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Subject: Re: [PATCH] io_uring: Fix NULL pointer dereference in loop_rw_iter()
To:     Guoyu Huang <hgy5945@gmail.com>, viro@zeniv.linux.org.uk
Cc:     linux-fsdevel@vger.kernel.org, io-uring@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20200805110247.GA103385@ubuntu>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <b3cc7c68-a76d-8efd-4d2d-bd4c06efe177@kernel.dk>
Date:   Wed, 5 Aug 2020 06:50:31 -0600
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On 8/5/20 5:02 AM, Guoyu Huang wrote:
> loop_rw_iter() does not check whether the file has a read or
> write function. This can lead to NULL pointer dereference
> when the user passes in a file descriptor that does not have
> read or write function.
> 
> The crash log looks like this:
> 
> [   99.834071] BUG: kernel NULL pointer dereference, address: 0000000000000000
> [   99.835364] #PF: supervisor instruction fetch in kernel mode
> [   99.836522] #PF: error_code(0x0010) - not-present page
> [   99.837771] PGD 8000000079d62067 P4D 8000000079d62067 PUD 79d8c067 PMD 0
> [   99.839649] Oops: 0010 [#2] SMP PTI
> [   99.840591] CPU: 1 PID: 333 Comm: io_wqe_worker-0 Tainted: G      D           5.8.0 #2
> [   99.842622] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1 04/01/2014
> [   99.845140] RIP: 0010:0x0
> [   99.845840] Code: Bad RIP value.
> [   99.846672] RSP: 0018:ffffa1c7c01ebc08 EFLAGS: 00010202
> [   99.848018] RAX: 0000000000000000 RBX: ffff92363bd67300 RCX: ffff92363d461208
> [   99.849854] RDX: 0000000000000010 RSI: 00007ffdbf696bb0 RDI: ffff92363bd67300
> [   99.851743] RBP: ffffa1c7c01ebc40 R08: 0000000000000000 R09: 0000000000000000
> [   99.853394] R10: ffffffff9ec692a0 R11: 0000000000000000 R12: 0000000000000010
> [   99.855148] R13: 0000000000000000 R14: ffff92363d461208 R15: ffffa1c7c01ebc68
> [   99.856914] FS:  0000000000000000(0000) GS:ffff92363dd00000(0000) knlGS:0000000000000000
> [   99.858651] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   99.860032] CR2: ffffffffffffffd6 CR3: 000000007ac66000 CR4: 00000000000006e0
> [   99.861979] Call Trace:
> [   99.862617]  loop_rw_iter.part.0+0xad/0x110
> [   99.863838]  io_write+0x2ae/0x380
> [   99.864644]  ? kvm_sched_clock_read+0x11/0x20
> [   99.865595]  ? sched_clock+0x9/0x10
> [   99.866453]  ? sched_clock_cpu+0x11/0xb0
> [   99.867326]  ? newidle_balance+0x1d4/0x3c0
> [   99.868283]  io_issue_sqe+0xd8f/0x1340
> [   99.869216]  ? __switch_to+0x7f/0x450
> [   99.870280]  ? __switch_to_asm+0x42/0x70
> [   99.871254]  ? __switch_to_asm+0x36/0x70
> [   99.872133]  ? lock_timer_base+0x72/0xa0
> [   99.873155]  ? switch_mm_irqs_off+0x1bf/0x420
> [   99.874152]  io_wq_submit_work+0x64/0x180
> [   99.875192]  ? kthread_use_mm+0x71/0x100
> [   99.876132]  io_worker_handle_work+0x267/0x440
> [   99.877233]  io_wqe_worker+0x297/0x350
> [   99.878145]  kthread+0x112/0x150
> [   99.878849]  ? __io_worker_unuse+0x100/0x100
> [   99.879935]  ? kthread_park+0x90/0x90
> [   99.880874]  ret_from_fork+0x22/0x30
> [   99.881679] Modules linked in:
> [   99.882493] CR2: 0000000000000000
> [   99.883324] ---[ end trace 4453745f4673190b ]---
> [   99.884289] RIP: 0010:0x0
> [   99.884837] Code: Bad RIP value.
> [   99.885492] RSP: 0018:ffffa1c7c01ebc08 EFLAGS: 00010202
> [   99.886851] RAX: 0000000000000000 RBX: ffff92363acd7f00 RCX: ffff92363d461608
> [   99.888561] RDX: 0000000000000010 RSI: 00007ffe040d9e10 RDI: ffff92363acd7f00
> [   99.890203] RBP: ffffa1c7c01ebc40 R08: 0000000000000000 R09: 0000000000000000
> [   99.891907] R10: ffffffff9ec692a0 R11: 0000000000000000 R12: 0000000000000010
> [   99.894106] R13: 0000000000000000 R14: ffff92363d461608 R15: ffffa1c7c01ebc68
> [   99.896079] FS:  0000000000000000(0000) GS:ffff92363dd00000(0000) knlGS:0000000000000000
> [   99.898017] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   99.899197] CR2: ffffffffffffffd6 CR3: 000000007ac66000 CR4: 00000000000006e0

Thanks, applied (slightly modified for current -git), and marked with the right
fixes tag and stable CC'ed.

-- 
Jens Axboe