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Filename Latest commit message Latest commit date
Jesper Dangaard Brouer 42c83e3bca bpf: Remove MTU check in __bpf_skb_max_len
commit 6306c1189e77a513bf02720450bb43bd4ba5d8ae upstream.

Multiple BPF-helpers that can manipulate/increase the size of the SKB uses
__bpf_skb_max_len() as the max-length. This function limit size against
the current net_device MTU (skb->dev->mtu).

When a BPF-prog grow the packet size, then it should not be limited to the
MTU. The MTU is a transmit limitation, and software receiving this packet
should be allowed to increase the size. Further more, current MTU check in
__bpf_skb_max_len uses the MTU from ingress/current net_device, which in
case of redirects uses the wrong net_device.

This patch keeps a sanity max limit of SKB_MAX_ALLOC (16KiB). The real limit
is elsewhere in the system. Jesper's testing[1] showed it was not possible
to exceed 8KiB when expanding the SKB size via BPF-helper. The limiting
factor is the define KMALLOC_MAX_CACHE_SIZE which is 8192 for
SLUB-allocator (CONFIG_SLUB) in-case PAGE_SIZE is 4096. This define is
in-effect due to this being called from softirq context see code
__gfp_pfmemalloc_flags() and __do_kmalloc_node(). Jakub's testing showed
that frames above 16KiB can cause NICs to reset (but not crash). Keep this
sanity limit at this level as memory layer can differ based on kernel
config.

[1] https://github.com/xdp-project/bpf-examples/tree/master/MTU-tests

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/161287788936.790810.2937823995775097177.stgit@firesoul
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2021-04-07 14:47:41 +02:00
arch powerpc: Force inlining of cpu_has_feature() to avoid build failure 2021-04-07 14:47:39 +02:00
block block: recalculate segment count for multi-segment discards correctly 2021-03-30 14:35:28 +02:00
certs
crypto crypto: x86 - Regularize glue function prototypes 2021-03-20 10:39:47 +01:00
Documentation KVM: arm64: Reject VM creation when the default IPA size is unsupported 2021-03-17 17:03:57 +01:00
drivers net: wan/lmc: unregister device when no matching device is found 2021-04-07 14:47:41 +02:00
fs ext4: do not iput inode under running transaction in ext4_rename() 2021-04-07 14:47:40 +02:00
include net: introduce CAN specific pointer in the struct net_device 2021-04-07 14:47:41 +02:00
init
ipc
kernel locking/ww_mutex: Simplify use_ww_ctx & ww_ctx handling 2021-04-07 14:47:40 +02:00
lib
LICENSES
mm hugetlbfs: hugetlb_fault_mutex_hash() cleanup 2021-03-30 14:35:19 +02:00
net bpf: Remove MTU check in __bpf_skb_max_len 2021-04-07 14:47:41 +02:00
samples
scripts
security integrity: double check iint_cache was initialized 2021-03-30 14:35:24 +02:00
sound ASoC: rt5659: Update MCLK rate in set_sysclk() 2021-04-07 14:47:40 +02:00
tools flow_dissector: fix TTL and TOS dissection on IPv4 fragments 2021-04-07 14:47:40 +02:00
usr
virt KVM: arm64: Ensure I-cache isolation between vcpus of a same VM 2021-03-17 17:03:57 +01:00
.clang-format
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore
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COPYING
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Kbuild
Kconfig
MAINTAINERS
Makefile Linux 5.4.109 2021-03-30 14:35:30 +02:00
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.