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Shmulik Ladkani 3dcbdb134f net: gso: Fix skb_segment splat when splitting gso_size mangled skb having linear-headed frag_list 
Historically, support for frag_list packets entering skb_segment() was
limited to frag_list members terminating on exact same gso_size
boundaries. This is verified with a BUG_ON since commit 89319d3801
("net: Add frag_list support to skb_segment"), quote:

    As such we require all frag_list members terminate on exact MSS
    boundaries.  This is checked using BUG_ON.
    As there should only be one producer in the kernel of such packets,
    namely GRO, this requirement should not be difficult to maintain.

However, since commit 6578171a7f ("bpf: add bpf_skb_change_proto helper"),
the "exact MSS boundaries" assumption no longer holds:
An eBPF program using bpf_skb_change_proto() DOES modify 'gso_size', but
leaves the frag_list members as originally merged by GRO with the
original 'gso_size'. Example of such programs are bpf-based NAT46 or
NAT64.

This lead to a kernel BUG_ON for flows involving:
 - GRO generating a frag_list skb
 - bpf program performing bpf_skb_change_proto() or bpf_skb_adjust_room()
 - skb_segment() of the skb

See example BUG_ON reports in [0].

In commit 13acc94eff ("net: permit skb_segment on head_frag frag_list skb"),
skb_segment() was modified to support the "gso_size mangling" case of
a frag_list GRO'ed skb, but *only* for frag_list members having
head_frag==true (having a page-fragment head).

Alas, GRO packets having frag_list members with a linear kmalloced head
(head_frag==false) still hit the BUG_ON.

This commit adds support to skb_segment() for a 'head_skb' packet having
a frag_list whose members are *non* head_frag, with gso_size mangled, by
disabling SG and thus falling-back to copying the data from the given
'head_skb' into the generated segmented skbs - as suggested by Willem de
Bruijn [1].

Since this approach involves the penalty of skb_copy_and_csum_bits()
when building the segments, care was taken in order to enable this
solution only when required:
 - untrusted gso_size, by testing SKB_GSO_DODGY is set
   (SKB_GSO_DODGY is set by any gso_size mangling functions in
    net/core/filter.c)
 - the frag_list is non empty, its item is a non head_frag, *and* the
   headlen of the given 'head_skb' does not match the gso_size.

[0]
https://lore.kernel.org/netdev/20190826170724.25ff616f@pixies/
https://lore.kernel.org/netdev/9265b93f-253d-6b8c-f2b8-4b54eff1835c@fb.com/

[1]
https://lore.kernel.org/netdev/CA+FuTSfVsgNDi7c=GUU8nMg2hWxF2SjCNLXetHeVPdnxAW5K-w@mail.gmail.com/

Fixes: 6578171a7f ("bpf: add bpf_skb_change_proto helper")
Suggested-by: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Alexander Duyck <alexander.duyck@gmail.com>
Signed-off-by: Shmulik Ladkani <shmulik.ladkani@gmail.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
 		2019-09-07 17:58:48 +02:00
Documentation Char/Misc driver fixes for 5.3-rc7 2019-09-02 09:30:34 -07:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
arch Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2019-09-01 11:21:57 -07:00
block block: remove REQ_NOWAIT_INLINE 2019-08-15 11:09:16 -06:00
certs Revert "Merge tag 'keys-acl-20190703' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs" 2019-07-10 18:43:43 -07:00
crypto USB / PHY patches for 5.3-rc1 2019-07-11 15:40:06 -07:00
drivers isdn/capi: check message length in capi_write() 2019-09-07 17:44:25 +02:00
fs a few small SMB3 fixes, and a larger one to fix various older string handling functions 2019-08-29 17:51:23 -07:00
include isdn/capi: check message length in capi_write() 2019-09-07 17:44:25 +02:00
init Merge branch 'work.mount0' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2019-07-19 10:42:02 -07:00
ipc Merge branch 'work.mount0' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2019-07-19 10:42:02 -07:00
kernel bpf: fix precision tracking of stack slots 2019-09-05 14:06:58 +02:00
lib Partially revert "kfifo: fix kfifo_alloc() and kfifo_init()" 2019-08-30 18:47:15 -07:00
mm mm: memcontrol: fix percpu vmstats and vmevents flush 2019-08-30 18:00:50 -07:00
net net: gso: Fix skb_segment splat when splitting gso_size mangled skb having linear-headed frag_list 2019-09-07 17:58:48 +02:00
samples auxdisplay: Fix a typo in cfag12864b-example.c 2019-08-08 20:00:18 +02:00
scripts SPDX fixes for 5.3-rc5 2019-08-18 09:26:16 -07:00
security keys: ensure that ->match_free() is called in request_key_and_link() 2019-08-30 11:10:55 -07:00
sound sound fixes for 5.3-rc7 2019-08-27 10:42:03 -07:00
tools Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/klassert/ipsec 2019-09-06 15:09:16 +02:00
usr kbuild: enable arch/s390/include/uapi/asm/zcrypt.h for uapi header test 2019-07-23 10:45:46 +02:00
virt arm64 fixes for -rc7 2019-08-28 10:37:21 -07:00
.clang-format Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2019-04-17 11:26:25 -07:00
.cocciconfig
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.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore .gitignore: Add compilation database file 2019-07-27 12:18:19 +09:00
.mailmap mailmap: add aliases for Dmitry Safonov 2019-08-30 18:00:50 -07:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS Remove references to dead website. 2019-07-19 12:22:04 -07:00
Kbuild Kbuild updates for v5.1 2019-03-10 17:48:21 -07:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS MAINTAINERS: add myself as maintainer for xilinx axiethernet driver 2019-09-06 15:17:16 +02:00
Makefile Linux 5.3-rc7 2019-09-02 09:57:40 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

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

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

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.