syzbot

map[ReproOpts:{
	"procs": 1,
	"type": "none",
	"repeat": true
} ReproSyz:mkdir(&(0x7f0000000000)='./mnt\x00', 0x1ed)
syz_mount_image(&(0x7f0000000100)='ext4\x00', 0x0, &(0x7f0000000000)='./mnt\x00', 0x0, 0x0, 0x0, &(0x7f0000000200)='')
r0 = open(&(0x7f0000001000)='/sys/fs/ext4/loop0/stripe\x00', 0x1, 0x0)
write(r0, &(0x7f0000002000)='131072\x00', 0x6)
close(r0)
r1 = open(&(0x7f0000001100)='/sys/fs/ext4/loop1/stripe\x00', 0x1, 0x0)
write(r1, &(0x7f0000002000)='131072\x00', 0x6)
close(r1)
r2 = open(&(0x7f0000001200)='/sys/fs/ext4/loop2/stripe\x00', 0x1, 0x0)
write(r2, &(0x7f0000002000)='131072\x00', 0x6)
close(r2)
r3 = open(&(0x7f0000001300)='/sys/fs/ext4/loop3/stripe\x00', 0x1, 0x0)
write(r3, &(0x7f0000002000)='131072\x00', 0x6)
close(r3)
r4 = open(&(0x7f0000001400)='/sys/fs/ext4/loop4/stripe\x00', 0x1, 0x0)
write(r4, &(0x7f0000002000)='131072\x00', 0x6)
close(r4)
r5 = open(&(0x7f0000003000)='./mnt/file0\x00', 0x42, 0x1ff)
pwrite64(r5, &(0x7f0000004000)='a', 0x1, 0x8000c61)
 SyzkallerCommit:31e9c887f7dc24e04b3ca70d0d54fc34141844b0]

