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    Subject[PATCH 4.9 18/57] blktrace: Fix uaf in blk_trace access after removing by sysfs
    Date
    From: Zhihao Cheng <chengzhihao1@huawei.com>

    [ Upstream commit 5afedf670caf30a2b5a52da96eb7eac7dee6a9c9 ]

    There is an use-after-free problem triggered by following process:

    P1(sda) P2(sdb)
    echo 0 > /sys/block/sdb/trace/enable
    blk_trace_remove_queue
    synchronize_rcu
    blk_trace_free
    relay_close
    rcu_read_lock
    __blk_add_trace
    trace_note_tsk
    (Iterate running_trace_list)
    relay_close_buf
    relay_destroy_buf
    kfree(buf)
    trace_note(sdb's bt)
    relay_reserve
    buf->offset <- nullptr deference (use-after-free) !!!
    rcu_read_unlock

    [ 502.714379] BUG: kernel NULL pointer dereference, address:
    0000000000000010
    [ 502.715260] #PF: supervisor read access in kernel mode
    [ 502.715903] #PF: error_code(0x0000) - not-present page
    [ 502.716546] PGD 103984067 P4D 103984067 PUD 17592b067 PMD 0
    [ 502.717252] Oops: 0000 [#1] SMP
    [ 502.720308] RIP: 0010:trace_note.isra.0+0x86/0x360
    [ 502.732872] Call Trace:
    [ 502.733193] __blk_add_trace.cold+0x137/0x1a3
    [ 502.733734] blk_add_trace_rq+0x7b/0xd0
    [ 502.734207] blk_add_trace_rq_issue+0x54/0xa0
    [ 502.734755] blk_mq_start_request+0xde/0x1b0
    [ 502.735287] scsi_queue_rq+0x528/0x1140
    ...
    [ 502.742704] sg_new_write.isra.0+0x16e/0x3e0
    [ 502.747501] sg_ioctl+0x466/0x1100

    Reproduce method:
    ioctl(/dev/sda, BLKTRACESETUP, blk_user_trace_setup[buf_size=127])
    ioctl(/dev/sda, BLKTRACESTART)
    ioctl(/dev/sdb, BLKTRACESETUP, blk_user_trace_setup[buf_size=127])
    ioctl(/dev/sdb, BLKTRACESTART)

    echo 0 > /sys/block/sdb/trace/enable &
    // Add delay(mdelay/msleep) before kernel enters blk_trace_free()

    ioctl$SG_IO(/dev/sda, SG_IO, ...)
    // Enters trace_note_tsk() after blk_trace_free() returned
    // Use mdelay in rcu region rather than msleep(which may schedule out)

    Remove blk_trace from running_list before calling blk_trace_free() by
    sysfs if blk_trace is at Blktrace_running state.

    Fixes: c71a896154119f ("blktrace: add ftrace plugin")
    Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
    Link: https://lore.kernel.org/r/20210923134921.109194-1-chengzhihao1@huawei.com
    Signed-off-by: Jens Axboe <axboe@kernel.dk>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    kernel/trace/blktrace.c | 8 ++++++++
    1 file changed, 8 insertions(+)

    diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
    index 88eb9261c7b5..056107787f4a 100644
    --- a/kernel/trace/blktrace.c
    +++ b/kernel/trace/blktrace.c
    @@ -1584,6 +1584,14 @@ static int blk_trace_remove_queue(struct request_queue *q)
    if (bt == NULL)
    return -EINVAL;

    + if (bt->trace_state == Blktrace_running) {
    + bt->trace_state = Blktrace_stopped;
    + spin_lock_irq(&running_trace_lock);
    + list_del_init(&bt->running_list);
    + spin_unlock_irq(&running_trace_lock);
    + relay_flush(bt->rchan);
    + }
    +
    put_probe_ref();
    synchronize_rcu();
    blk_trace_free(bt);
    --
    2.33.0


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