| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <CAGudoHHdFXeN4kRXxdBxV_fumQqxeTxjfFb2oSrvTxu-pC5u7g@mail.gmail.com>
Date: Wed, 7 Jan 2026 16:20:50 +0100
From: Mateusz Guzik <mjguzik@...il.com>
To: Breno Leitao <leitao@...ian.org>
Cc: Christian Brauner <brauner@...nel.org>, linux-kernel@...r.kernel.org,
viro@...iv.linux.org.uk, rostedt@...dmis.org, linux-fsdevel@...r.kernel.org,
kernel-team@...a.com
Subject: Re: [PATCH] device_cgroup: remove branch hint after code refactor
On Wed, Jan 7, 2026 at 4:17 PM Breno Leitao <leitao@...ian.org> wrote:
>
> Hello Mateusz,
>
> On Wed, Jan 07, 2026 at 03:17:40PM +0100, Mateusz Guzik wrote:
> > On Wed, Jan 7, 2026 at 3:06 PM Breno Leitao <leitao@...ian.org> wrote:
> > > diff --git a/include/linux/device_cgroup.h b/include/linux/device_cgroup.h
> > > index 0864773a57e8..822085bc2d20 100644
> > > --- a/include/linux/device_cgroup.h
> > > +++ b/include/linux/device_cgroup.h
> > > @@ -21,7 +21,7 @@ static inline int devcgroup_inode_permission(struct inode *inode, int mask)
> > > if (likely(!S_ISBLK(inode->i_mode) && !S_ISCHR(inode->i_mode)))
> > > return 0;
> > >
> > > - if (likely(!inode->i_rdev))
> > > + if (!inode->i_rdev)
> > > return 0;
> > >
> >
> > The branch was left there because I could not be bothered to analyze
> > whether it can be straight up eleminated with the new checks in place.
> >
> > A quick look at init_special_inode suggests it is an invariant rdev is
> > there in this case.
> >
> > So for the time being I would replace likely with WARN_ON_ONCE . Might
> > be even a good candidate for the pending release.
>
> Oh, in fact that was my first try, but, when I tested it, I found that
> it warns in some cases.
>
heh, bummer
in that case:
Reviewed-by: Mateusz Guzik <mjguzik@...il.com>
thanks
> [ 126.951410] WARNING: ./include/linux/device_cgroup.h:24 at inode_permission+0x181/0x190, CPU#4: networkd)/1212
> [ 126.971659] Modules linked in: intel_uncore_frequency(E) intel_uncore_frequency_common(E) skx_edac(E) skx_edac_common(E) nfit(E) libnvdimm(E) x86_pkg_temp_thermal(E) intel_powerclamp(E) coretemp(E) kvm_intel(E) kvm(E) iTCO_wdt(E) iTCO_vendor_support(E) irqbypass(E) acpi_cpufreq(E) i2c_i801(E) i2c_smbus(E) wmi(E) ipmi_si(E) ipmi_devintf(E) ipmi_msghandler(E) evdev(E) button(E) bpf_preload(E) sch_fq_codel(E) xhci_pci(E) xhci_hcd(E) vhost_net(E) tap(E) tun(E) vhost(E) vhost_iotlb(E) mpls_gso(E) mpls_iptunnel(E) mpls_router(E) fou(E) loop(E) efivarfs(E) autofs4(E)
> [ 127.097485] Tainted: [S]=CPU_OUT_OF_SPEC, [E]=UNSIGNED_MODULE
> [ 127.109038] Hardware name: Quanta Delta Lake MP 29F0EMA01D0/Delta Lake-Class1, BIOS F0E_3A21 06/27/2024
> [ 127.127889] RIP: 0010:inode_permission (./include/linux/device_cgroup.h:24 fs/namei.c:600)
> [ 127.137542] Code: 14 81 e2 ff ff 0f 00 31 ff 3d 00 60 00 00 41 8d 0c 48 40 0f 95 c7 ff c7 e8 5c 68 35 00 85 c0 0f 85 6d ff ff ff e9 29 ff ff ff <0f> 0b e9 22 ff ff ff 0f 1f 84 00 00 00 00 00 41 56 53 49 89 f6 48
