diff options
author | Yunhong Jiang <yunhong.jiang@intel.com> | 2015-08-04 12:17:53 -0700 |
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committer | Yunhong Jiang <yunhong.jiang@intel.com> | 2015-08-04 15:44:42 -0700 |
commit | 9ca8dbcc65cfc63d6f5ef3312a33184e1d726e00 (patch) | |
tree | 1c9cafbcd35f783a87880a10f85d1a060db1a563 /kernel/Documentation/prctl/no_new_privs.txt | |
parent | 98260f3884f4a202f9ca5eabed40b1354c489b29 (diff) |
Add the rt linux 4.1.3-rt3 as base
Import the rt linux 4.1.3-rt3 as OPNFV kvm base.
It's from git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git linux-4.1.y-rt and
the base is:
commit 0917f823c59692d751951bf5ea699a2d1e2f26a2
Author: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Sat Jul 25 12:13:34 2015 +0200
Prepare v4.1.3-rt3
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
We lose all the git history this way and it's not good. We
should apply another opnfv project repo in future.
Change-Id: I87543d81c9df70d99c5001fbdf646b202c19f423
Signed-off-by: Yunhong Jiang <yunhong.jiang@intel.com>
Diffstat (limited to 'kernel/Documentation/prctl/no_new_privs.txt')
-rw-r--r-- | kernel/Documentation/prctl/no_new_privs.txt | 57 |
1 files changed, 57 insertions, 0 deletions
diff --git a/kernel/Documentation/prctl/no_new_privs.txt b/kernel/Documentation/prctl/no_new_privs.txt new file mode 100644 index 000000000..f7be84fba --- /dev/null +++ b/kernel/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. |