 +63,25 @@ static int ptrace_trapping_sleep_fn(void return 0; }
+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(); }
@@ -387,7 +393,7 @@ static int ptrace_attach(struct task_str flags |= PT_SEIZED; task->ptrace = flags;
- __ptrace_link(task, current); + ptrace_link(task, current);
/* SEIZE doesn't trap tracee on attach */ if (!seize) @@ -454,7 +460,7 @@ 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);