From: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx> commit fee5eaecca86afa544355569b831c1f90f334b85 upstream. Syzbot reports that in its stress test for resize ioctl, the log writing function nilfs_segctor_do_construct hits a WARN_ON in nilfs_segctor_truncate_segments(). It turned out that there is a problem with the current implementation of the resize ioctl, which changes the writable range on the device (the range of allocatable segments) at the end of the resize process. This order is necessary for file system expansion to avoid corrupting the superblock at trailing edge. However, in the case of a file system shrink, if log writes occur after truncating out-of-bounds trailing segments and before the resize is complete, segments may be allocated from the truncated space. The userspace resize tool was fine as it limits the range of allocatable segments before performing the resize, but it can run into this issue if the resize ioctl is called alone. Fix this issue by changing nilfs_sufile_resize() to update the range of allocatable segments immediately after successful truncation of segment space in case of file system shrink. Link: https://lkml.kernel.org/r/20230524094348.3784-1-konishi.ryusuke@xxxxxxxxx Fixes: 4e33f9eab07e ("nilfs2: implement resize ioctl") Signed-off-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx> Reported-by: syzbot+33494cd0df2ec2931851@xxxxxxxxxxxxxxxxxxxxxxxxx Closes: https://lkml.kernel.org/r/0000000000005434c405fbbafdc5@xxxxxxxxxx Tested-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- fs/nilfs2/sufile.c | 9 +++++++++ 1 file changed, 9 insertions(+) --- a/fs/nilfs2/sufile.c +++ b/fs/nilfs2/sufile.c @@ -782,6 +782,15 @@ int nilfs_sufile_resize(struct inode *su goto out_header; sui->ncleansegs -= nsegs - newnsegs; + + /* + * If the sufile is successfully truncated, immediately adjust + * the segment allocation space while locking the semaphore + * "mi_sem" so that nilfs_sufile_alloc() never allocates + * segments in the truncated space. + */ + sui->allocmax = newnsegs - 1; + sui->allocmin = 0; } kaddr = kmap_atomic(header_bh->b_page);
