Описание
In the Linux kernel, the following vulnerability has been resolved:
ppp_async: drop the errored frame instead of resetting its headroom
ppp_receive_nonmp_frame() prepends a two-byte direction tag before running
the pass/active BPF filters:
*(__be16 )skb_push(skb, 2) = htons(PPP_FILTER_INBOUND_TAG);
Nothing on the receive path guarantees those two bytes of headroom. The
frame-error path in ppp_async's process_input_packet() resets a reused skb's
headroom to zero while claiming to restore it to a freshly allocated state -
but a fresh skb from dev_alloc_skb() carries NET_SKB_PAD:
err:
if (skb) {
/ make skb appear as freshly allocated */
skb_trim(skb, 0);
skb_reserve(skb, - skb_headroom(skb));
}
ap->rpkt still points at that skb, so the next frame is reassembled into it
with no headroom at all. A peer that sends a bad-FCS frame followed by one
beginning ff 03 then leaves a single byte of headroom by the time the filter
tag is pushed, which lands one byte below skb->head:
skbuff: skb_under_panic: len:49 put:2 head:ffff888003c10000
data:ffff888003c0ffff tail:0x30 end:0x640 dev:
kernel BUG at net/core/skbuff.c:214!
RIP: 0010:skb_panic+0x13e/0x230
Call Trace:
skb_push+0xbd/0x100
ppp_receive_nonmp_frame+0x48a/0x1d10
ppp_input+0x4e9/0x2f80
ppp_async_process+0x2a/0xe0
tasklet_action_common+0x20f/0x8a0
handle_softirqs+0x18e/0x590
Kernel panic - not syncing: Fatal exception in interrupt
Zeroing the headroom violates the NET_SKB_PAD guarantee that dev_alloc_skb()
gives the rest of the receive path. Besides the filter panic above, when CCP
compression is enabled ppp_decompress_frame() hands skb->data - 2 to
->decompress()/->incomp(), which then reads out of bounds before skb->head
for the same reason.
Rather than restore the headroom, drop the errored frame - as ppp_synctty
already does on its error path - and clear ap->rpkt so the next frame is
reassembled into a fresh skb with proper headroom. This is simpler and fixes
both the filter under-panic and the CCP out-of-bounds read.
The original V1 of this patch made room in ppp_receive_nonmp_frame() with
skb_cow_head(); Eric pointed out that fixing the root cause in the transport
is the right approach.
Found by fuzzing the PPP receive path with a mutating peer on a pty; it is an
interesting (remote) DoS: root configures PPP, the peer supplies two crashing
frames. The reproducer (repro-ppp-skb.c, unchanged from v1) panics in about a
second, and returns cleanly with this applied.
A flaw was found in the Linux kernel's Point-to-Point Protocol asynchronous (ppp_async) driver. When handling corrupted network frames, the driver improperly reuses packet buffers without preserving the required memory headroom. A connected peer can exploit this flaw by sending a sequence of crafted network frames, triggering an out-of-bounds memory read and a system crash, resulting in a Denial of Service (DoS).
Затронутые пакеты
| Платформа | Пакет | Состояние | Рекомендация | Релиз |
|---|---|---|---|---|
| Red Hat Enterprise Linux 10 | kernel | Fix deferred | ||
| Red Hat Enterprise Linux 6 | kernel | Not affected | ||
| Red Hat Enterprise Linux 7 | kernel | Fix deferred | ||
| Red Hat Enterprise Linux 7 | kernel-rt | Fix deferred | ||
| Red Hat Enterprise Linux 8 | kernel | Fix deferred | ||
| Red Hat Enterprise Linux 8 | kernel-rt | Fix deferred | ||
| Red Hat Enterprise Linux 9 | kernel | Fix deferred | ||
| Red Hat Enterprise Linux 9 | kernel-rt | Fix deferred | ||
| Red Hat OpenShift Container Platform 4 | openshift/ose-rhel-coreos-8 | Fix deferred | ||
| Red Hat OpenShift Container Platform 4 | openshift/ose-rhel-coreos-9 | Fix deferred |
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Дополнительная информация
Статус:
EPSS
5.5 Medium
CVSS3
Связанные уязвимости
In the Linux kernel, the following vulnerability has been resolved: ppp_async: drop the errored frame instead of resetting its headroom ppp_receive_nonmp_frame() prepends a two-byte direction tag before running the pass/active BPF filters: *(__be16 *)skb_push(skb, 2) = htons(PPP_FILTER_INBOUND_TAG); Nothing on the receive path guarantees those two bytes of headroom. The frame-error path in ppp_async's process_input_packet() resets a reused skb's headroom to zero while claiming to restore it to a freshly allocated state - but a fresh skb from dev_alloc_skb() carries NET_SKB_PAD: err: if (skb) { /* make skb appear as freshly allocated */ skb_trim(skb, 0); skb_reserve(skb, - skb_headroom(skb)); } ap->rpkt still points at that skb, so the next frame is reassembled into it with no headroom at all. A peer that sends a bad-FCS frame followed by one beginning ff 03 then leaves a single byte of headroom by the time the filter tag is pushed, which lands one byte below skb->head: skbuff: skb_u...
In the Linux kernel, the following vulnerability has been resolved: ppp_async: drop the errored frame instead of resetting its headroom ppp_receive_nonmp_frame() prepends a two-byte direction tag before running the pass/active BPF filters: *(__be16 *)skb_push(skb, 2) = htons(PPP_FILTER_INBOUND_TAG); Nothing on the receive path guarantees those two bytes of headroom. The frame-error path in ppp_async's process_input_packet() resets a reused skb's headroom to zero while claiming to restore it to a freshly allocated state - but a fresh skb from dev_alloc_skb() carries NET_SKB_PAD: err: if (skb) { /* make skb appear as freshly allocated */ skb_trim(skb, 0); skb_reserve(skb, - skb_headroom(skb)); } ap->rpkt still points at that skb, so the next frame is reassembled into it with no headroom at all. A peer that sends a bad-FCS frame followed by one beginning ff 03 then leaves a single byte of headroom by the time the filter tag is pushed, which lands one byte below skb->h
ppp_async: drop the errored frame instead of resetting its headroom
In the Linux kernel, the following vulnerability has been resolved: p ...
In the Linux kernel, the following vulnerability has been resolved: ppp_async: drop the errored frame instead of resetting its headroom ppp_receive_nonmp_frame() prepends a two-byte direction tag before running the pass/active BPF filters: *(__be16 *)skb_push(skb, 2) = htons(PPP_FILTER_INBOUND_TAG); Nothing on the receive path guarantees those two bytes of headroom. The frame-error path in ppp_async's process_input_packet() resets a reused skb's headroom to zero while claiming to restore it to a freshly allocated state - but a fresh skb from dev_alloc_skb() carries NET_SKB_PAD: err: if (skb) { /* make skb appear as freshly allocated */ skb_trim(skb, 0); skb_reserve(skb, - skb_headroom(skb)); } ap->rpkt still points at that skb, so the next frame is reassembled into it with no headroom at all. A peer that sends a bad-FCS frame followed by one beginning ff 03 then leaves a single byte of headroom by the time the filter tag is pushed, which lands one byte below skb...
EPSS
5.5 Medium
CVSS3