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Message-ID: <a4e4be39-b0e6-4632-878d-0765c9475984@redhat.com>
Date: Fri, 5 Sep 2025 15:07:06 +0200
From: David Hildenbrand <david@...hat.com>
To: Eric Dumazet <edumazet@...gle.com>,
 Naresh Kamboju <naresh.kamboju@...aro.org>
Cc: Netdev <netdev@...r.kernel.org>,
 "open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>,
 open list <linux-kernel@...r.kernel.org>, lkft-triage@...ts.linaro.org,
 Linux Regressions <regressions@...ts.linux.dev>,
 "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, Eric Biggers <ebiggers@...gle.com>,
 Dan Carpenter <dan.carpenter@...aro.org>, Arnd Bergmann <arnd@...db.de>,
 Ben Copeland <benjamin.copeland@...aro.org>,
 Anders Roxell <anders.roxell@...aro.org>, Shuah Khan <shuah@...nel.org>,
 Willem de Bruijn <willemb@...gle.com>, Pengtao He <hept.hept.hept@...il.com>
Subject: Re: next-20250905: x86_64: udpgso_bench.sh triggers NULL deref in
 zerocopy_fill_skb_from_iter

On 05.09.25 14:55, Eric Dumazet wrote:
> On Fri, Sep 5, 2025 at 2:30 AM Naresh Kamboju <naresh.kamboju@...aro.org> wrote:
>>
>> The following kernel crash was noticed on x86_64 running selftests net
>> udpgso_bench.sh
>> on Linux next-20250905 tag.
>>
>> Regression Analysis:
>> - New regression? yes
>> - Reproducibility? Re-validation is in progress
>>
>> First seen on next-20250905
>> Bad: next-20250905
>> Good: next-20250904
>>
>> Test regression: next-20250905 x86_64 selftests net BUG kernel NULL
>> pointer dereference zerocopy_fill_skb_from_iter
>>
>> Reported-by: Linux Kernel Functional Testing <lkft@...aro.org>
>>
>> x86_64:
>>   Test:
>>      * selftests: net: udpgso_bench.sh
>>
>> Test error:
>> selftests: net: udpgso_bench.sh
>> ipv4
>> tcp
>>
>> <trim>
>>
>> # tcp zerocopy
>> [  991.110488] SELinux: unrecognized netlink message: protocol=4
>> nlmsg_type=19 sclass=netlink_tcpdiag_socket pid=64835 comm=ss
>> # RTNETLINK answers: Invalid argument
>> [  991.129878] BUG: kernel NULL pointer dereference, address: 0000000000000008
>> [  991.136850] #PF: supervisor read access in kernel mode
>> [  991.141986] #PF: error_code(0x0000) - not-present page
>> [  991.147118] PGD 0 P4D 0
>> [  991.149657] Oops: Oops: 0000 [#1] SMP PTI
>> [  991.153661] CPU: 0 UID: 0 PID: 64842 Comm: udpgso_bench_tx Tainted:
>> G S                  6.17.0-rc4-next-20250905 #1 PREEMPT(voluntary)
>> [  991.165907] Tainted: [S]=CPU_OUT_OF_SPEC
>> [  991.169825] Hardware name: Supermicro SYS-5019S-ML/X11SSH-F, BIOS
>> 2.7 12/07/2021
>> [  991.177209] RIP: 0010:zerocopy_fill_skb_from_iter
>> (include/linux/page-flags.h:284)
>> [ 991.182954] Code: 4d 85 c0 0f 84 04 01 00 00 44 39 c7 41 0f 4d f8 4c
>> 63 de 4a 8b 54 dc 30 49 89 d6 4d 29 ce 49 c1 fe 06 49 d3 ee 4d 85 f6
>> 74 24 <48> 8b 4a 08 f6 c1 01 0f 85 cb 00 00 00 0f 1f 44 00 00 31 c9 48
>> f7
>> All code
>> ========