map[DescriptionFiles:[acpi_thermal_rel.txt aio.txt auto.txt binfmt.txt bpf.txt bpf_prog.txt bpf_trace.txt cgroup.txt damon.txt dev_ashmem.txt dev_bifrost.txt dev_binder.txt dev_binderfs.txt dev_block.txt dev_bsg.txt dev_bus_usb.txt dev_camx.txt dev_cdrom.txt dev_cec.txt dev_char_usb.txt dev_comedi.txt dev_dma_heap.txt dev_dri.txt dev_dsp.txt dev_dvb_demux.txt dev_dvb_dvr.txt dev_dvb_frontend.txt dev_fb.txt dev_floppy.txt dev_hidraw.txt dev_i2c.txt dev_i915.txt dev_img_rogue.txt dev_infiniband_rdma.txt dev_infiniband_rdma_cm.txt dev_input.txt dev_iommu.txt dev_kvm.txt dev_kvm_amd64.txt dev_kvm_arm64.txt dev_kvm_extra.txt dev_kvm_riscv64.txt dev_loop.txt dev_mali.txt dev_media.txt dev_msm.txt dev_msr.txt dev_nbd.txt dev_net_tun.txt dev_panthor.txt dev_ppp.txt dev_ptmx.txt dev_ptp.txt dev_qat_adf_ctl.txt dev_qrtr_tun.txt dev_random.txt dev_rfkill.txt dev_rtc.txt dev_sequencer.txt dev_sg.txt dev_snapshot.txt dev_snd_control.txt dev_snd_hw.txt dev_snd_midi.txt dev_snd_pcm.txt dev_snd_seq.txt dev_snd_timer.txt dev_sr.txt dev_sw_sync.txt dev_tlk_device.txt dev_trusty.txt dev_udmabuf.txt dev_uhid.txt dev_uinput.txt dev_usb_hiddev.txt dev_usbmon.txt dev_userio.txt dev_vfio.txt dev_vga_arbiter.txt dev_vhci.txt dev_video4linux.txt dev_video4linux_vim2m.txt dev_virtual_nci.txt dev_vtpm.txt fanotify.txt filesystem.txt fs_9p.txt fs_fuse.txt fs_incfs.txt fs_ioctl.txt fs_ioctl_autofs.txt fs_ioctl_btrfs.txt fs_ioctl_ext4.txt fs_ioctl_f2fs.txt fs_ioctl_fat.txt fs_ioctl_fscrypt.txt fs_ioctl_fsverity.txt fs_ioctl_xfs.txt futex.txt hafnium.txt inotify.txt io_uring.txt ipc.txt key.txt kfuzztest.txt l2cap.txt landlock.txt lsm.txt namespaces.txt net_80211.txt netfilter.txt netfilter_arp.txt netfilter_bridge.txt netfilter_ipv4.txt netfilter_ipv6.txt netfilter_ipvs.txt netfilter_targets.txt pagemap_ioctl.txt perf.txt prctl.txt quotactl.txt seccomp.txt security_apparmor.txt security_selinux.txt security_smack.txt socket.txt socket_alg.txt socket_ax25.txt socket_bluetooth.txt socket_caif.txt socket_can.txt socket_ieee802154.txt socket_inet.txt socket_inet6.txt socket_inet_dccp.txt socket_inet_icmp.txt socket_inet_igmp.txt socket_inet_l2tp.txt socket_inet_sctp.txt socket_inet_tcp.txt socket_inet_udp.txt socket_ip_tunnel.txt socket_isdn.txt socket_kcm.txt socket_key.txt socket_llc.txt socket_netlink.txt socket_netlink_audit.txt socket_netlink_crypto.txt socket_netlink_generic.txt socket_netlink_generic_80211.txt socket_netlink_generic_batadv.txt socket_netlink_generic_devlink.txt socket_netlink_generic_ethtool.txt socket_netlink_generic_fou.txt socket_netlink_generic_gtp.txt socket_netlink_generic_mptcp.txt socket_netlink_generic_net_dm.txt socket_netlink_generic_netlabel.txt socket_netlink_generic_nfc.txt socket_netlink_generic_seg6.txt socket_netlink_generic_smc.txt socket_netlink_generic_team.txt socket_netlink_generic_wireguard.txt socket_netlink_netfilter.txt socket_netlink_netfilter_acct.txt socket_netlink_netfilter_conntrack.txt socket_netlink_netfilter_conntrack_exp.txt socket_netlink_netfilter_conntrack_helper.txt socket_netlink_netfilter_ipset.txt socket_netlink_netfilter_log.txt socket_netlink_netfilter_nft_compat.txt socket_netlink_netfilter_nftables.txt socket_netlink_netfilter_osf.txt socket_netlink_netfilter_queue.txt socket_netlink_netfilter_timeout.txt socket_netlink_rdma.txt socket_netlink_route.txt socket_netlink_route_sched.txt socket_netlink_route_sched_retired.txt socket_netlink_sock_diag.txt socket_netlink_xfrm.txt socket_netrom.txt socket_nfc.txt socket_nvme_of_tcp.txt socket_packet.txt socket_phonet.txt socket_pppox.txt socket_qipcrtr.txt socket_rds.txt socket_rose.txt socket_rxrpc.txt socket_tipc.txt socket_tipc_netlink.txt socket_unix.txt socket_vnet.txt socket_x25.txt socket_xdp.txt sys.txt uffd.txt usbip.txt vmw_vmci.txt vnet.txt vnet_mptcp.txt vusb.txt watch_queue.txt xattr.txt] SyzkallerCommit:31e9c887f7dc24e04b3ca70d0d54fc34141844b0]

map[KernelSrc:/usr/local/google/home/dvyukov/syzkaller/agent/workdir/cache/src/15b4f5eb70de38f0af710cd4f5da9d3c4be8a9f5]

map[KernelObj:/usr/local/google/home/dvyukov/syzkaller/agent/workdir/cache/build/e91c906f0ba3f45e7289dd533f45ea1306dab031]

gemini-3-pro-preview

map[ReproOpts:{
	"procs": 1,
	"type": "none",
	"repeat": true
}]

You are an expert in linux kernel fuzzing. Your goal is to write a syzkaller program to trigger a specific bug.
Print only the syz program that could be executed directly, without backticks.




Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.

Bug Title: kernel BUG in ext4_mb_normalize_request

Original Crash Report:
EXT4-fs (loop2): start 0, size 131072, fe_logical 131072
------------[ cut here ]------------
kernel BUG at fs/ext4/mballoc.c:4657!
Oops: invalid opcode: 0000 [#1] SMP KASAN PTI
CPU: 1 UID: 0 PID: 6131 Comm: syz.2.37 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:ext4_mb_normalize_request+0x1cd8/0x1d10 fs/ext4/mballoc.c:4657
Code: 71 ae ff 48 8b 44 24 38 48 8b 38 48 c7 c6 80 bc fe 8a 48 c7 c2 e0 d2 fe 8a 48 8b 4c 24 28 4d 89 f0 49 89 d9 e8 19 f5 09 00 90 <0f> 0b e8 f1 3a 4c ff 90 0f 0b e8 e9 3a 4c ff 90 0f 0b e8 e1 3a 4c
RSP: 0018:ffffc9000613ed20 EFLAGS: 00010246
RAX: f56237077cb2d800 RBX: 0000000000020000 RCX: f56237077cb2d800
RDX: ffffc9000ff71000 RSI: 0000000000000674 RDI: 0000000000000675
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: fffff52000c27d2d R12: ffffffff00020800
R13: dffffc0000000000 R14: 0000000000020000 R15: 0000000000020000
FS:  00007f17dd9456c0(0000) GS:ffff888126def000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000110f246add CR3: 000000002897a000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 ext4_mb_new_blocks+0xc46/0x46b0 fs/ext4/mballoc.c:6310
 ext4_ext_map_blocks+0x1877/0x69c0 fs/ext4/extents.c:4383
 ext4_map_create_blocks fs/ext4/inode.c:613 [inline]
 ext4_map_blocks+0x82c/0x16f0 fs/ext4/inode.c:816
 _ext4_get_block+0x1fa/0x4c0 fs/ext4/inode.c:916
 ext4_block_write_begin+0xb03/0x1940 fs/ext4/inode.c:1203
 ext4_write_begin+0xb3a/0x1870 fs/ext4/ext4_jbd2.h:-1
 ext4_da_write_begin+0x352/0xd30 fs/ext4/inode.c:3130
 generic_perform_write+0x29d/0x8c0 mm/filemap.c:4314
 ext4_buffered_write_iter+0xd0/0x3a0 fs/ext4/file.c:299
 ext4_file_write_iter+0x293/0x1be0 fs/ext4/file.c:-1
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x5d5/0xb40 fs/read_write.c:686
 ksys_pwrite64 fs/read_write.c:793 [inline]
 __do_sys_pwrite64 fs/read_write.c:801 [inline]
 __se_sys_pwrite64 fs/read_write.c:798 [inline]
 __x64_sys_pwrite64+0x196/0x220 fs/read_write.c:798
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xec/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f17df6ff749
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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f17dd945038 EFLAGS: 00000246 ORIG_RAX: 0000000000000012
RAX: ffffffffffffffda RBX: 00007f17df956090 RCX: 00007f17df6ff749
RDX: 0000000000000001 RSI: 0000200000000140 RDI: 0000000000000008
RBP: 00007f17df783f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000008000c61 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f17df956128 R14: 00007f17df956090 R15: 00007ffdca7c0738
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:ext4_mb_normalize_request+0x1cd8/0x1d10 fs/ext4/mballoc.c:4657
Code: 71 ae ff 48 8b 44 24 38 48 8b 38 48 c7 c6 80 bc fe 8a 48 c7 c2 e0 d2 fe 8a 48 8b 4c 24 28 4d 89 f0 49 89 d9 e8 19 f5 09 00 90 <0f> 0b e8 f1 3a 4c ff 90 0f 0b e8 e9 3a 4c ff 90 0f 0b e8 e1 3a 4c
RSP: 0018:ffffc9000613ed20 EFLAGS: 00010246
RAX: f56237077cb2d800 RBX: 0000000000020000 RCX: f56237077cb2d800
RDX: ffffc9000ff71000 RSI: 0000000000000674 RDI: 0000000000000675
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: fffff52000c27d2d R12: ffffffff00020800
R13: dffffc0000000000 R14: 0000000000020000 R15: 0000000000020000
FS:  00007f17dd9456c0(0000) GS:ffff888126def000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000110f246add CR3: 000000002897a000 CR4: 00000000003526f0


The list of existing description files:
acpi_thermal_rel.txt
aio.txt
auto.txt
binfmt.txt
bpf.txt
bpf_prog.txt
bpf_trace.txt
cgroup.txt
damon.txt
dev_ashmem.txt
dev_bifrost.txt
dev_binder.txt
dev_binderfs.txt
dev_block.txt
dev_bsg.txt
dev_bus_usb.txt
dev_camx.txt
dev_cdrom.txt
dev_cec.txt
dev_char_usb.txt
dev_comedi.txt
dev_dma_heap.txt
dev_dri.txt
dev_dsp.txt
dev_dvb_demux.txt
dev_dvb_dvr.txt
dev_dvb_frontend.txt
dev_fb.txt
dev_floppy.txt
dev_hidraw.txt
dev_i2c.txt
dev_i915.txt
dev_img_rogue.txt
dev_infiniband_rdma.txt
dev_infiniband_rdma_cm.txt
dev_input.txt
dev_iommu.txt
dev_kvm.txt
dev_kvm_amd64.txt
dev_kvm_arm64.txt
dev_kvm_extra.txt
dev_kvm_riscv64.txt
dev_loop.txt
dev_mali.txt
dev_media.txt
dev_msm.txt
dev_msr.txt
dev_nbd.txt
dev_net_tun.txt
dev_panthor.txt
dev_ppp.txt
dev_ptmx.txt
dev_ptp.txt
dev_qat_adf_ctl.txt
dev_qrtr_tun.txt
dev_random.txt
dev_rfkill.txt
dev_rtc.txt
dev_sequencer.txt
dev_sg.txt
dev_snapshot.txt
dev_snd_control.txt
dev_snd_hw.txt
dev_snd_midi.txt
dev_snd_pcm.txt
dev_snd_seq.txt
dev_snd_timer.txt
dev_sr.txt
dev_sw_sync.txt
dev_tlk_device.txt
dev_trusty.txt
dev_udmabuf.txt
dev_uhid.txt
dev_uinput.txt
dev_usb_hiddev.txt
dev_usbmon.txt
dev_userio.txt
dev_vfio.txt
dev_vga_arbiter.txt
dev_vhci.txt
dev_video4linux.txt
dev_video4linux_vim2m.txt
dev_virtual_nci.txt
dev_vtpm.txt
fanotify.txt
filesystem.txt
fs_9p.txt
fs_fuse.txt
fs_incfs.txt
fs_ioctl.txt
fs_ioctl_autofs.txt
fs_ioctl_btrfs.txt
fs_ioctl_ext4.txt
fs_ioctl_f2fs.txt
fs_ioctl_fat.txt
fs_ioctl_fscrypt.txt
fs_ioctl_fsverity.txt
fs_ioctl_xfs.txt
futex.txt
hafnium.txt
inotify.txt
io_uring.txt
ipc.txt
key.txt
kfuzztest.txt
l2cap.txt
landlock.txt
lsm.txt
namespaces.txt
net_80211.txt
netfilter.txt
netfilter_arp.txt
netfilter_bridge.txt
netfilter_ipv4.txt
netfilter_ipv6.txt
netfilter_ipvs.txt
netfilter_targets.txt
pagemap_ioctl.txt
perf.txt
prctl.txt
quotactl.txt
seccomp.txt
security_apparmor.txt
security_selinux.txt
security_smack.txt
socket.txt
socket_alg.txt
socket_ax25.txt
socket_bluetooth.txt
socket_caif.txt
socket_can.txt
socket_ieee802154.txt
socket_inet.txt
socket_inet6.txt
socket_inet_dccp.txt
socket_inet_icmp.txt
socket_inet_igmp.txt
socket_inet_l2tp.txt
socket_inet_sctp.txt
socket_inet_tcp.txt
socket_inet_udp.txt
socket_ip_tunnel.txt
socket_isdn.txt
socket_kcm.txt
socket_key.txt
socket_llc.txt
socket_netlink.txt
socket_netlink_audit.txt
socket_netlink_crypto.txt
socket_netlink_generic.txt
socket_netlink_generic_80211.txt
socket_netlink_generic_batadv.txt
socket_netlink_generic_devlink.txt
socket_netlink_generic_ethtool.txt
socket_netlink_generic_fou.txt
socket_netlink_generic_gtp.txt
socket_netlink_generic_mptcp.txt
socket_netlink_generic_net_dm.txt
socket_netlink_generic_netlabel.txt
socket_netlink_generic_nfc.txt
socket_netlink_generic_seg6.txt
socket_netlink_generic_smc.txt
socket_netlink_generic_team.txt
socket_netlink_generic_wireguard.txt
socket_netlink_netfilter.txt
socket_netlink_netfilter_acct.txt
socket_netlink_netfilter_conntrack.txt
socket_netlink_netfilter_conntrack_exp.txt
socket_netlink_netfilter_conntrack_helper.txt
socket_netlink_netfilter_ipset.txt
socket_netlink_netfilter_log.txt
socket_netlink_netfilter_nft_compat.txt
socket_netlink_netfilter_nftables.txt
socket_netlink_netfilter_osf.txt
socket_netlink_netfilter_queue.txt
socket_netlink_netfilter_timeout.txt
socket_netlink_rdma.txt
socket_netlink_route.txt
socket_netlink_route_sched.txt
socket_netlink_route_sched_retired.txt
socket_netlink_sock_diag.txt
socket_netlink_xfrm.txt
socket_netrom.txt
socket_nfc.txt
socket_nvme_of_tcp.txt
socket_packet.txt
socket_phonet.txt
socket_pppox.txt
socket_qipcrtr.txt
socket_rds.txt
socket_rose.txt
socket_rxrpc.txt
socket_tipc.txt
socket_tipc_netlink.txt
socket_unix.txt
socket_vnet.txt
socket_x25.txt
socket_xdp.txt
sys.txt
uffd.txt
usbip.txt
vmw_vmci.txt
vnet.txt
vnet_mptcp.txt
vusb.txt
watch_queue.txt
xattr.txt

