Re: [PATCH next] fs: fix oob in do_handle_open

["Gustavo A. R. Silva" <gustavo@embeddedor.com>]

On 03/04/24 02:48, Jeff Layton wrote:
> On Wed, 2024-04-03 at 14:54 +0800, Edward Adam Davis wrote:
>> [Syzbot reported]
>> BUG: KASAN: slab-out-of-bounds in instrument_copy_from_user_before include/linux/instrumented.h:129 [inline]
>> BUG: KASAN: slab-out-of-bounds in _copy_from_user+0x7b/0xe0 lib/usercopy.c:22
>> Write of size 48 at addr ffff88802b8cbc88 by task syz-executor333/5090
>>
>> CPU: 0 PID: 5090 Comm: syz-executor333 Not tainted 6.9.0-rc2-next-20240402-syzkaller #0
>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
>> Call Trace:
>>   <TASK>
>>   __dump_stack lib/dump_stack.c:88 [inline]
>>   dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
>>   print_address_description mm/kasan/report.c:377 [inline]
>>   print_report+0x169/0x550 mm/kasan/report.c:488
>>   kasan_report+0x143/0x180 mm/kasan/report.c:601
>>   kasan_check_range+0x282/0x290 mm/kasan/generic.c:189
>>   instrument_copy_from_user_before include/linux/instrumented.h:129 [inline]
>>   _copy_from_user+0x7b/0xe0 lib/usercopy.c:22
>>   copy_from_user include/linux/uaccess.h:183 [inline]
>>   handle_to_path fs/fhandle.c:203 [inline]
>>   do_handle_open+0x204/0x660 fs/fhandle.c:226
>>   do_syscall_64+0xfb/0x240
>>   entry_SYSCALL_64_after_hwframe+0x72/0x7a
>> [Fix]
>> When copying data to f_handle, the length of the copied data should not include
>> the length of "struct file_handle".
>>
>> Reported-by: syzbot+4139435cb1b34cf759c2@syzkaller.appspotmail.com
>> Signed-off-by: Edward Adam Davis <eadavis@qq.com>
>> ---
>>   fs/fhandle.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/fhandle.c b/fs/fhandle.c
>> index 53ed54711cd2..8a7f86c2139a 100644
>> --- a/fs/fhandle.c
>> +++ b/fs/fhandle.c
>> @@ -202,7 +202,7 @@ static int handle_to_path(int mountdirfd, struct file_handle __user *ufh,
>>   	*handle = f_handle;
>>   	if (copy_from_user(&handle->f_handle,
>>   			   &ufh->f_handle,
>> -			   struct_size(ufh, f_handle, f_handle.handle_bytes))) {
>> +			   f_handle.handle_bytes)) {
>>   		retval = -EFAULT;
>>   		goto out_handle;
>>   	}
> 
> cc'ing Gustavo, since it looks like his patch in -next is what broke
> this.
> 

Oh, sorry about that folks. That looks pretty much like a copy/paste error.

The fix is correct.

Thanks, Edward!
--
Gustavo