Merge tag 'v3.5'

Linux 3.5

* tag 'v3.5': (1242 commits)
  Linux 3.5
  Remove SYSTEM_SUSPEND_DISK system state
  kdb: Switch to nolock variants of kmsg_dump functions
  printk: Implement some unlocked kmsg_dump functions
  printk: Remove kdb_syslog_data
  kdb: Revive dmesg command
  dm raid1: set discard_zeroes_data_unsupported
  dm thin: do not send discards to shared blocks
  dm raid1: fix crash with mirror recovery and discard
  pnfs-obj: Fix __r4w_get_page when offset is beyond i_size
  pnfs-obj: don't leak objio_state if ore_write/read fails
  ore: Unlock r4w pages in exact reverse order of locking
  ore: Remove support of partial IO request (NFS crash)
  ore: Fix NFS crash by supporting any unaligned RAID IO
  UBIFS: fix a bug in empty space fix-up
  cx25821: Remove bad strcpy to read-only char*
  HID: hid-multitouch: add support for Zytronic panels
  MIPS: PCI: Move fixups from __init to __devinit.
  MIPS: Fix bug.h MIPS build regression
  MIPS: sync-r4k: remove redundant irq operation
  ...

1 files changed, 57 insertions, 0 deletions

diff --git a/Documentation/prctl/no_new_privs.txt b/Documentation/prctl/no_new_privs.txt
new file mode 100644
index 000000000000..f7be84fba910
--- /dev/null
+++ b/Documentation/prctl/no_new_privs.txt
@@ -0,0 +1,57 @@
+The execve system call can grant a newly-started program privileges that
+its parent did not have.  The most obvious examples are setuid/setgid
+programs and file capabilities.  To prevent the parent program from
+gaining these privileges as well, the kernel and user code must be
+careful to prevent the parent from doing anything that could subvert the
+child.  For example:
+
+ - The dynamic loader handles LD_* environment variables differently if
+   a program is setuid.
+
+ - chroot is disallowed to unprivileged processes, since it would allow
+   /etc/passwd to be replaced from the point of view of a process that
+   inherited chroot.
+
+ - The exec code has special handling for ptrace.
+
+These are all ad-hoc fixes.  The no_new_privs bit (since Linux 3.5) is a
+new, generic mechanism to make it safe for a process to modify its
+execution environment in a manner that persists across execve.  Any task
+can set no_new_privs.  Once the bit is set, it is inherited across fork,
+clone, and execve and cannot be unset.  With no_new_privs set, execve
+promises not to grant the privilege to do anything that could not have
+been done without the execve call.  For example, the setuid and setgid
+bits will no longer change the uid or gid; file capabilities will not
+add to the permitted set, and LSMs will not relax constraints after
+execve.
+
+To set no_new_privs, use prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0).
+
+Be careful, though: LSMs might also not tighten constraints on exec
+in no_new_privs mode.  (This means that setting up a general-purpose
+service launcher to set no_new_privs before execing daemons may
+interfere with LSM-based sandboxing.)
+
+Note that no_new_privs does not prevent privilege changes that do not
+involve execve.  An appropriately privileged task can still call
+setuid(2) and receive SCM_RIGHTS datagrams.
+
+There are two main use cases for no_new_privs so far:
+
+ - Filters installed for the seccomp mode 2 sandbox persist across
+   execve and can change the behavior of newly-executed programs.
+   Unprivileged users are therefore only allowed to install such filters
+   if no_new_privs is set.
+
+ - By itself, no_new_privs can be used to reduce the attack surface
+   available to an unprivileged user.  If everything running with a
+   given uid has no_new_privs set, then that uid will be unable to
+   escalate its privileges by directly attacking setuid, setgid, and
+   fcap-using binaries; it will need to compromise something without the
+   no_new_privs bit set first.
+
+In the future, other potentially dangerous kernel features could become
+available to unprivileged tasks if no_new_privs is set.  In principle,
+several options to unshare(2) and clone(2) would be safe when
+no_new_privs is set, and no_new_privs + chroot is considerable less
+dangerous than chroot by itself.