[syzbot] KASAN: slab-out-of-bounds Read in copy_data

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 9ae1fbdeabd3 Add linux-next specific files for 20211025
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1331363cb00000
kernel config: https://syzkaller.appspot.com/x/.config?x=aeb17e42bc109064
dashboard link: https://syzkaller.appspot.com/bug?extid=b86736b5935e0d25b446
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=116ce954b00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=132fcf62b00000

The issue was bisected to:

commit 22849b5ea5952d853547cc5e0651f34a246b2a4f
Author: Leon Romanovsky <leo...@nvidia.com>
Date: Thu Oct 21 14:16:14 2021 +0000

devlink: Remove not-executed trap policer notifications

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=137d8bfcb00000
final oops: https://syzkaller.appspot.com/x/report.txt?x=10fd8bfcb00000
console output: https://syzkaller.appspot.com/x/log.txt?x=177d8bfcb00000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b86736...@syzkaller.appspotmail.com
Fixes: 22849b5ea595 ("devlink: Remove not-executed trap policer notifications")

==================================================================
BUG: KASAN: slab-out-of-bounds in memcpy include/linux/fortify-string.h:225 [inline]
BUG: KASAN: slab-out-of-bounds in copy_data+0xf3/0x2e0 drivers/char/hw_random/virtio-rng.c:68
Read of size 64 at addr ffff88801a7a1580 by task syz-executor989/6542

CPU: 1 PID: 6542 Comm: syz-executor989 Not tainted 5.15.0-rc6-next-20211025-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
print_address_description.constprop.0.cold+0x8d/0x320 mm/kasan/report.c:247
__kasan_report mm/kasan/report.c:433 [inline]
kasan_report.cold+0x83/0xdf mm/kasan/report.c:450
check_region_inline mm/kasan/generic.c:183 [inline]
kasan_check_range+0x13d/0x180 mm/kasan/generic.c:189
memcpy+0x20/0x60 mm/kasan/shadow.c:65
memcpy include/linux/fortify-string.h:225 [inline]
copy_data+0xf3/0x2e0 drivers/char/hw_random/virtio-rng.c:68
virtio_read+0x1e0/0x230 drivers/char/hw_random/virtio-rng.c:90
rng_get_data drivers/char/hw_random/core.c:192 [inline]
rng_dev_read+0x400/0x660 drivers/char/hw_random/core.c:229
vfs_read+0x1b5/0x600 fs/read_write.c:483
ksys_read+0x12d/0x250 fs/read_write.c:623
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7f05696617e9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 e1 14 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 c4 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffd06461948 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 000000000001294d RCX: 00007f05696617e9
RDX: 00000000fffffff1 RSI: 0000000020000180 RDI: 0000000000000003
RBP: 0000000000000000 R08: 00007ffd064619b0 R09: 00007ffd064619b0
R10: 00007ffd064613d0 R11: 0000000000000246 R12: 00007ffd0646197c
R13: 00007ffd064619b0 R14: 00007ffd06461990 R15: 0000000000000002
</TASK>

Allocated by task 1:
kasan_save_stack+0x1e/0x50 mm/kasan/common.c:38
kasan_set_track mm/kasan/common.c:46 [inline]
set_alloc_info mm/kasan/common.c:434 [inline]
____kasan_kmalloc mm/kasan/common.c:513 [inline]
____kasan_kmalloc mm/kasan/common.c:472 [inline]
__kasan_kmalloc+0xa9/0xd0 mm/kasan/common.c:522
kmalloc include/linux/slab.h:590 [inline]
kzalloc include/linux/slab.h:724 [inline]
probe_common+0xaa/0x5b0 drivers/char/hw_random/virtio-rng.c:132
virtio_dev_probe+0x44e/0x760 drivers/virtio/virtio.c:273
call_driver_probe drivers/base/dd.c:517 [inline]
really_probe+0x245/0xcc0 drivers/base/dd.c:596
__driver_probe_device+0x338/0x4d0 drivers/base/dd.c:751
driver_probe_device+0x4c/0x1a0 drivers/base/dd.c:781
__driver_attach+0x22d/0x4e0 drivers/base/dd.c:1140
bus_for_each_dev+0x147/0x1d0 drivers/base/bus.c:301
bus_add_driver+0x41d/0x630 drivers/base/bus.c:618
driver_register+0x220/0x3a0 drivers/base/driver.c:171
do_one_initcall+0x103/0x650 init/main.c:1303
do_initcall_level init/main.c:1378 [inline]
do_initcalls init/main.c:1394 [inline]
do_basic_setup init/main.c:1413 [inline]
kernel_init_freeable+0x6b1/0x73a init/main.c:1618
kernel_init+0x1a/0x1d0 init/main.c:1507
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

