On 2025/5/1 19:19, Jan Kara wrote: > On Wed 30-04-25 04:14:32, Matthew Wilcox wrote: >> On Tue, Apr 29, 2025 at 03:55:18PM +0800, Zhang Yi wrote: >>> After debugging, I found that this problem is caused by punching a hole >>> with an offset variable larger than max_end on a corrupted ext4 inode, >>> whose i_size is larger than maxbyte. It will result in a negative length >>> in the truncate_inode_partial_folio(), which will trigger this problem. >> >> It seems to me like we're asking for trouble when we allow an inode with >> an i_size larger than max_end to be instantiated. There are probably >> other places which assume it is smaller than max_end. We should probably >> decline to create the bad inode in the first place? > > Indeed somewhat less quirky fix could be to make ext4_max_bitmap_size() > return one block smaller limit. Something like: > > /* Compute how many blocks we can address by block tree */ > res += ppb; > res += ppb * ppb; > res += ((loff_t)ppb) * ppb * ppb; > + /* > + * Hole punching assumes it can map the block past end of hole to > + * tree offsets > + */ > + res -= 1; > /* Compute how many metadata blocks are needed */ > meta_blocks = 1; > meta_blocks += 1 + ppb; > > The slight caveat is that in theory there could be filesystems out there > with so large files and then we'd stop allowing access to such files. But I > guess the chances are so low that it's probably worth trying. > Hmm, I suppose this approach could pose some risks to our legacy products, and it makes me feel uneasy. Personally, I am more inclined toward the current solution, unless we decide to fix the ext4_ind_remove_space() directly. :) Thanks, Yi.
