On Mon 06-08-18 15:59:27, Andrew Morton wrote: > On Mon, 6 Aug 2018 12:22:03 +0200 Jan Kara <jack@xxxxxxx> wrote: > > > On Fri 20-07-18 16:14:29, Andrew Morton wrote: > > > On Thu, 19 Jul 2018 10:58:12 +0200 Jan Kara <jack@xxxxxxx> wrote: > > > > > > > On Thu 19-07-18 16:17:26, Chengguang Xu wrote: > > > > > When we try to truncate read count in generic_file_buffered_read(), > > > > > should deliver (sb->s_maxbytes - offset) as maximum count not > > > > > sb->s_maxbytes itself. > > > > > > > > > > Signed-off-by: Chengguang Xu <cgxu519@xxxxxxx> > > > > > > > > Looks good to me. You can add: > > > > > > > > Reviewed-by: Jan Kara <jack@xxxxxxx> > > > > > > Yup. > > > > > > What are the runtime effects of this bug? > > > > Good question. I think ->readpage() could be called for index beyond > > maximum file size supported by the filesystem leading to weird filesystem > > behavior due to overflows in internal calculations. > > > > Sure. But is it possible for userspace to trigger this behaviour? > Possibly all callers have already sanitized the arguments by this stage > in which case the statement is arguably redundant. So I don't think there's any sanitization going on before generic_file_buffered_read(). E.g. I don't see any s_maxbytes check on ksys_read() -> vfs_read() -> __vfs_read() -> new_sync_read() -> call_read_iter() -> generic_file_read_iter() -> generic_file_buffered_read() path... However now thinking about this again: We are guaranteed i_size is within s_maxbytes (places modifying i_size are checking for this) and generic_file_buffered_read() stops when it should read beyond i_size. So in the end I don't think there's any breakage possible and the patch is not necessary? Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