mkdir(&(0x7f0000000000)='./mnt\x00', 0x1ed)
syz_mount_image(&(0x7f0000000100)='ext4\x00', 0x0, &(0x7f0000000000)='./mnt\x00', 0x0, 0x0, 0x0, &(0x7f0000000200)='')
r0 = open(&(0x7f0000001000)='/sys/fs/ext4/loop0/stripe\x00', 0x1, 0x0)
write(r0, &(0x7f0000002000)='131072\x00', 0x6)
close(r0)
r1 = open(&(0x7f0000001100)='/sys/fs/ext4/loop1/stripe\x00', 0x1, 0x0)
write(r1, &(0x7f0000002000)='131072\x00', 0x6)
close(r1)
r2 = open(&(0x7f0000001200)='/sys/fs/ext4/loop2/stripe\x00', 0x1, 0x0)
write(r2, &(0x7f0000002000)='131072\x00', 0x6)
close(r2)
r3 = open(&(0x7f0000001300)='/sys/fs/ext4/loop3/stripe\x00', 0x1, 0x0)
write(r3, &(0x7f0000002000)='131072\x00', 0x6)
close(r3)
r4 = open(&(0x7f0000001400)='/sys/fs/ext4/loop4/stripe\x00', 0x1, 0x0)
write(r4, &(0x7f0000002000)='131072\x00', 0x6)
close(r4)
r5 = open(&(0x7f0000003000)='./mnt/file0\x00', 0x42, 0x1ff)
pwrite64(r5, &(0x7f0000004000)='a', 0x1, 0x8000c61)

