Re: [PATCH] binfmt_misc: fix shift-out-of-bounds in check_special_flags

[Al Viro]

On Wed, Nov 02, 2022 at 10:51:23AM +0800, Liu Shixin wrote:
> UBSAN reported a shift-out-of-bounds warning:
> 
>  left shift of 1 by 31 places cannot be represented in type 'int'
>  Call Trace:
>   <TASK>
>   __dump_stack lib/dump_stack.c:88 [inline]
>   dump_stack_lvl+0x8d/0xcf lib/dump_stack.c:106
>   ubsan_epilogue+0xa/0x44 lib/ubsan.c:151
>   __ubsan_handle_shift_out_of_bounds+0x1e7/0x208 lib/ubsan.c:322
>   check_special_flags fs/binfmt_misc.c:241 [inline]
>   create_entry fs/binfmt_misc.c:456 [inline]
>   bm_register_write+0x9d3/0xa20 fs/binfmt_misc.c:654
>   vfs_write+0x11e/0x580 fs/read_write.c:582
>   ksys_write+0xcf/0x120 fs/read_write.c:637
>   do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>   do_syscall_64+0x34/0x80 arch/x86/entry/common.c:80
>   entry_SYSCALL_64_after_hwframe+0x63/0xcd
>  RIP: 0033:0x4194e1
> 
> Since the type of Node's flags is unsigned long, we should define these
> macros with same type too.

We are limited to 32 bits anyway.  More interesting question here is what's
the point of having those bits that high anyway?