Re: CVE-2024-50219: mm/page_alloc: let GFP_ATOMIC order-0 allocs access highatomic reserves

[Vlastimil Babka <vbabka@suse.cz>]

On 11/9/24 11:15, Greg Kroah-Hartman wrote:
> Description
> ===========
> 
> In the Linux kernel, the following vulnerability has been resolved:
> 
> mm/page_alloc: let GFP_ATOMIC order-0 allocs access highatomic reserves
> 
> Under memory pressure it's possible for GFP_ATOMIC order-0 allocations to
> fail even though free pages are available in the highatomic reserves. 
> GFP_ATOMIC allocations cannot trigger unreserve_highatomic_pageblock()
> since it's only run from reclaim.
> 
> Given that such allocations will pass the watermarks in
> __zone_watermark_unusable_free(), it makes sense to fallback to highatomic
> reserves the same way that ALLOC_OOM can.
> 
> This fixes order-0 page allocation failures observed on Cloudflare's fleet
> when handling network packets:

Hi,

I would like to dispute the CVE. GFP_ATOMIC page allocations failures can
generally happen (typically from network receive path, like here) and should
always have a fallback. The impact could be somewhat worse performance at
worst. AFAIK they are not affected by panic_on_warn nor panic_on_oom either,
it's a pr_warn(), so I don't think there's a DoS vector.

It would be also nice to adjust any automatic flagging to distinguish this
for the future.

Thanks,
Vlastimil

>   kswapd1: page allocation failure: order:0, mode:0x820(GFP_ATOMIC),
>   nodemask=(null),cpuset=/,mems_allowed=0-7
>   CPU: 10 PID: 696 Comm: kswapd1 Kdump: loaded Tainted: G           O 6.6.43-CUSTOM #1
>   Hardware name: MACHINE
>   Call Trace:
>    <IRQ>
>    dump_stack_lvl+0x3c/0x50
>    warn_alloc+0x13a/0x1c0
>    __alloc_pages_slowpath.constprop.0+0xc9d/0xd10
>    __alloc_pages+0x327/0x340
>    __napi_alloc_skb+0x16d/0x1f0
>    bnxt_rx_page_skb+0x96/0x1b0 [bnxt_en]
>    bnxt_rx_pkt+0x201/0x15e0 [bnxt_en]
>    __bnxt_poll_work+0x156/0x2b0 [bnxt_en]
>    bnxt_poll+0xd9/0x1c0 [bnxt_en]
>    __napi_poll+0x2b/0x1b0
>    bpf_trampoline_6442524138+0x7d/0x1000
>    __napi_poll+0x5/0x1b0
>    net_rx_action+0x342/0x740
>    handle_softirqs+0xcf/0x2b0
>    irq_exit_rcu+0x6c/0x90
>    sysvec_apic_timer_interrupt+0x72/0x90
>    </IRQ>
> 
> [mfleming@cloudflare.com: update comment]
>   Link: https://lkml.kernel.org/r/20241015125158.3597702-1-matt@readmodwrite.com
> 
> The Linux kernel CVE team has assigned CVE-2024-50219 to this issue.
> 
> 
> Affected and fixed versions
> ===========================
> 
> 	Issue introduced in 5.9 with commit 1d91df85f399 and fixed in 5.15.171 with commit 4c4e238d3ada
> 	Issue introduced in 5.9 with commit 1d91df85f399 and fixed in 6.1.116 with commit 189b954469cf
> 	Issue introduced in 5.9 with commit 1d91df85f399 and fixed in 6.6.60 with commit b958948ae1cb
> 	Issue introduced in 5.9 with commit 1d91df85f399 and fixed in 6.11.7 with commit d0fdacfb85a3
> 	Issue introduced in 5.9 with commit 1d91df85f399 and fixed in 6.12-rc6 with commit 281dd25c1a01
> 
> Please see https://www.kernel.org for a full list of currently supported
> kernel versions by the kernel community.
> 
> Unaffected versions might change over time as fixes are backported to
> older supported kernel versions.  The official CVE entry at
> 	https://cve.org/CVERecord/?id=CVE-2024-50219
> will be updated if fixes are backported, please check that for the most
> up to date information about this issue.
> 
> 
> Affected files
> ==============
> 
> The file(s) affected by this issue are:
> 	mm/page_alloc.c
> 
> 
> Mitigation
> ==========
> 
> The Linux kernel CVE team recommends that you update to the latest
> stable kernel version for this, and many other bugfixes.  Individual
> changes are never tested alone, but rather are part of a larger kernel
> release.  Cherry-picking individual commits is not recommended or
> supported by the Linux kernel community at all.  If however, updating to
> the latest release is impossible, the individual changes to resolve this
> issue can be found at these commits:
> 	https://git.kernel.org/stable/c/4c4e238d3adad3c94bb255d0f117d3685bbfdd33
> 	https://git.kernel.org/stable/c/189b954469cf82f8b8cf496f8de94b006d2d4746
> 	https://git.kernel.org/stable/c/b958948ae1cb3e39c48e9f805436fd652103c71e
> 	https://git.kernel.org/stable/c/d0fdacfb85a3e1223b894cc6e60091ec91049e9e
> 	https://git.kernel.org/stable/c/281dd25c1a018261a04d1b8bf41a0674000bfe38
>