The buggy address belongs to the object at ffff88801a7a1400
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 384 bytes inside of
512-byte region [ffff88801a7a1400, ffff88801a7a1600)
The buggy address belongs to the page:
page:ffffea000069e800 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1a7a0
head:ffffea000069e800 order:2 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 dead000000000100 dead000000000122 ffff888010c41c80
raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 2, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 1, ts 7709676886, free_ts 0
prep_new_page mm/page_alloc.c:2418 [inline]
get_page_from_freelist+0xa72/0x2f50 mm/page_alloc.c:4149
__alloc_pages+0x1b2/0x500 mm/page_alloc.c:5369
alloc_page_interleave+0x1e/0x200 mm/mempolicy.c:2036
alloc_pages+0x29f/0x300 mm/mempolicy.c:2186
alloc_slab_page mm/slub.c:1793 [inline]
allocate_slab mm/slub.c:1930 [inline]
new_slab+0x32d/0x4a0 mm/slub.c:1993
___slab_alloc+0x918/0xfe0 mm/slub.c:3022
__slab_alloc.constprop.0+0x4d/0xa0 mm/slub.c:3109
slab_alloc_node mm/slub.c:3200 [inline]
slab_alloc mm/slub.c:3242 [inline]
kmem_cache_alloc_trace+0x289/0x2c0 mm/slub.c:3259
kmalloc include/linux/slab.h:590 [inline]
kzalloc include/linux/slab.h:724 [inline]
device_private_init drivers/base/core.c:3238 [inline]
device_add+0x11a7/0x1ee0 drivers/base/core.c:3288
device_create_groups_vargs+0x203/0x280 drivers/base/core.c:4052
device_create_with_groups+0xe3/0x120 drivers/base/core.c:4138
misc_register+0x20a/0x690 drivers/char/misc.c:206
register_miscdev drivers/char/hw_random/core.c:422 [inline]
hwrng_modinit+0xd0/0x109 drivers/char/hw_random/core.c:621
do_one_initcall+0x103/0x650 init/main.c:1303
do_initcall_level init/main.c:1378 [inline]
do_initcalls init/main.c:1394 [inline]
do_basic_setup init/main.c:1413 [inline]
kernel_init_freeable+0x6b1/0x73a init/main.c:1618
kernel_init+0x1a/0x1d0 init/main.c:1507
page_owner free stack trace missing

Memory state around the buggy address:
ffff88801a7a1480: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff88801a7a1500: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff88801a7a1580: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff88801a7a1600: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88801a7a1680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
For information about bisection process see: https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this issue, for details see:
https://goo.gl/tpsmEJ#testing-patches

[Eric Dumazet]

On 10/26/21 9:39 AM, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 9ae1fbdeabd3 Add linux-next specific files for 20211025
> git tree: linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=1331363cb00000
> kernel config: https://syzkaller.appspot.com/x/.config?x=aeb17e42bc109064
> dashboard link: https://syzkaller.appspot.com/bug?extid=b86736b5935e0d25b446
> compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=116ce954b00000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=132fcf62b00000
>
> The issue was bisected to:
>
> commit 22849b5ea5952d853547cc5e0651f34a246b2a4f
> Author: Leon Romanovsky <leo...@nvidia.com>
> Date: Thu Oct 21 14:16:14 2021 +0000
>
> devlink: Remove not-executed trap policer notifications

