linux/kernel/bpf
Jesper Dangaard Brouer 676e4a6fe7 xdp: fix cpumap redirect SKB creation bug
We want to avoid leaking pointer info from xdp_frame (that is placed in
top of frame) like commit 6dfb970d3d ("xdp: avoid leaking info stored in
frame data on page reuse"), and followup commit 97e19cce05 ("bpf:
reserve xdp_frame size in xdp headroom") that reserve this headroom.

These changes also affected how cpumap constructed SKBs, as xdpf->headroom
size changed, the skb data starting point were in-effect shifted with 32
bytes (sizeof xdp_frame). This was still okay, as the cpumap frame_size
calculation also included xdpf->headroom which were reduced by same amount.

A bug was introduced in commit 77ea5f4cbe ("bpf/cpumap: make sure
frame_size for build_skb is aligned if headroom isn't"), where the
xdpf->headroom became part of the SKB_DATA_ALIGN rounding up. This
round-up to find the frame_size is in principle still correct as it does
not exceed the 2048 bytes frame_size (which is max for ixgbe and i40e),
but the 32 bytes offset of pkt_data_start puts this over the 2048 bytes
limit. This cause skb_shared_info to spill into next frame. It is a little
hard to trigger, as the SKB need to use above 15 skb_shinfo->frags[] as
far as I calculate. This does happen in practise for TCP streams when
skb_try_coalesce() kicks in.

KASAN can be used to detect these wrong memory accesses, I've seen:
 BUG: KASAN: use-after-free in skb_try_coalesce+0x3cb/0x760
 BUG: KASAN: wild-memory-access in skb_release_data+0xe2/0x250

Driver veth also construct a SKB from xdp_frame in this way, but is not
affected, as it doesn't reserve/deduct the room (used by xdp_frame) from
the SKB headroom. Instead is clears the pointers via xdp_scrub_frame(),
and allows SKB to use this area.

The fix in this patch is to do like veth and instead allow SKB to (re)use
the area occupied by xdp_frame, by clearing via xdp_scrub_frame().  (This
does kill the idea of the SKB being able to access (mem) info from this
area, but I guess it was a bad idea anyhow, and it was already killed by
the veth changes.)

Fixes: 77ea5f4cbe ("bpf/cpumap: make sure frame_size for build_skb is aligned if headroom isn't")
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
2019-03-29 12:15:02 -07:00
..
arraymap.c bpf: introduce BPF_F_LOCK flag 2019-02-01 20:55:39 +01:00
bpf_lru_list.c bpf: lru: Lower the PERCPU_NR_SCANS from 16 to 4 2017-04-17 13:55:52 -04:00
bpf_lru_list.h bpf: Only set node->ref = 1 if it has not been set 2017-09-01 09:57:39 -07:00
btf.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2019-02-08 15:00:17 -08:00
cgroup.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2019-02-08 15:00:17 -08:00
core.c Merge branch 'perf-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2019-03-06 07:59:36 -08:00
cpumap.c xdp: fix cpumap redirect SKB creation bug 2019-03-29 12:15:02 -07:00
devmap.c bpf: devmap: fix wrong interface selection in notifier_call 2018-10-26 00:32:21 +02:00
disasm.c bpf: disassembler support JMP32 2019-01-26 13:33:01 -08:00
disasm.h bpf: Remove struct bpf_verifier_env argument from print_bpf_insn 2018-03-23 17:38:57 +01:00
hashtab.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2019-02-08 15:00:17 -08:00
helpers.c bpf: introduce BPF_F_LOCK flag 2019-02-01 20:55:39 +01:00
inode.c bpf: fix use after free in bpf_evict_inode 2019-03-26 01:38:49 +01:00
local_storage.c bpf: introduce BPF_F_LOCK flag 2019-02-01 20:55:39 +01:00
lpm_trie.c bpf, lpm: fix lookup bug in map_delete_elem 2019-02-22 16:17:53 +01:00
Makefile bpf: add queue and stack maps 2018-10-19 13:24:31 -07:00
map_in_map.c bpf: set inner_map_meta->spin_lock_off correctly 2019-02-27 17:03:13 -08:00
map_in_map.h bpf: Add syscall lookup support for fd array and htab 2017-06-29 13:13:25 -04:00
offload.c bpf: offload: add priv field for drivers 2019-02-12 17:07:09 +01:00
percpu_freelist.c bpf: fix lockdep false positive in percpu_freelist 2019-01-31 23:18:21 +01:00
percpu_freelist.h bpf: fix lockdep false positive in percpu_freelist 2019-01-31 23:18:21 +01:00
queue_stack_maps.c bpf: fix integer overflow in queue_stack_map 2018-11-22 21:29:40 +01:00
reuseport_array.c bpf: Introduce BPF_MAP_TYPE_REUSEPORT_SOCKARRAY 2018-08-11 01:58:46 +02:00
stackmap.c bpf: fix lockdep false positive in stackmap 2019-02-11 16:36:24 +01:00
syscall.c bpf: Try harder when allocating memory for large maps 2019-03-18 16:48:25 +01:00
tnum.c bpf/verifier: improve register value range tracking with ARSH 2018-04-29 08:45:53 -07:00
verifier.c bpf: remove incorrect 'verifier bug' warning 2019-03-26 13:02:16 -07:00
xskmap.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2018-10-19 11:03:06 -07:00