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Subject: Re: [PATCH] serial: 8250: fix null-ptr-deref in serial8250_start_tx()
To:     Greg KH <gregkh@linuxfoundation.org>
CC:     <linux-serial@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <jslaby@suse.com>, Hanjun Guo <guohanjun@huawei.com>,
        "Libin (Huawei)" <huawei.libin@huawei.com>
References: <20200721143852.4058352-1-yangyingliang@huawei.com>
 <20200721104819.GA1678476@kroah.com>
From:   Yang Yingliang <yangyingliang@huawei.com>
Message-ID: <b0cbee3f-05cd-b15c-06db-68c223c9944c@huawei.com>
Date:   Tue, 21 Jul 2020 19:54:51 +0800
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On 2020/7/21 18:48, Greg KH wrote:
> On Tue, Jul 21, 2020 at 02:38:52PM +0000, Yang Yingliang wrote:
>> I got null-ptr-deref in serial8250_start_tx():
>>
>> [   78.114630] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
>> [   78.123778] Mem abort info:
>> [   78.126560]   ESR = 0x86000007
>> [   78.129603]   EC = 0x21: IABT (current EL), IL = 32 bits
>> [   78.134891]   SET = 0, FnV = 0
>> [   78.137933]   EA = 0, S1PTW = 0
>> [   78.141064] user pgtable: 64k pages, 48-bit VAs, pgdp=00000027d41a8600
>> [   78.147562] [0000000000000000] pgd=00000027893f0003, p4d=00000027893f0003, pud=00000027893f0003, pmd=00000027c9a20003, pte=0000000000000000
>> [   78.160029] Internal error: Oops: 86000007 [#1] SMP
>> [   78.164886] Modules linked in: sunrpc vfat fat aes_ce_blk crypto_simd cryptd aes_ce_cipher crct10dif_ce ghash_ce sha2_ce sha256_arm64 sha1_ce ses enclosure sg sbsa_gwdt ipmi_ssif spi_dw_mmio sch_fq_codel vhost_net tun vhost vhost_iotlb tap ip_tables ext4 mbcache jbd2 ahci hisi_sas_v3_hw libahci hisi_sas_main libsas hns3 scsi_transport_sas hclge libata megaraid_sas ipmi_si hnae3 ipmi_devintf ipmi_msghandler br_netfilter bridge stp llc nvme nvme_core xt_sctp sctp libcrc32c dm_mod nbd
>> [   78.207383] CPU: 11 PID: 23258 Comm: null-ptr Not tainted 5.8.0-rc6+ #48
>> [   78.214056] Hardware name: Huawei TaiShan 2280 V2/BC82AMDC, BIOS 2280-V2 CS V3.B210.01 03/12/2020
>> [   78.222888] pstate: 80400089 (Nzcv daIf +PAN -UAO BTYPE=--)
>> [   78.228435] pc : 0x0
>> [   78.230618] lr : serial8250_start_tx+0x160/0x260
>> [   78.235215] sp : ffff800062eefb80
>> [   78.238517] x29: ffff800062eefb80 x28: 0000000000000fff
>> [   78.243807] x27: ffff800062eefd80 x26: ffff202fd83b3000
>> [   78.249098] x25: ffff800062eefd80 x24: ffff202fd83b3000
>> [   78.254388] x23: ffff002fc5e50be8 x22: 0000000000000002
>> [   78.259679] x21: 0000000000000001 x20: 0000000000000000
>> [   78.264969] x19: ffffa688827eecc8 x18: 0000000000000000
>> [   78.270259] x17: 0000000000000000 x16: 0000000000000000
>> [   78.275550] x15: ffffa68881bc67a8 x14: 00000000000002e6
>> [   78.280841] x13: ffffa68881bc67a8 x12: 000000000000c539
>> [   78.286131] x11: d37a6f4de9bd37a7 x10: ffffa68881cccff0
>> [   78.291421] x9 : ffffa68881bc6000 x8 : ffffa688819daa88
>> [   78.296711] x7 : ffffa688822a0f20 x6 : ffffa688819e0000
>> [   78.302002] x5 : ffff800062eef9d0 x4 : ffffa68881e707a8
>> [   78.307292] x3 : 0000000000000000 x2 : 0000000000000002
>> [   78.312582] x1 : 0000000000000001 x0 : ffffa688827eecc8
>> [   78.317873] Call trace:
>> [   78.320312]  0x0
>> [   78.322147]  __uart_start.isra.9+0x64/0x78
>> [   78.326229]  uart_start+0xb8/0x1c8
>> [   78.329620]  uart_flush_chars+0x24/0x30
>> [   78.333442]  n_tty_receive_buf_common+0x7b0/0xc30
>> [   78.338128]  n_tty_receive_buf+0x44/0x2c8
>> [   78.342122]  tty_ioctl+0x348/0x11f8
>> [   78.345599]  ksys_ioctl+0xd8/0xf8
>> [   78.348903]  __arm64_sys_ioctl+0x2c/0xc8
>> [   78.352812]  el0_svc_common.constprop.2+0x88/0x1b0
>> [   78.357583]  do_el0_svc+0x44/0xd0
>> [   78.360887]  el0_sync_handler+0x14c/0x1d0
>> [   78.364880]  el0_sync+0x140/0x180
>> [   78.368185] Code: bad PC value
>>
>> SERIAL_PORT_DFNS is not defined on each arch, if it's not defined,
>> serial8250_set_defaults() won't be called in serial8250_isa_init_ports(),
>> so the p->serial_in pointer won't be initialized, and it leads a null-ptr-deref.
>> Fix this problem by calling serial8250_set_defaults() after init uart port.
>>
>> Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
>> ---
>>   drivers/tty/serial/8250/8250_core.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
> Does this fix a specific commit, or has this issue always been present?
> What has caused it to happen now that no one else has seen this?

I think it's always been present on the arch that not defined 
SERIAL_PORT_DFNS.

I got this on arm64 and here is the C reproducer:

// autogenerated by syzkaller (https://github.com/google/syzkaller)

#define _GNU_SOURCE

#include <endian.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>

#ifndef __NR_ioctl
#define __NR_ioctl 29
#endif
#ifndef __NR_mmap
#define __NR_mmap 222
#endif
#ifndef __NR_openat
#define __NR_openat 56
#endif

uint64_t r[1] = {0xffffffffffffffff};

int main(void)
{
     syscall(__NR_mmap, 0x20000000ul, 0x1000000ul, 3ul, 0x32ul, -1, 0);
     intptr_t res = 0;
     memcpy((void*)0x20000040, "/dev/ttyS3\000", 11);
     res = syscall(__NR_openat, 0xffffffffffffff9cul, 0x20000040ul, 
0x401ul, 0ul);
     if (res != -1)
         r[0] = res;
     syscall(__NR_ioctl, r[0], 0x5412ul, 0x20000080ul);
     return 0;
}


Thanks,

Yang

>
> thanks,
>
> greg k-h
> .