Fail to fuzz with latest Syzkaller

[Harshit Mogalapalli]

Hello,

With the latest upstream(defconfig + KASAN/KCOV + kvm_guest.config) and latest syzkaller my local fuzzing instance continues to get these errors.

Linux Kernel:

# git describe
v6.18-rc7-13-g30f09200cc4a
# git log
commit 30f09200cc4aefbd8385b01e41bde2e4565a6f0e (HEAD -> master, origin/master, origin/HEAD)

Syzkaller:

# git log
commit 64219f1537429ca826770c4d6f3d49ee6964d16c (HEAD -> master, origin/master, origin/HEAD)

SYZFAIL: mmap of data segment failed want 0x200000000000, got 0xffffffffffffffff (errno 13: Permission denied) 

SYZFAIL: mmap of data segment failed want 0x200000000000, got 0xffffffffffffffff (errno 13: Permission denied) 

Thanks,

Harshit

[Harshit Mogalapalli]

Looks like this is fixed when I disable CONFIG_SECURITY_SELINUX :) 

Can't reporuce those errors anymore after disabling the above config which gets enabled by default. I think we might have to document it ?

Thanks,

Harshit

Thanks,

Harshit

[Aleksandr Nogikh]

Do you also observe the same problems if you use syzbot's selinux config?
https://raw.githubusercontent.com/google/syzkaller/refs/heads/master/dashboard/config/linux/upstream-selinux-kasan.config

>
> Thanks,
> Harshit
>
> Thanks,
> Harshit
>
>
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[Harshit Mogalapalli]

On Wednesday, 26 November 2025 at 22:44:06 UTC+5:30 nog...@google.com wrote:

On Wed, Nov 26, 2025 at 5:41 PM Harshit Mogalapalli
<harshit.m....@gmail.com> wrote:
>
>
>
> On Wednesday, 26 November 2025 at 20:24:24 UTC+5:30 Harshit Mogalapalli wrote:
>
> Hello,
>
> With the latest upstream(defconfig + KASAN/KCOV + kvm_guest.config) and latest syzkaller my local fuzzing instance continues to get these errors.
>
> Linux Kernel:
> # git describe
> v6.18-rc7-13-g30f09200cc4a
> # git log
> commit 30f09200cc4aefbd8385b01e41bde2e4565a6f0e (HEAD -> master, origin/master, origin/HEAD)
>
> Syzkaller:
> # git log
> commit 64219f1537429ca826770c4d6f3d49ee6964d16c (HEAD -> master, origin/master, origin/HEAD)
>
> SYZFAIL: mmap of data segment failed want 0x200000000000, got 0xffffffffffffffff (errno 13: Permission denied)
> SYZFAIL: mmap of data segment failed want 0x200000000000, got 0xffffffffffffffff (errno 13: Permission denied)
>
>
> Looks like this is fixed when I disable CONFIG_SECURITY_SELINUX :)
>
> Can't reporuce those errors anymore after disabling the above config which gets enabled by default. I think we might have to document it ?

Do you also observe the same problems if you use syzbot's selinux config?
https://raw.githubusercontent.com/google/syzkaller/refs/heads/master/dashboard/config/linux/upstream-selinux-kasan.config

Yep, I just tried it and I could reproduce it:

2025/11/26 18:25:08 VM 2: crash(tail14): SYZFAIL: mmap of data segment failed
2025/11/26 18:25:08 VM 2: crash(tail15): SYZFAIL: mmap of data segment failed
2025/11/26 18:25:08 VM 2: crash(tail16): SYZFAIL: mmap of data segment failed
2025/11/26 18:25:08 VM 2: crash(tail17): SYZFAIL: mmap of data segment failed
2025/11/26 18:25:08 VM 2: crash(tail18): SYZFAIL: mmap of data segment failed
2025/11/26 18:25:0

Thanks,

Harshit 

[Harshit Mogalapalli]

And disabling CONFIG_SECURITY_SELINUX solves it. (so upstream-kasan-selinux config also needs fixing I think ?)

Also I am using the -hda image generated using " https://raw.githubusercontent.com/google/syzkaller/master/tools/create-image.sh "

[Dmitry Vyukov]

It may be that Selinux policy in the latest images prohibits
PROT_WRITE|PROT_EXEC mappings. You may disable that bit of the policy
if you want to test with Selinux.

On Thu, 27 Nov 2025 at 05:16, Harshit Mogalapalli

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