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SubjectRe: [PATCH] erofs: fix pcluster use-after-free on UP platforms
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On 2022/9/2 12:57, Gao Xiang wrote:
> During stress testing with CONFIG_SMP disabled, KASAN reports as below:
>
> ==================================================================
> BUG: KASAN: use-after-free in __mutex_lock+0xe5/0xc30
> Read of size 8 at addr ffff8881094223f8 by task stress/7789
> [ 3482.258885]
> CPU: 0 PID: 7789 Comm: stress Not tainted 6.0.0-rc1-00002-g0d53d2e882f9 #3
> Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
> Call Trace:
> <TASK>
> ..
> __mutex_lock+0xe5/0xc30
> ..
> z_erofs_do_read_page+0x8ce/0x1560
> ..
> z_erofs_readahead+0x31c/0x580
> ..
> Freed by task 7787
> kasan_save_stack+0x1e/0x40
> kasan_set_track+0x20/0x30
> kasan_set_free_info+0x20/0x40
> __kasan_slab_free+0x10c/0x190
> kmem_cache_free+0xed/0x380
> rcu_core+0x3d5/0xc90
> __do_softirq+0x12d/0x389
> [ 3482.295630]
> Last potentially related work creation:
> kasan_save_stack+0x1e/0x40
> __kasan_record_aux_stack+0x97/0xb0
> call_rcu+0x3d/0x3f0
> erofs_shrink_workstation+0x11f/0x210
> erofs_shrink_scan+0xdc/0x170
> shrink_slab.constprop.0+0x296/0x530
> drop_slab+0x1c/0x70
> drop_caches_sysctl_handler+0x70/0x80
> proc_sys_call_handler+0x20a/0x2f0
> vfs_write+0x555/0x6c0
> ksys_write+0xbe/0x160
> do_syscall_64+0x3b/0x90
>
> The root cause is that erofs_workgroup_unfreeze() doesn't reset
> to orig_val thus it causes a race that the pcluster reuses unexpectedly
> before freeing.
>
> Since UP platforms are quite rare now, such path becomes unnecessary.
> Let's drop such specific-designed path directly instead.
>
> Fixes: 73f5c66df3e2 ("staging: erofs: fix `erofs_workgroup_{try_to_freeze, unfreeze}'")
> Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

Reviewed-by: Chao Yu <chao@kernel.org>

Thanks,

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