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Date: Tue, 23 May 2017 14:50:04 +0200 From: Takashi Iwai <tiwai@...e.de> To: ebiederm@...ssion.com (Eric W. Biederman) Cc: linux-kernel@...r.kernel.org Subject: Re: [CFT][PATCH] ptrace: Properly initialize ptracer_cred on fork On Tue, 23 May 2017 14:40:58 +0200, Eric W. Biederman wrote: > > Takashi Iwai <tiwai@...e.de> writes: > > > On Tue, 23 May 2017 07:47:32 +0200, > > Takashi Iwai wrote: > >> > >> On Mon, 22 May 2017 23:04:48 +0200, > >> Eric W. Biederman wrote: > >> > > >> > > >> > 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. > >> > > >> > Fixes: 64b875f7ac8a ("ptrace: Capture the ptracer's creds not PT_PTRACE_CAP") > >> > Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com> > >> > --- > >> > > >> > If I could get some folks to test and verify this fixes the > >> > enlightenment issue I would really appreciate it. > >> > >> This seems giving a compile warning and it becomes error in the > >> following: > >> > >> In file included from ./include/linux/mutex.h:13:0, > >> from ./include/linux/kernfs.h:13, > >> from ./include/linux/sysfs.h:15, > >> from ./include/linux/kobject.h:21, > >> from ./include/linux/device.h:17, > >> from drivers/gpu/drm/i915/gvt/kvmgt.c:32: > >> ./include/linux/ptrace.h: In function ‘ptrace_init_task’: > >> ./arch/x86/include/asm/current.h:17:17: error: passing argument 3 of ‘__ptrace_link’ discards ‘const’ qualifier from pointer target type [-Werror=discarded-qualifiers] > >> #define current get_current() > >> ^ > >> ./include/linux/ptrace.h:210:41: note: in expansion of macro ‘current’ > >> __ptrace_link(child, current->parent, current->ptracer_cred); > >> ^~~~~~~ > >> In file included from ./arch/x86/include/asm/stacktrace.h:10:0, > >> from ./arch/x86/include/asm/perf_event.h:246, > >> from ./include/linux/perf_event.h:24, > >> from ./arch/x86/include/asm/kvm_host.h:24, > >> from ./include/linux/kvm_host.h:37, > >> from drivers/gpu/drm/i915/gvt/kvmgt.c:41: > >> ./include/linux/ptrace.h:56:13: note: expected ‘struct cred *’ but argument is of type ‘const struct cred *’ > >> extern void __ptrace_link(struct task_struct *child, > >> ^~~~~~~~~~~~~ > >> cc1: all warnings being treated as errors > > > > Through a quick test on VM (fixed patch by adding const to > > __ptrace_link() argument), it seems working fine. > > Thank you. It seems when I fixed the const issue in my tree I forget > commit --amend so the fix didn't make it into the patch I sent out. > > > Tested-by: Takashi Iwai <tiwai@...e.de> > > Just to confirm. You were able to reproduce the enlightenment failure > and this fixes it? Yes. It was reproducible on KVM image. Takashi
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