gemini-3-pro-preview

							input: 4584
							output: 43
							thoughts: 19698
						

**Fulfilling the Syzkaller Request: Triggering an ext4 Kernel BUG**

Alright, let's break this down. The objective is clear: generate a Syzkaller program to trigger a kernel BUG within `ext4_mb_normalize_request`. The core issue, as indicated by the crash report, revolves around a `BUG_ON` assertion within this function, specifically concerning block allocation during an `ext4` write operation, in particular, `pwrite64`.

The crash signature points to a scenario where a write, probably with delayed allocation, is happening.  The `ext4_mb_normalize_request` function is critical here. Its job is to manage the requested block allocation, and it appears there's some sort of inconsistency related to either the requested parameters (offset, size) or the filesystem state.  The log's `start 0, size 131072, fe_logical 131072` offers an essential clue, particularly the unusual "size" value. This implies a power-of-2 allocation with a size of 128MB (assuming 1KB blocks).

Looking at the code, particularly line 4657 in `mballoc.c`, it seems the bug might be caused by an assertion related to the normalized request exceeding some limits. There's a critical check in the function that asserts `start + size <= ac->ac_o_ex.fe_logical && start > ac->ac_o_ex.fe_logical;`.  This check seems flawed, comparing the normalized starting block with the original, and could be the crux of the issue.

The strategy hinges on reproducing this specific state. I'll need to create an `ext4` image, mount it, open a file, and then perform a write in such a way that the allocation behavior triggers this `BUG_ON`. A `pwrite64` operation with delayed allocation is key. The provided offset and size values strongly hint that block size is 1KB.

The crash report tells me that I need to provide an `ext4` image and control the filesystem's behavior. I can use `syz_mount_image` to achieve this. However, to produce a specific size, I need to craft the image with either large files or modify filesystem settings. My initial thoughts are that if I can set the block size to 1KB, that will help with reproduction. However, I can also force the bug by providing an image where the `s_raid_stripe_width` field is set to a large number.  This, in turn, will cause `ext4_mb_normalize_request` to normalize the size to an overly large value.  I also recall that some kernels may not have size validation, and the bug may not be present when the validation is implemented.

Given the constraints, manipulating `s_raid_stripe_width` looks to be a good target. While I can't construct an image with a specific block size directly using `syz_mount_image`, sysfs can provide a backdoor:  I can use a standard `ext4` image and then write to `/sys/fs/ext4/loopX/stripe` to set the stripe size, bypassing any superblock checks on setting the stripe size.

By writing 131072 to the stripe sysfs entry, I'm forcing alignment to that value, and the subsequent write operation should cause `ext4_mb_normalize_request` to calculate an extremely large size, triggering the `BUG_ON` due to the size calculation. The code to achieve this would involve mounting an image, writing to the sysfs entry, then performing a small write at a large offset, reproducing the behavior reported in the crash report. Specifically: mount, sysfs write, and `pwrite64`.  The sysfs write bypasses the check to only use a valid stripe size.  I am leveraging the lack of sanity checks within sysfs and exploiting the alignment calculation. The `size` variable becomes 131072. Since the code doesn't limit it, the BUG is hit. The bug is thus triggered. I just constructed the Syzkaller reproducer.

map[ReproOpts:{
	"procs": 1,
	"type": "none",
	"repeat": true
}]

map[ReproOpts:{
	"procs": 1,
	"type": "none",
	"repeat": true
}]

gemini-3-pro-preview

							input: 25257
							output: 674
							thoughts: 0