>>     0: 4d 85 c0              test   %r8,%r8
>>     3: 0f 84 04 01 00 00    je     0x10d
>>     9: 44 39 c7              cmp    %r8d,%edi
>>     c: 41 0f 4d f8          cmovge %r8d,%edi
>>    10: 4c 63 de              movslq %esi,%r11
>>    13: 4a 8b 54 dc 30        mov    0x30(%rsp,%r11,8),%rdx
>>    18: 49 89 d6              mov    %rdx,%r14
>>    1b: 4d 29 ce              sub    %r9,%r14
>>    1e: 49 c1 fe 06          sar    $0x6,%r14
>>    22: 49 d3 ee              shr    %cl,%r14
>>    25: 4d 85 f6              test   %r14,%r14
>>    28: 74 24                je     0x4e
>>    2a:* 48 8b 4a 08          mov    0x8(%rdx),%rcx <-- trapping instruction
>>    2e: f6 c1 01              test   $0x1,%cl
>>    31: 0f 85 cb 00 00 00    jne    0x102
>>    37: 0f 1f 44 00 00        nopl   0x0(%rax,%rax,1)
>>    3c: 31 c9                xor    %ecx,%ecx
>>    3e: 48                    rex.W
>>    3f: f7                    .byte 0xf7
>>
>> Code starting with the faulting instruction
>> ===========================================
>>     0: 48 8b 4a 08          mov    0x8(%rdx),%rcx
>>     4: f6 c1 01              test   $0x1,%cl
>>     7: 0f 85 cb 00 00 00    jne    0xd8
>>     d: 0f 1f 44 00 00        nopl   0x0(%rax,%rax,1)
>>    12: 31 c9                xor    %ecx,%ecx
>>    14: 48                    rex.W
>>    15: f7                    .byte 0xf7
>> [  991.201691] RSP: 0018:ffffb11281d0ba90 EFLAGS: 00010202
>> [  991.206910] RAX: ffffe14ec4208000 RBX: 0000000000005000 RCX: 0000000000000009
>> [  991.214033] RDX: 0000000000000000 RSI: 0000000000000006 RDI: 0000000000001000
>> [  991.221156] RBP: ffffb11281d0bb88 R08: 00000000000020ff R09: ffffe14ec4208000
>> [  991.228280] R10: 0000000000000005 R11: 0000000000000006 R12: ffff96b4825f4200
>> [  991.235406] R13: 0000000000000001 R14: 000000003d6277bf R15: 0000000000000000
>> [  991.242529] FS:  00007f41e80b9740(0000) GS:ffff96b83bc1b000(0000)
>> knlGS:0000000000000000
>> [  991.250608] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> [  991.256378] CR2: 0000000000000008 CR3: 0000000106c42003 CR4: 00000000003706f0
>> [  991.263513] Call Trace:
>> [  991.265956]  <TASK>
>> [  991.268055] __zerocopy_sg_from_iter (net/core/datagram.c:?)
>> [  991.272674] ? kmalloc_reserve (net/core/skbuff.c:581)
>> [  991.276599] skb_zerocopy_iter_stream (net/core/skbuff.c:1867)
>> [  991.281219] tcp_sendmsg_locked (net/ipv4/tcp.c:1283)
>> [  991.285493] tcp_sendmsg (net/ipv4/tcp.c:1393)
>> [  991.288896] inet6_sendmsg (net/ipv6/af_inet6.c:661)
>> [  991.292466] __sock_sendmsg (net/socket.c:717)
>> [  991.296126] __sys_sendto (net/socket.c:?)
>> [  991.299785] __x64_sys_sendto (net/socket.c:2235 net/socket.c:2231
>> net/socket.c:2231)
>> [  991.303622] x64_sys_call (arch/x86/entry/syscall_64.c:41)
>> [  991.307462] do_syscall_64 (arch/x86/entry/syscall_64.c:?)
