[syzbot] [block?] memory leak in null_init_zoned_dev

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 06cf61899d64 Merge tag 'x86-urgent-2026-08-08' of git://gi..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=146d4149580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6843f8fd2336602d
dashboard link: https://syzkaller.appspot.com/bug?extid=f57d67a92532a98a562d
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=126d4149580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11531132580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/e023ff6ad9bc/disk-06cf6189.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ea49527ba5df/vmlinux-06cf6189.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e3d6468d0490/bzImage-06cf6189.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f57d67...@syzkaller.appspotmail.com

BUG: memory leak
unreferenced object 0xffff888126990000 (size 56000):
comm "syz.0.17", pid 5947, jiffies 4294943074
hex dump (first 32 bytes):
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 02 00 00 00 01 00 00 00 ................
backtrace (crc 5c9573f8):
___kmalloc_large_node+0xbc/0x100 mm/slub.c:5287
__kmalloc_large_node_noprof+0x1a/0xb0 mm/slub.c:5305
__do_kmalloc_node mm/slub.c:5322 [inline]
__kvmalloc_node_noprof+0x460/0x6f0 mm/slub.c:6905
null_init_zoned_dev+0x108/0x520 drivers/block/null_blk/zoned.c:94
null_add_dev+0x8a6/0xae0 drivers/block/null_blk/main.c:1993
nullb_device_power_store+0xf9/0x1f0 drivers/block/null_blk/main.c:501
flush_write_buffer fs/configfs/file.c:207 [inline]
configfs_write_iter+0x10d/0x1a0 fs/configfs/file.c:229
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x3ac/0x720 fs/read_write.c:687
ksys_write+0xa5/0x170 fs/read_write.c:739
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xf8/0x610 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

BUG: memory leak
unreferenced object 0xffff888127f80000 (size 56000):
comm "syz.0.18", pid 5951, jiffies 4294943093
hex dump (first 32 bytes):
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 02 00 00 00 01 00 00 00 ................
backtrace (crc 5c9573f8):
___kmalloc_large_node+0xbc/0x100 mm/slub.c:5287
__kmalloc_large_node_noprof+0x1a/0xb0 mm/slub.c:5305
__do_kmalloc_node mm/slub.c:5322 [inline]
__kvmalloc_node_noprof+0x460/0x6f0 mm/slub.c:6905
null_init_zoned_dev+0x108/0x520 drivers/block/null_blk/zoned.c:94
null_add_dev+0x8a6/0xae0 drivers/block/null_blk/main.c:1993
nullb_device_power_store+0xf9/0x1f0 drivers/block/null_blk/main.c:501
flush_write_buffer fs/configfs/file.c:207 [inline]
configfs_write_iter+0x10d/0x1a0 fs/configfs/file.c:229
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x3ac/0x720 fs/read_write.c:687
ksys_write+0xa5/0x170 fs/read_write.c:739
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xf8/0x610 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

connection error: failed to recv *flatrpc.ExecutorMessageRawT: EOF


---
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[Edward Adam Davis]

#syz test

diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
index f8c0fd57e041..fb001d002d17 100644
--- a/drivers/block/null_blk/main.c
+++ b/drivers/block/null_blk/main.c
@@ -511,6 +511,7 @@ static ssize_t nullb_device_power_store(struct config_item *item,
if (test_and_clear_bit(NULLB_DEV_FL_UP, &dev->flags)) {
dev->power = newp;
null_del_dev(dev->nullb);
+ null_free_zoned_dev(dev);
}
clear_bit(NULLB_DEV_FL_CONFIGURED, &dev->flags);
}

[syzbot]

Hello,

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

Reported-by: syzbot+f57d67...@syzkaller.appspotmail.com
Tested-by: syzbot+f57d67...@syzkaller.appspotmail.com

Tested on:

commit: 2f1baf1f Merge tag 'trace-v7.2-rc7' of git://git.kerne..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1096fac6580000

kernel config: https://syzkaller.appspot.com/x/.config?x=6843f8fd2336602d
dashboard link: https://syzkaller.appspot.com/bug?extid=f57d67a92532a98a562d
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44

patch: https://syzkaller.appspot.com/x/patch.diff?x=12ce0279580000

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

[Edward Adam Davis]

A user powers off the device by writing 0 to `./config/nullb/nullb1/power`
via the nullb configfs interface, and later powers it on by writing 1
to the same file.

When the power-off command is executed, the zones created by the previous
task are not freed before new zones are created upon powering on again;
this results in the memory leak described in [1].

Add an operation to free zones within nullb_device_power_store().

[1]

BUG: memory leak
unreferenced object 0xffff888126990000 (size 56000):

backtrace (crc 5c9573f8):

null_init_zoned_dev+0x108/0x520 drivers/block/null_blk/zoned.c:94
null_add_dev+0x8a6/0xae0 drivers/block/null_blk/main.c:1993
nullb_device_power_store+0xf9/0x1f0 drivers/block/null_blk/main.c:501
flush_write_buffer fs/configfs/file.c:207 [inline]
configfs_write_iter+0x10d/0x1a0 fs/configfs/file.c:229
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x3ac/0x720 fs/read_write.c:687

Fixes: cedcafad8277 ("nullb: add interface to power on disk")
Reported-by: syzbot+f57d67...@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=f57d67a92532a98a562d
Tested-by: syzbot+f57d67...@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <ead...@qq.com>
---
drivers/block/null_blk/main.c | 1 +
1 file changed, 1 insertion(+)

--
2.43.0