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    Subject[PATCH 5.19 134/192] erofs: fix pcluster use-after-free on UP platforms
    Date
    From: Gao Xiang <hsiangkao@linux.alibaba.com>

    [ Upstream commit 2f44013e39984c127c6efedf70e6b5f4e9dcf315 ]

    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

    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

    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}'")
    Reviewed-by: Yue Hu <huyue2@coolpad.com>
    Reviewed-by: Chao Yu <chao@kernel.org>
    Link: https://lore.kernel.org/r/20220902045710.109530-1-hsiangkao@linux.alibaba.com
    Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    fs/erofs/internal.h | 29 -----------------------------
    1 file changed, 29 deletions(-)

    diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
    index cfee49d33b95a..a01cc82795a25 100644
    --- a/fs/erofs/internal.h
    +++ b/fs/erofs/internal.h
    @@ -195,7 +195,6 @@ struct erofs_workgroup {
    atomic_t refcount;
    };

    -#if defined(CONFIG_SMP)
    static inline bool erofs_workgroup_try_to_freeze(struct erofs_workgroup *grp,
    int val)
    {
    @@ -224,34 +223,6 @@ static inline int erofs_wait_on_workgroup_freezed(struct erofs_workgroup *grp)
    return atomic_cond_read_relaxed(&grp->refcount,
    VAL != EROFS_LOCKED_MAGIC);
    }
    -#else
    -static inline bool erofs_workgroup_try_to_freeze(struct erofs_workgroup *grp,
    - int val)
    -{
    - preempt_disable();
    - /* no need to spin on UP platforms, let's just disable preemption. */
    - if (val != atomic_read(&grp->refcount)) {
    - preempt_enable();
    - return false;
    - }
    - return true;
    -}
    -
    -static inline void erofs_workgroup_unfreeze(struct erofs_workgroup *grp,
    - int orig_val)
    -{
    - preempt_enable();
    -}
    -
    -static inline int erofs_wait_on_workgroup_freezed(struct erofs_workgroup *grp)
    -{
    - int v = atomic_read(&grp->refcount);
    -
    - /* workgroup is never freezed on uniprocessor systems */
    - DBG_BUGON(v == EROFS_LOCKED_MAGIC);
    - return v;
    -}
    -#endif /* !CONFIG_SMP */
    #endif /* !CONFIG_EROFS_FS_ZIP */

    /* we strictly follow PAGE_SIZE and no buffer head yet */
    --
    2.35.1


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