>> [  991.311128] ? irqentry_exit (kernel/entry/common.c:210)
>> [  991.314881] ? exc_page_fault (arch/x86/mm/fault.c:1536)
>> [  991.318720] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)
>> [  991.323762] RIP: 0033:0x7f41e814b687
>> [ 991.327352] Code: 48 89 fa 4c 89 df e8 58 b3 00 00 8b 93 08 03 00 00
>> 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10
>> 0f 05 <5b> c3 0f 1f 80 00 00 00 00 83 e2 39 83 fa 08 75 de e8 23 ff ff
>> ff
>> All code
>> ========
>>     0: 48 89 fa              mov    %rdi,%rdx
>>     3: 4c 89 df              mov    %r11,%rdi
>>     6: e8 58 b3 00 00        call   0xb363
>>     b: 8b 93 08 03 00 00    mov    0x308(%rbx),%edx
>>    11: 59                    pop    %rcx
>>    12: 5e                    pop    %rsi
>>    13: 48 83 f8 fc          cmp    $0xfffffffffffffffc,%rax
>>    17: 74 1a                je     0x33
>>    19: 5b                    pop    %rbx
>>    1a: c3                    ret
>>    1b: 0f 1f 84 00 00 00 00 nopl   0x0(%rax,%rax,1)
>>    22: 00
>>    23: 48 8b 44 24 10        mov    0x10(%rsp),%rax
>>    28: 0f 05                syscall
>>    2a:* 5b                    pop    %rbx <-- trapping instruction
>>    2b: c3                    ret
>>    2c: 0f 1f 80 00 00 00 00 nopl   0x0(%rax)
>>    33: 83 e2 39              and    $0x39,%edx
>>    36: 83 fa 08              cmp    $0x8,%edx
>>    39: 75 de                jne    0x19
>>    3b: e8 23 ff ff ff        call   0xffffffffffffff63
>>
>> Code starting with the faulting instruction
>> ===========================================
>>     0: 5b                    pop    %rbx
>>     1: c3                    ret
>>     2: 0f 1f 80 00 00 00 00 nopl   0x0(%rax)
>>     9: 83 e2 39              and    $0x39,%edx
>>     c: 83 fa 08              cmp    $0x8,%edx
>>     f: 75 de                jne    0xffffffffffffffef
>>    11: e8 23 ff ff ff        call   0xffffffffffffff39
>> [  991.346124] RSP: 002b:00007ffdd843ba50 EFLAGS: 00000202 ORIG_RAX:
>> 000000000000002c
>> [  991.353680] RAX: ffffffffffffffda RBX: 00007f41e80b9740 RCX: 00007f41e814b687
>> [  991.360806] RDX: 000000000000f180 RSI: 000056251f1fd100 RDI: 0000000000000005
>> [  991.367931] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
>> [  991.375063] R10: 0000000004000000 R11: 0000000000000202 R12: 0000000000000000
>> [  991.382193] R13: 000056251f1fb080 R14: 000001a670e438d8 R15: 0000000000000005
>> [  991.389357]  </TASK>
>> [  991.391571] Modules linked in: mptcp_diag tcp_diag inet_diag
>> xt_conntrack xfrm_user ipip bridge stp llc geneve vxlan act_csum
>> act_pedit openvswitch nsh nf_nat nf_conntrack nf_defrag_ipv6
>> nf_defrag_ipv4 psample cls_flower sch_prio xt_mark nft_compat
>> nf_tables sch_ingress act_mirred cls_basic sch_fq_codel vrf pktgen
>> macvtap macvlan tap x86_pkg_temp_thermal ip_tables x_tables [last
>> unloaded: test_bpf]
>> [  991.426812] CR2: 0000000000000008
>> [  991.430121] ---[ end trace 0000000000000000 ]---
>> [  991.434733] RIP: 0010:zerocopy_fill_skb_from_iter
>> (include/linux/page-flags.h:284)
>> [ 991.440477] Code: 4d 85 c0 0f 84 04 01 00 00 44 39 c7 41 0f 4d f8 4c
>> 63 de 4a 8b 54 dc 30 49 89 d6 4d 29 ce 49 c1 fe 06 49 d3 ee 4d 85 f6
>> 74 24 <48> 8b 4a 08 f6 c1 01 0f 85 cb 00 00 00 0f 1f 44 00 00 31 c9 48
>> f7
>> All code
>> ========
>>     0: 4d 85 c0              test   %r8,%r8
>>     3: 0f 84 04 01 00 00    je     0x10d
>>     9: 44 39 c7              cmp    %r8d,%edi
>>     c: 41 0f 4d f8          cmovge %r8d,%edi
>>    10: 4c 63 de              movslq %esi,%r11
>>    13: 4a 8b 54 dc 30        mov    0x30(%rsp,%r11,8),%rdx
>>    18: 49 89 d6              mov    %rdx,%r14
>>    1b: 4d 29 ce              sub    %r9,%r14
