Merge branch 'linux-linaro-lsk-v4.4-android' of git://git.linaro.org/kernel/linux-linaro-stable.git

* linux-linaro-lsk-v4.4-android: (812 commits)
  Linux 4.4.167
  mac80211: ignore NullFunc frames in the duplicate detection
  mac80211: fix reordering of buffered broadcast packets
  mac80211: ignore tx status for PS stations in ieee80211_tx_status_ext
  mac80211: Clear beacon_int in ieee80211_do_stop
  mac80211_hwsim: Timer should be initialized before device registered
  kgdboc: fix KASAN global-out-of-bounds bug in param_set_kgdboc_var()
  tty: serial: 8250_mtk: always resume the device in probe.
  cifs: Fix separator when building path from dentry
  Staging: lustre: remove two build warnings
  xhci: Prevent U1/U2 link pm states if exit latency is too long
  SUNRPC: Fix leak of krb5p encode pages
  virtio/s390: fix race in ccw_io_helper()
  virtio/s390: avoid race on vcdev->config
  ALSA: pcm: Fix interval evaluation with openmin/max
  ALSA: pcm: Call snd_pcm_unlink() conditionally at closing
  ALSA: pcm: Fix starvation on down_write_nonblock()
  ALSA: hda: Add support for AMD Stoney Ridge
  ALSA: usb-audio: Fix UAF decrement if card has no live interfaces in card.c
  USB: check usb_get_extra_descriptor for proper size
  ...

Conflicts:
	drivers/gpu/drm/rockchip/rockchip_drm_drv.c
	drivers/usb/host/xhci-ring.c

Change-Id: I4304b0875908403a7d88a0d77da52cea04563c11

1 files changed, 14 insertions, 0 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index d1a675d32320..d780651a760c 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -472,6 +472,20 @@ static int proc_pid_stack(struct seq_file *m, struct pid_namespace *ns,
 	int err;
 	int i;
 
+	/*
+	 * The ability to racily run the kernel stack unwinder on a running task
+	 * and then observe the unwinder output is scary; while it is useful for
+	 * debugging kernel issues, it can also allow an attacker to leak kernel
+	 * stack contents.
+	 * Doing this in a manner that is at least safe from races would require
+	 * some work to ensure that the remote task can not be scheduled; and
+	 * even then, this would still expose the unwinder as local attack
+	 * surface.
+	 * Therefore, this interface is restricted to root.
+	 */
+	if (!file_ns_capable(m->file, &init_user_ns, CAP_SYS_ADMIN))
+		return -EACCES;
+
 	entries = kmalloc(MAX_STACK_TRACE_DEPTH * sizeof(*entries), GFP_KERNEL);
 	if (!entries)
 		return -ENOMEM;