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Jakub Kicinski 28e33f9d78 bpf: disallow arithmetic operations on context pointer 
Commit f1174f77b5 ("bpf/verifier: rework value tracking")
removed the crafty selection of which pointer types are
allowed to be modified.  This is OK for most pointer types
since adjust_ptr_min_max_vals() will catch operations on
immutable pointers.  One exception is PTR_TO_CTX which is
now allowed to be offseted freely.

The intent of aforementioned commit was to allow context
access via modified registers.  The offset passed to
->is_valid_access() verifier callback has been adjusted
by the value of the variable offset.

What is missing, however, is taking the variable offset
into account when the context register is used.  Or in terms
of the code adding the offset to the value passed to the
->convert_ctx_access() callback.  This leads to the following
eBPF user code:

     r1 += 68
     r0 = *(u32 *)(r1 + 8)
     exit

being translated to this in kernel space:

   0: (07) r1 += 68
   1: (61) r0 = *(u32 *)(r1 +180)
   2: (95) exit

Offset 8 is corresponding to 180 in the kernel, but offset
76 is valid too.  Verifier will "accept" access to offset
68+8=76 but then "convert" access to offset 8 as 180.
Effective access to offset 248 is beyond the kernel context.
(This is a __sk_buff example on a debug-heavy kernel -
packet mark is 8 -> 180, 76 would be data.)

Dereferencing the modified context pointer is not as easy
as dereferencing other types, because we have to translate
the access to reading a field in kernel structures which is
usually at a different offset and often of a different size.
To allow modifying the pointer we would have to make sure
that given eBPF instruction will always access the same
field or the fields accessed are "compatible" in terms of
offset and size...

Disallow dereferencing modified context pointers and add
to selftests the test case described here.

Fixes: f1174f77b5 ("bpf/verifier: rework value tracking")
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2017-10-18 13:21:13 +01:00
arch Merge branch 'ppc-bundle' (bundle from Michael Ellerman) 2017-10-09 19:08:32 -07:00
block bsg-lib: fix use-after-free under memory-pressure 2017-10-04 08:35:04 -06:00
certs modsign: add markers to endif-statements in certs/Makefile 2017-07-14 11:01:37 +10:00
crypto crypto: af_alg - update correct dst SGL entry 2017-09-20 17:42:42 +08:00
Documentation Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2017-10-09 16:25:00 -07:00
drivers ibmvnic: Fix calculation of number of TX header descriptors 2017-10-18 12:20:39 +01:00
firmware firmware: Restore support for built-in firmware 2017-09-16 10:58:48 -07:00
fs NFS client bugfixes for Linux 4.14 2017-10-09 10:55:37 -07:00
include tun: call dev_get_valid_name() before register_netdevice() 2017-10-16 21:02:54 +01:00
init Merge branch 'work.mount' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2017-09-14 18:54:01 -07:00
ipc fix a typo in put_compat_shm_info() 2017-09-25 20:41:46 -04:00
kernel bpf: disallow arithmetic operations on context pointer 2017-10-18 13:21:13 +01:00
lib lib/ratelimit.c: use deferred printk() version 2017-10-03 17:54:26 -07:00
mm net: memcontrol: defer call to mem_cgroup_sk_alloc() 2017-10-09 20:55:01 -07:00
net netlink: fix netlink_ack() extack race 2017-10-18 12:22:28 +01:00
samples media updates for v4.14-rc1 2017-09-07 12:53:14 -07:00
scripts checkpatch: fix ignoring cover-letter logic 2017-10-03 17:54:26 -07:00
security lsm: fix smack_inode_removexattr and xattr_getsecurity memleak 2017-10-04 18:03:15 +11:00
sound sound fixes for 4.14-rc4 2017-10-05 10:39:29 -07:00
tools bpf: disallow arithmetic operations on context pointer 2017-10-18 13:21:13 +01:00
usr ramfs: clarify help text that compression applies to ramfs as well as legacy ramdisk. 2017-07-06 16:24:30 -07:00
virt Revert "KVM: Don't accept obviously wrong gsi values via KVM_IRQFD" 2017-09-19 08:37:17 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore kbuild: Add support to generate LLVM assembly files 2017-04-25 08:13:52 +09:00
.mailmap Update James Hogan's email address 2017-10-04 17:11:53 -07:00
COPYING
CREDITS selinux/stable-4.14 PR 20170831 2017-09-12 13:21:00 -07:00
Kbuild kbuild: Consolidate header generation from ASM offset information 2017-04-13 05:43:37 +09:00
Kconfig
MAINTAINERS ARC udpates for 4.14-rc4 2017-10-06 15:57:08 -07:00
Makefile Linux 4.14-rc4 2017-10-08 20:53:29 -07:00
README README: add a new README file, pointing to the Documentation/ 2016-10-24 08:12:35 -02:00

README 

Linux kernel
============

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.