More likely this came with

caaf2874ba27b92bca6f0298bf88bad94067ec37 hwrng: virtio - don't waste entropy

[Laurent Vivier]

On 27/10/2021 00:34, Eric Dumazet wrote:
>
>
> On 10/26/21 9:39 AM, syzbot wrote:
>> Hello,
>>
>> syzbot found the following issue on:
>>
>> HEAD commit: 9ae1fbdeabd3 Add linux-next specific files for 20211025
>> git tree: linux-next
>> console output: https://syzkaller.appspot.com/x/log.txt?x=1331363cb00000
>> kernel config: https://syzkaller.appspot.com/x/.config?x=aeb17e42bc109064
>> dashboard link: https://syzkaller.appspot.com/bug?extid=b86736b5935e0d25b446
>> compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=116ce954b00000
>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=132fcf62b00000
>>
>> The issue was bisected to:
>>
>> commit 22849b5ea5952d853547cc5e0651f34a246b2a4f
>> Author: Leon Romanovsky <leo...@nvidia.com>
>> Date: Thu Oct 21 14:16:14 2021 +0000
>>
>> devlink: Remove not-executed trap policer notifications
>
> More likely this came with
>
> caaf2874ba27b92bca6f0298bf88bad94067ec37 hwrng: virtio - don't waste entropy
>

I'm going to have a look.

Thanks,
Laurent

[Michael S. Tsirkin]

How bad is it if we just drop this and waste some bytes of entropy?

--
MST

[Laurent Vivier]

I don't think it's bad at all. In most of the cases we should use the full buffer.

So, you can drop, I will re-submit them later with a fix.

Thanks,
Laurent

[Laurent Vivier]

I'm not able to reproduce the problem with next-20211026 and the C reproducer.

And reviewing the code in copy_data() I don't see any issue.

Is it possible to know what it the VM configuration used to test it?

Thanks,
Laurent

[syzbot]

Hello,

syzbot tried to test the proposed patch but the build/boot failed:

failed to checkout kernel repo g...@github.com:vivier/linux.git/virtio-rng: failed to run ["git" "fetch" "--force" "03a2ad2d258fa835dfab9af4663cf25f84ccba11" "virtio-rng"]: exit status 128
Host key verification failed.
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.



Tested on:

commit: [unknown
git tree: g...@github.com:vivier/linux.git virtio-rng

[Dmitry Vyukov]

Hi Laurent,

syzbot used e2-standard-2 GCE VM when that happened.
You can see some info about these VMs under the "VM info" link on the dashboard.

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KASAN: slab-out-of-bounds Read in copy_data

==================================================================
BUG: KASAN: slab-out-of-bounds in memcpy include/linux/fortify-string.h:191 [inline]

BUG: KASAN: slab-out-of-bounds in copy_data+0xf3/0x2e0 drivers/char/hw_random/virtio-rng.c:68

Read of size 64 at addr ffff88801a9f7180 by task syz-executor.1/9327

CPU: 1 PID: 9327 Comm: syz-executor.1 Not tainted 5.15.0-rc7-syzkaller #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:

__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106

print_address_description.constprop.0.cold+0x6c/0x309 mm/kasan/report.c:256
__kasan_report mm/kasan/report.c:442 [inline]
kasan_report.cold+0x83/0xdf mm/kasan/report.c:459

check_region_inline mm/kasan/generic.c:183 [inline]
kasan_check_range+0x13d/0x180 mm/kasan/generic.c:189
memcpy+0x20/0x60 mm/kasan/shadow.c:65

memcpy include/linux/fortify-string.h:191 [inline]

copy_data+0xf3/0x2e0 drivers/char/hw_random/virtio-rng.c:68
virtio_read+0x1e0/0x230 drivers/char/hw_random/virtio-rng.c:90
rng_get_data drivers/char/hw_random/core.c:192 [inline]
rng_dev_read+0x400/0x660 drivers/char/hw_random/core.c:229
vfs_read+0x1b5/0x600 fs/read_write.c:483
ksys_read+0x12d/0x250 fs/read_write.c:623
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae

RIP: 0033:0x7fe7032b7a39
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fe702a2d188 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 00007fe7033baf60 RCX: 00007fe7032b7a39

RDX: 00000000fffffff1 RSI: 0000000020000180 RDI: 0000000000000003

RBP: 00007fe703311e8f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffce85cce5f R14: 00007fe702a2d300 R15: 0000000000022000

Allocated by task 1:
kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38

kasan_set_track mm/kasan/common.c:46 [inline]
set_alloc_info mm/kasan/common.c:434 [inline]
____kasan_kmalloc mm/kasan/common.c:513 [inline]
____kasan_kmalloc mm/kasan/common.c:472 [inline]

__kasan_kmalloc+0xa4/0xd0 mm/kasan/common.c:522
kmalloc include/linux/slab.h:591 [inline]
kzalloc include/linux/slab.h:721 [inline]
probe_common+0xaa/0x5b0 drivers/char/hw_random/virtio-rng.c:132
virtio_dev_probe+0x44e/0x6f0 drivers/virtio/virtio.c:273

call_driver_probe drivers/base/dd.c:517 [inline]
really_probe+0x245/0xcc0 drivers/base/dd.c:596
__driver_probe_device+0x338/0x4d0 drivers/base/dd.c:751
driver_probe_device+0x4c/0x1a0 drivers/base/dd.c:781
__driver_attach+0x22d/0x4e0 drivers/base/dd.c:1140
bus_for_each_dev+0x147/0x1d0 drivers/base/bus.c:301

bus_add_driver+0x3a9/0x630 drivers/base/bus.c:618
driver_register+0x220/0x3a0 drivers/base/driver.c:171
do_one_initcall+0x103/0x650 init/main.c:1304
do_initcall_level init/main.c:1377 [inline]
do_initcalls init/main.c:1393 [inline]
do_basic_setup init/main.c:1412 [inline]
kernel_init_freeable+0x6b1/0x73a init/main.c:1615
kernel_init+0x1a/0x1d0 init/main.c:1506
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

The buggy address belongs to the object at ffff88801a9f7000

which belongs to the cache kmalloc-512 of size 512
The buggy address is located 384 bytes inside of

512-byte region [ffff88801a9f7000, ffff88801a9f7200)

The buggy address belongs to the page:

page:ffffea00006a7d00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1a9f4
head:ffffea00006a7d00 order:2 compound_mapcount:0 compound_pincount:0

flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 dead000000000100 dead000000000122 ffff888010c41c80
raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated

page last allocated via order 2, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 1, ts 7611196546, free_ts 0
prep_new_page mm/page_alloc.c:2424 [inline]
get_page_from_freelist+0xa72/0x2f80 mm/page_alloc.c:4153
__alloc_pages+0x1b2/0x500 mm/page_alloc.c:5375

alloc_page_interleave+0x1e/0x200 mm/mempolicy.c:2036
alloc_pages+0x29f/0x300 mm/mempolicy.c:2186

alloc_slab_page mm/slub.c:1770 [inline]
allocate_slab mm/slub.c:1907 [inline]
new_slab+0x319/0x490 mm/slub.c:1970
___slab_alloc+0x950/0x1050 mm/slub.c:3001
__slab_alloc.constprop.0+0x4d/0xa0 mm/slub.c:3088
slab_alloc_node mm/slub.c:3179 [inline]
slab_alloc mm/slub.c:3221 [inline]
kmem_cache_alloc_trace+0x302/0x3c0 mm/slub.c:3238
kmalloc include/linux/slab.h:591 [inline]
kzalloc include/linux/slab.h:721 [inline]
device_private_init drivers/base/core.c:3240 [inline]
device_add+0x11a7/0x1ee0 drivers/base/core.c:3290
tty_register_device_attr+0x395/0x7b0 drivers/tty/tty_io.c:3285
tty_port_register_device_attr_serdev+0x109/0x140 drivers/tty/tty_port.c:168
uart_add_one_port+0xbaa/0x11c0 drivers/tty/serial/serial_core.c:2914
serial8250_register_8250_port+0x120f/0x1cc0 drivers/tty/serial/8250/8250_core.c:1083
serial_pnp_probe+0x4a4/0x850 drivers/tty/serial/8250/8250_pnp.c:482
pnp_device_probe+0x29d/0x4b0 drivers/pnp/driver.c:111

