Re: [QUESTION] WARNNING after 3d8e2128f26a ("sysfs: Add sysfs_emit and sysfs_emit_at to format sysfs output")

[yangerkun <yangerkun@huawei.com>]

Emm...

Actually, the problem exist for stable branch like 4.19 after fix for 
CVE-2021-27365 which include the follow two patch:
2efc459d06f1 ("sysfs: Add sysfs_emit and sysfs_emit_at to format sysfs 
output")
ec98ea7070e9 ("scsi: iscsi: Ensure sysfs attributes are limited to 
PAGE_SIZE")


在 2021/4/2 15:16, yangerkun 写道:
> sysfs_emit(3d8e2128f26a ("sysfs: Add sysfs_emit and sysfs_emit_at to
> format sysfs output")) has a hidden constraint that the buf should be
> alignment with PAGE_SIZE. It's OK since 59bb47985c1d ("mm, sl[aou]b:
> guarantee natural alignment for kmalloc(power-of-two)") help us to solve
> scenes like CONFIG_SLUB_DEBUG or CONFIG_SLOB which will break this.
> 
> 
> But since lots of stable branch(we reproduce it with 4.19 stable) merge
> 3d8e2128f26a ("sysfs: Add sysfs_emit and sysfs_emit_at to format sysfs
> output") without 59bb47985c1d ("mm, sl[aou]b: guarantee natural
> alignment for kmalloc(power-of-two)"), we will get the follow warning
> with command 'cat /sys/class/iscsi_transport/tcp/handle' once we enable
> CONFIG_SLUB_DEBUG and start kernel with slub_debug=UFPZ!
> 
> 
> Obviously, we can backport 59bb47985c1d ("mm, sl[aou]b: guarantee
> natural alignment for kmalloc(power-of-two)") to fix it. But this will
> waste some memory to ensure natural alignment which seems unbearable for
> embedded device. So for stable branch like 4.19, can we just remove the
> warning in sysfs_emit since the only user for it is iscsi, and seq_read
> + sysfs_kf_seq_show can ensure that the buf in sysfs_emit must be aware
> of PAGE_SIZE. Or does there some other advise for this problem?
> 
> 
> # without 59bb47985c1d + 1G ram
> [root@localhost ~]# free
>                total        used        free      shared  buff/cache
> available
> Mem:         947336      169960      389732         896      387644
> 624216
> Swap:             0           0           0
> 
> # merge with 59bb47985c1d + 1G ram
> [root@localhost ~]# free
>                total        used        free      shared  buff/cache
> available
> Mem:         947340      175176      374396         896      397768
> 618964
> Swap:             0           0           0
> [root@localhost ~]#
> 
> 
> [   37.683332] ------------[ cut here ]------------
> [   37.692747] invalid sysfs_emit: buf:00000000f75441ab
> [   37.693914] WARNING: CPU: 1 PID: 576 at fs/sysfs/file.c:577 
> sysfs_emit+0xb9/0xe0
> [   37.694861] Modules linked in:
> [   37.695264] CPU: 1 PID: 576 Comm: cat Not tainted 
> 4.19.183-00023-gdf225d326e8c #7
> [   37.696210] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), 
> BIOS ?-20190727_073836-buildvm-ppc64le-16.ppc.fedoraproject.org-3.fc31 
> 04/01/2014
> [   37.697866] RIP: 0010:sysfs_emit+0xb9/0xe0
> [   37.698387] Code: 47 c9 c3 48 83 05 76 33 b3 04 01 48 89 fe 48 c7 c7 
> 64 08 bb 8a 48 83 05 7c 33 b3 04 01 e8 13 7f be 00 48 83 05 77 33 b3 04 
> 01 <0f> 0b 48 83 05 75 33 b3 04 01 48 83 05 73
> [   37.700713] RSP: 0018:ffffc90000af7cf8 EFLAGS: 00010202
> [   37.701370] RAX: 0000000000000000 RBX: ffff88803e0e4c00 RCX: 
> 0000000000000006
> [   37.702261] RDX: 0000000000000007 RSI: 0000000000000006 RDI: 
> ffff888039455bf0
> [   37.703171] RBP: ffffc90000af7d48 R08: 00000000000002f8 R09: 
> 0000000000000005
> [   37.704079] R10: 00000000000002f7 R11: ffffffff8bd9534d R12: 
> ffff88801a013740
> [   37.705001] R13: ffff88803db37a08 R14: ffff88803db37a30 R15: 
> ffff88803db37a48
> [   37.705918] FS:  00007fcb96411580(0000) GS:ffff888039440000(0000) 
> knlGS:0000000000000000
> [   37.706956] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   37.707692] CR2: 00007fcb88cf0000 CR3: 000000001a501000 CR4: 
> 00000000000006e0
> [   37.708607] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 
> 0000000000000000
> [   37.709520] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 
> 0000000000000400
> [   37.710427] Call Trace:
> [   37.710784]  show_transport_handle+0x3e/0x60
> [   37.711338]  dev_attr_show+0x22/0x60
> [   37.711808]  sysfs_kf_seq_show+0xc6/0x190
> [   37.712332]  kernfs_seq_show+0x25/0x30
> [   37.712862]  seq_read+0xe1/0x540
> [   37.713292]  ? __handle_mm_fault+0xba3/0x1c70
> [   37.713866]  kernfs_fop_read+0x36/0x230
> [   37.714371]  __vfs_read+0x3c/0x230
> [   37.714819]  ? handle_mm_fault+0x1d1/0x340
> [   37.715345]  vfs_read+0xb5/0x1b0
> [   37.715774]  ksys_read+0x67/0x130
> [   37.716218]  __x64_sys_read+0x1e/0x30
> [   37.716701]  do_syscall_64+0x95/0x3d0
> [   37.717175]  ? do_async_page_fault+0x2e/0x190
> [   37.717747]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> [   37.718406] RIP: 0033:0x7fcb963363f2
> [   37.718881] Code: c0 e9 b2 fe ff ff 50 48 8d 3d 8a 41 0a 00 e8 75 f0 
> 01 00 0f 1f 44 00 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 0f 
> 05 <48> 3d 00 f0 ff ff 77 56 c3 0f 1f 44 00 04
> [   37.721290] RSP: 002b:00007ffea78dff18 EFLAGS: 00000246 ORIG_RAX: 
> 0000000000000000
> [   37.722264] RAX: ffffffffffffffda RBX: 0000000000020000 RCX: 
> 00007fcb963363f2
> [   37.723169] RDX: 0000000000020000 RSI: 00007fcb88cf1000 RDI: 
> 0000000000000003
> [   37.724100] RBP: 00007fcb88cf1000 R08: 00007fcb88cf0010 R09: 
> 0000000000000000
> [   37.725039] R10: 0000000000000022 R11: 0000000000000246 R12: 
> 0000000000020f00
> [   37.725945] R13: 0000000000000003 R14: 0000000000020000 R15: 
> 0000000000020000
> [   37.726857] ---[ end trace fbd5b85cd7d85530 ]---
> 
> .