> All code
> ========
> 0: 14 81 adc $0x81,%al
> 2: e2 ff loop 0x3
> 4: ff 0f decl (%rdi)
> 6: 00 31 add %dh,(%rcx)
> 8: ff (bad)
> 9: 3d 00 60 00 00 cmp $0x6000,%eax
> e: 41 8d 0c 48 lea (%r8,%rcx,2),%ecx
> 12: 40 0f 95 c7 setne %dil
> 16: ff c7 inc %edi
> 18: e8 5c 68 35 00 call 0x356879
> 1d: 85 c0 test %eax,%eax
> 1f: 0f 85 6d ff ff ff jne 0xffffffffffffff92
> 25: e9 29 ff ff ff jmp 0xffffffffffffff53
> 2a:* 0f 0b ud2 <-- trapping instruction
> 2c: e9 22 ff ff ff jmp 0xffffffffffffff53
> 31: 0f 1f 84 00 00 00 00 nopl 0x0(%rax,%rax,1)
> 38: 00
> 39: 41 56 push %r14
> 3b: 53 push %rbx
> 3c: 49 89 f6 mov %rsi,%r14
> 3f: 48 rex.W
>
> Code starting with the faulting instruction
> ===========================================
> 0: 0f 0b ud2
> 2: e9 22 ff ff ff jmp 0xffffffffffffff29
> 7: 0f 1f 84 00 00 00 00 nopl 0x0(%rax,%rax,1)
> e: 00
> f: 41 56 push %r14
> 11: 53 push %rbx
> 12: 49 89 f6 mov %rsi,%r14
> 15: 48 rex.W
> [ 127.175161] RSP: 0018:ffffc9000438fe60 EFLAGS: 00010246
> [ 127.185667] RAX: 0000000000002000 RBX: 0000000000000010 RCX: 0000000000006000
> [ 127.199992] RDX: 0000000000000000 RSI: ffff88842a9b5418 RDI: ffffffff83e31178
> [ 127.214320] RBP: 0000000000000001 R08: 0000000000000001 R09: 0000000000000000
> [ 127.228667] R10: 0000000000000000 R11: ffff88842a9b54b0 R12: ffffffff83e31178
> [ 127.243017] R13: ffff88842a9b5418 R14: ffff88842a9b5418 R15: ffff88842a9b5498
> [ 127.257360] FS: 00007f86e4bc3900(0000) GS:ffff8890b23fa000(0000) knlGS:0000000000000000
> [ 127.273624] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 127.285172] CR2: 000055990443e068 CR3: 00000004183b2001 CR4: 00000000007726f0
> [ 127.299500] PKRU: 55555554
> [ 127.304961] Call Trace:
> [ 127.309885] <TASK>
> [ 127.314121] do_faccessat (fs/open.c:508)
> [ 127.321488] ? entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:131)
> [ 127.331973] __x64_sys_access (fs/open.c:549 fs/open.c:547 fs/open.c:547)
> [ 127.339677] do_syscall_64 (arch/x86/entry/syscall_64.c:?)
> [ 127.347038] ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
> [ 127.354775] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:131)
> [ 127.364914] RIP: 0033:0x7f86e42ff21b
>
>
> Lines against commit f0b9d8eb98df ("Merge tag 'nfsd-6.19-3' of
> git://git.kernel.org/pub/scm/linux/kernel/git/cel/linux"), plus something like:
>
>
> diff --git a/include/linux/device_cgroup.h b/include/linux/device_cgroup.h
> index 822085bc2d20..c2b933a318f8 100644
> --- a/include/linux/device_cgroup.h
> +++ b/include/linux/device_cgroup.h
> @@ -21,7 +21,7 @@ static inline int devcgroup_inode_permission(struct inode *inode, int mask)
> if (likely(!S_ISBLK(inode->i_mode) && !S_ISCHR(inode->i_mode)))
> return 0;
>
> - if (likely(!inode->i_rdev))
> + if (WARN_ON_ONCE(!inode->i_rdev))
> return 0;
>
> if (S_ISBLK(inode->i_mode))
>
>
Powered by blists - more mailing lists