>>    1e: 49 c1 fe 06          sar    $0x6,%r14
>>    22: 49 d3 ee              shr    %cl,%r14
>>    25: 4d 85 f6              test   %r14,%r14
>>    28: 74 24                je     0x4e
>>    2a:* 48 8b 4a 08          mov    0x8(%rdx),%rcx <-- trapping instruction
>>    2e: f6 c1 01              test   $0x1,%cl
>>    31: 0f 85 cb 00 00 00    jne    0x102
>>    37: 0f 1f 44 00 00        nopl   0x0(%rax,%rax,1)
>>    3c: 31 c9                xor    %ecx,%ecx
>>    3e: 48                    rex.W
>>    3f: f7                    .byte 0xf7
>>
>> Code starting with the faulting instruction
>> ===========================================
>>     0: 48 8b 4a 08          mov    0x8(%rdx),%rcx
>>     4: f6 c1 01              test   $0x1,%cl
>>     7: 0f 85 cb 00 00 00    jne    0xd8
>>     d: 0f 1f 44 00 00        nopl   0x0(%rax,%rax,1)
>>    12: 31 c9                xor    %ecx,%ecx
>>    14: 48                    rex.W
>>    15: f7                    .byte 0xf7
>> [  991.459215] RSP: 0018:ffffb11281d0ba90 EFLAGS: 00010202
>> [  991.464434] RAX: ffffe14ec4208000 RBX: 0000000000005000 RCX: 0000000000000009
>> [  991.471557] RDX: 0000000000000000 RSI: 0000000000000006 RDI: 0000000000001000
>> [  991.478681] RBP: ffffb11281d0bb88 R08: 00000000000020ff R09: ffffe14ec4208000
>> [  991.485807] R10: 0000000000000005 R11: 0000000000000006 R12: ffff96b4825f4200
>> [  991.492930] R13: 0000000000000001 R14: 000000003d6277bf R15: 0000000000000000
>> [  991.500054] FS:  00007f41e80b9740(0000) GS:ffff96b83bc1b000(0000)
>> knlGS:0000000000000000
>> [  991.508132] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> [  991.513870] CR2: 0000000000000008 CR3: 0000000106c42003 CR4: 00000000003706f0
>> [  991.520994] note: udpgso_bench_tx[64842] exited with irqs disabled
>>
>>
>> ## Source
>> * Kernel version: 6.17.0-rc4
>> * Git tree: https://kernel.googlesource.com/pub/scm/linux/kernel/git/next/linux-next.git
>> * Git describe: next-20250905
>> * Git commit: be5d4872e528796df9d7425f2bd9b3893eb3a42c
>> * Architectures: x86_64
>> * Toolchains: clang-nightly
>> * Kconfigs: defconfig+selftests/*/config
>>
>> ## Build
>> * Test log: https://qa-reports.linaro.org/api/testruns/29777495/log_file/
>> * LAVA test log: https://lkft.validation.linaro.org/scheduler/job/8434053#L16943
>> * Test details:
>> https://regressions.linaro.org/lkft/linux-next-master/next-20250905/log-parser-test/oops-oops-oops-smp-pti/
>> * Test plan: https://tuxapi.tuxsuite.com/v1/groups/linaro/projects/lkft/tests/32GkXBGNRNDEj5d64zd73eXhXQC
>> * Build link: https://storage.tuxsuite.com/public/linaro/lkft/builds/32GkU7mdlpISpPeeeEwIfAJuzqG/
>> * Kernel config:
>> https://storage.tuxsuite.com/public/linaro/lkft/builds/32GkU7mdlpISpPeeeEwIfAJuzqG/config
>>
>> --
>> Linaro LKFT
>> https://lkft.linaro.org
> 
> I suspect a bug added in mm/gup.c recently
> 
> commit db076b5db550aa34169dceee81d0974c7b2a2482
> Author: David Hildenbrand <david@...hat.com>
> Date:   Mon Sep 1 17:03:40 2025 +0200
> 
>      mm/gup: remove record_subpages()
> 
>      We can just cleanup the code by calculating the #refs earlier, so we can
>      just inline what remains of record_subpages().
> 
>      Calculate the number of references/pages ahead of times, and record them
>      only once all our tests passed.
> 
>      Link: https://lkml.kernel.org/r/20250901150359.867252-20-david@redhat.com
>      Signed-off-by: David Hildenbrand <david@...hat.com>
>      Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> 

Yes, fix already on its way:

https://lkml.kernel.org/r/5090355d-546a-4d06-99e1-064354d156b5@redhat.com

-- 
Cheers

David / dhildenb


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