On Thu, Aug 01, 2024 at 01:28:37PM +0800, Lizhi Xu wrote: > > > syzbot report KMSAN: uninit-value in pick_link, this is because the > > > corresponding folio was not found from the mapping, and the memory was > > > not initialized when allocating a new folio for the filemap. > > > > > > To avoid the occurrence of kmsan report uninit-value, initialize the > > > newly allocated folio memory to 0. > > > > NAK. > > > > You are papering over the real bug here. > Did you see the splat? I think you didn't see that. Sigh... It is stepping into uninitialized data in pick_link(), and by the look of traces it's been created by page_get_link(). What page_get_link() does is reading from page cache of symlink; the contents should have come from ->read_folio() (if it's really a symlink on squashfs, that would be squashfs_symlink_read_folio()). Uninit might have happened if * ->read_folio() hadn't been called at all (which is an obvios bug - that's what should've read the symlink contents) or * ->read_folio() had been called, it failed and yet we are still trying to use the resulting page. Again, an obvious bug - if trying to read fails, we should _not_ use the results or leave it in page cache for subsequent callers. * ->read_folio() had been called, claimed to have succeeded and yet it had left something in range 0..inode->i_size-1 uninitialized. Again, a bug, this time in ->read_folio() instance. Your patch is basically "fill the page with zeroes before reading anything into it". It makes KMSAM warning STFU, but it does not fix anything in any of those cases.
