Re: [PATCH] do_sys_name_to_handle(): use kzalloc() to fix kernel-infoleak

[Jan Kara]

On Fri 19-01-24 07:39:06, Nikita Zhandarovich wrote:
> syzbot identified a kernel information leak vulnerability in
> do_sys_name_to_handle() and issued the following report [1].
> 
> [1]
> "BUG: KMSAN: kernel-infoleak in instrument_copy_to_user include/linux/instrumented.h:114 [inline]
> BUG: KMSAN: kernel-infoleak in _copy_to_user+0xbc/0x100 lib/usercopy.c:40
>  instrument_copy_to_user include/linux/instrumented.h:114 [inline]
>  _copy_to_user+0xbc/0x100 lib/usercopy.c:40
>  copy_to_user include/linux/uaccess.h:191 [inline]
>  do_sys_name_to_handle fs/fhandle.c:73 [inline]
>  __do_sys_name_to_handle_at fs/fhandle.c:112 [inline]
>  __se_sys_name_to_handle_at+0x949/0xb10 fs/fhandle.c:94
>  __x64_sys_name_to_handle_at+0xe4/0x140 fs/fhandle.c:94
>  ...
> 
> Uninit was created at:
>  slab_post_alloc_hook+0x129/0xa70 mm/slab.h:768
>  slab_alloc_node mm/slub.c:3478 [inline]
>  __kmem_cache_alloc_node+0x5c9/0x970 mm/slub.c:3517
>  __do_kmalloc_node mm/slab_common.c:1006 [inline]
>  __kmalloc+0x121/0x3c0 mm/slab_common.c:1020
>  kmalloc include/linux/slab.h:604 [inline]
>  do_sys_name_to_handle fs/fhandle.c:39 [inline]
>  __do_sys_name_to_handle_at fs/fhandle.c:112 [inline]
>  __se_sys_name_to_handle_at+0x441/0xb10 fs/fhandle.c:94
>  __x64_sys_name_to_handle_at+0xe4/0x140 fs/fhandle.c:94
>  ...
> 
> Bytes 18-19 of 20 are uninitialized
> Memory access of size 20 starts at ffff888128a46380
> Data copied to user address 0000000020000240"
> 
> Per Chuck Lever's suggestion, use kzalloc() instead of kmalloc() to
> solve the problem.
> 
> Fixes: 990d6c2d7aee ("vfs: Add name to file handle conversion support")
> Suggested-by: Chuck Lever III <chuck.lever@xxxxxxxxxx>
> Reported-and-tested-by: syzbot+09b349b3066c2e0b1e96@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Nikita Zhandarovich <n.zhandarovich@xxxxxxxxxx>

Makes sense. Feel free to add:

Reviewed-by: Jan Kara <jack@xxxxxxx>

								Honza

> ---
> Link to Chuck's suggestion: 
> https://lore.kernel.org/all/B4A8D625-6997-49C8-B105-B2DCFE8C6DDA@xxxxxxxxxx/
> 
>  fs/fhandle.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/fhandle.c b/fs/fhandle.c
> index 18b3ba8dc8ea..57a12614addf 100644
> --- a/fs/fhandle.c
> +++ b/fs/fhandle.c
> @@ -36,7 +36,7 @@ static long do_sys_name_to_handle(const struct path *path,
>  	if (f_handle.handle_bytes > MAX_HANDLE_SZ)
>  		return -EINVAL;
>  
> -	handle = kmalloc(sizeof(struct file_handle) + f_handle.handle_bytes,
> +	handle = kzalloc(sizeof(struct file_handle) + f_handle.handle_bytes,
>  			 GFP_KERNEL);
>  	if (!handle)
>  		return -ENOMEM;
> -- 
> 2.25.1
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR