Re: CVE-2024-41001: io_uring/sqpoll: work around a potential audit memory leak

[Wang Zhaolong <wangzhaolong1@huawei.com>]

Hello,

I was confused when reviewing the fix for CVE-2024-41001.
To better understand the issue and the proposed solution, I would
greatly appreciate your help in clarifying the following points:

1. What was the original patch that introduced this issue (any Fixes tag)?
2. Is the leaking variable member the "context->sockaddr"?
3. Could you shed some light on how the reference to the leaked memory is
    lost during the transition from the prep phase to the issue phase?
4. The fix introduces a NOP operation "before the SQPOLL does anything."
    How does this addition of a NOP operation prevent the memory leak from
    occurring?

Thank you in advance for taking the time to address my questions. Your
insights will help me better understand this fix.

Best regards,
Wang Zhaolong

> Description
> ===========
> 
> In the Linux kernel, the following vulnerability has been resolved:
> 
> io_uring/sqpoll: work around a potential audit memory leak
> 
> kmemleak complains that there's a memory leak related to connect
> handling:
> 
> unreferenced object 0xffff0001093bdf00 (size 128):
> comm "iou-sqp-455", pid 457, jiffies 4294894164
> hex dump (first 32 bytes):
> 02 00 fa ea 7f 00 00 01 00 00 00 00 00 00 00 00  ................
> 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> backtrace (crc 2e481b1a):
> [<00000000c0a26af4>] kmemleak_alloc+0x30/0x38
> [<000000009c30bb45>] kmalloc_trace+0x228/0x358
> [<000000009da9d39f>] __audit_sockaddr+0xd0/0x138
> [<0000000089a93e34>] move_addr_to_kernel+0x1a0/0x1f8
> [<000000000b4e80e6>] io_connect_prep+0x1ec/0x2d4
> [<00000000abfbcd99>] io_submit_sqes+0x588/0x1e48
> [<00000000e7c25e07>] io_sq_thread+0x8a4/0x10e4
> [<00000000d999b491>] ret_from_fork+0x10/0x20
> 
> which can can happen if:
> 
> 1) The command type does something on the prep side that triggers an
>     audit call.
> 2) The thread hasn't done any operations before this that triggered
>     an audit call inside ->issue(), where we have audit_uring_entry()
>     and audit_uring_exit().
> 
> Work around this by issuing a blanket NOP operation before the SQPOLL
> does anything.
> 
> The Linux kernel CVE team has assigned CVE-2024-41001 to this issue.