Re: Fwd: [EXTERNAL] Re: ioctl.c:undefined reference to `__get_user_bad'

[Randy Dunlap <rdunlap@infradead.org>]

[adding back linux-arm-kernel; what happened to it? ]


On 5/17/21 2:04 PM, Randy Dunlap wrote:
> On 5/17/21 10:13 AM, Steve French wrote:
>>> If you fix the issue, kindly add following tag as appropriate
>>> Reported-by: kernel test robot <lkp@intel.com>
>>>
>>> All errors (new ones prefixed by >>):
>>>
>>>    arm-linux-gnueabi-ld: fs/cifs/ioctl.o: in function `cifs_dump_full_key':
>>>>> ioctl.c:(.text+0x44): undefined reference to `__get_user_bad'
>>>
>>
>> <snip>
>>
>>> # CONFIG_MMU is not set
>>>
>>> and arch/arm/include/asm/uaccess.h does not implement get_user(size 8 bytes)
>>> for the non-MMU case:
>>
>> I see another place in fs/cifs/ioctl.c where we already had been doing
>> a get_user() into a u64 - any idea what you are supposed to do
>> instead?  Any example code where people have worked around this.
> 
> Hi Steve,
> 
> This change in cifs_dump_full_key() makes it build OK:
> 
> -       if (get_user(suid, (__u64 __user *)arg))
> +       if (get_user(suid, (unsigned int __user *)arg))
> 
> 
> That is what the other call uses:
> 
> 		case FS_IOC_SETFLAGS:
> 			cifs_dbg(VFS, "cifs ioctl FS_IOC_SETFLAGS:\n");
> 			if (pSMBFile == NULL)
> 				break;
> 			tcon = tlink_tcon(pSMBFile->tlink);
> 			caps = le64_to_cpu(tcon->fsUnixInfo.Capability);
> 
> 			if (get_user(ExtAttrBits, (int __user *)arg)) {
> 				rc = -EFAULT;
> 				break;
> 			}
> 
> However, my reading/understanding is that the one immediately above
> is incorrect, as is the -/+ patch above it, since get_user() gets its
> data size (1, 2, 4, 8) from the type of the pointer that is passed to it.
> For 8 bytes (64 bits), 'int' is not sufficient, so IMO the get_user()
> call that builds:
> 			if (get_user(ExtAttrBits, (int __user *)arg)) {
> is a bug. It should be:
> 			if (get_user(ExtAttrBits, (__u64 __user *)arg)) {
> and if I make that latter change in the source file, the build says:
> 
> arm-linux-gnueabi-ld: fs/cifs/ioctl.o: in function `cifs_dump_full_key':
> ioctl.c:(.text+0x14): undefined reference to `__get_user_bad'
> arm-linux-gnueabi-ld: fs/cifs/ioctl.o: in function `cifs_ioctl':
> ioctl.c:(.text+0x1f2): undefined reference to `__get_user_bad'
> 
> so now both of them fail on the get_user() of 8 bytes.
> 
> Hope that clarifies things.  It tells me that arm no-MMU still
> needs support for get_user() of size 8 bytes.
> 

-- 
~Randy


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