call_driver_probe drivers/base/dd.c:517 [inline]
really_probe+0x245/0xcc0 drivers/base/dd.c:596

page_owner free stack trace missing

Memory state around the buggy address:

ffff88801a9f7080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff88801a9f7100: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff88801a9f7180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff88801a9f7200: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88801a9f7280: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


Tested on:

commit: e7457c35 hwrng: virtio - always add a pending request
git tree: https://github.com/vivier/linux.git virtio-rng
console output: https://syzkaller.appspot.com/x/log.txt?x=1596699ab00000
kernel config: https://syzkaller.appspot.com/x/.config?x=abd68735072d9e5f

[Michael S. Tsirkin]

Could you pls confirm whether reverting
caaf2874ba27b92bca6f0298bf88bad94067ec37 addresses this?

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-and-tested-by: syzbot+b86736...@syzkaller.appspotmail.com

Tested on:

commit: d721abbe hwrng: virtio - don't wait on cleanup
git tree: https://github.com/vivier/linux.git
kernel config: https://syzkaller.appspot.com/x/.config?x=abd68735072d9e5f

dashboard link: https://syzkaller.appspot.com/bug?extid=b86736b5935e0d25b446
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2

Note: testing is done by a robot and is best-effort only.

[Laurent Vivier]

I've restarted the syzbot on top of "hwrng: virtio - don't wait on cleanup" [1] and the
problem has not been triggered.

See https://syzkaller.appspot.com/bug?extid=b86736b5935e0d25b446

Thanks,
Laurent

[1]
d721abbeb145 hwrng: virtio - don't wait on cleanup
bb768beb0a5f hwrng: virtio - add an internal buffer
d25f27432f80 (origin/master, origin/HEAD, master) Merge tag 'arm-soc-fixes-5.15-3' of
git://git.kernel.org/pub/scm/linux/kernel/git/soc/soc

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-and-tested-by: syzbot+b86736...@syzkaller.appspotmail.com

Tested on:

commit: 162d68d0 hwrng: virtio - don't waste entropy

git tree: https://github.com/vivier/linux.git
kernel config: https://syzkaller.appspot.com/x/.config?x=abd68735072d9e5f

dashboard link: https://syzkaller.appspot.com/bug?extid=b86736b5935e0d25b446
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2

[Laurent Vivier]

The problem seems to be introduced by the last patch:

"hwrng: virtio - always add a pending request"

not

"hwrng: virtio - don't waste entropy"

Thanks,
Laurent

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-and-tested-by: syzbot+b86736...@syzkaller.appspotmail.com

Tested on:

commit: 563762a8 fix

git tree: https://github.com/vivier/linux.git virtio-rng

kernel config: https://syzkaller.appspot.com/x/.config?x=abd68735072d9e5f

dashboard link: https://syzkaller.appspot.com/bug?extid=b86736b5935e0d25b446
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2

[Laurent Vivier]

I think I understand the problem.

As we check data_avail != 0 before waiting on the completion, we can have a data_idx != 0.

The following change fixes the problem for me:

--- a/drivers/char/hw_random/virtio-rng.c
+++ b/drivers/char/hw_random/virtio-rng.c
@@ -52,6 +52,8 @@ static void request_entropy(struct virtrng_info *vi)
struct scatterlist sg;

reinit_completion(&vi->have_data);
+ vi->data_avail = 0;
+ vi->data_idx = 0;

sg_init_one(&sg, vi->data, sizeof(vi->data));


MST, do you update the patch or do you want I send a new version?

Thanks,
Laurent

[Michael S. Tsirkin]

New version of the patchset pls, and note in the changelog
that just this patch changed.

--
MST

[syzbot]

Auto-closing this bug as obsolete.
No recent activity, existing reproducers are no longer triggering the issue.