From: "Darrick J. Wong" djwong@kernel.org
mainline inclusion from mainline-v5.19-rc1 commit e9c3a8e820ed0eeb2be05072f29f80d1b79f053b category: bugfix bugzilla: 188775, https://gitee.com/openeuler/kernel/issues/I73IFH
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
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XFS has the unique behavior (as compared to the other Linux filesystems) that on writeback errors it will completely invalidate the affected folio and force the page cache to reread the contents from disk. All other filesystems leave the page mapped and up to date.
This is a rude awakening for user programs, since (in the case where write fails but reread doesn't) file contents will appear to revert to old disk contents with no notification other than an EIO on fsync. This might have been annoying back in the days when iomap dealt with one page at a time, but with multipage folios, we can now throw away *megabytes* worth of data for a single write error.
On *most* Linux filesystems, a program can respond to an EIO on write by redirtying the entire file and scheduling it for writeback. This isn't foolproof, since the page that failed writeback is no longer dirty and could be evicted, but programs that want to recover properly *also* have to detect XFS and regenerate every write they've made to the file.
When running xfs/314 on arm64, I noticed a UAF when xfs_discard_folio invalidates multipage folios that could be undergoing writeback. If, say, we have a 256K folio caching a mix of written and unwritten extents, it's possible that we could start writeback of the first (say) 64K of the folio and then hit a writeback error on the next 64K. We then free the iop attached to the folio, which is really bad because writeback completion on the first 64k will trip over the "blocks per folio > 1 && !iop" assertion.
This can't be fixed by only invalidating the folio if writeback fails at the start of the folio, since the folio is marked !uptodate, which trips other assertions elsewhere. Get rid of the whole behavior entirely.
Signed-off-by: Darrick J. Wong djwong@kernel.org Reviewed-by: Matthew Wilcox (Oracle) willy@infradead.org Reviewed-by: Jeff Layton jlayton@kernel.org Reviewed-by: Christoph Hellwig hch@lst.de
Conflicts: fs/xfs/xfs_aops.c fs/iomap/buffered-io.c
Signed-off-by: Baokun Li libaokun1@huawei.com Reviewed-by: Yang Erkun yangerkun@huawei.com Reviewed-by: Zhang Yi yi.zhang@huawei.com Signed-off-by: Jialin Zhang zhangjialin11@huawei.com --- fs/iomap/buffered-io.c | 1 - fs/xfs/xfs_aops.c | 4 +--- 2 files changed, 1 insertion(+), 4 deletions(-)
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c index 0b110f3aa703..2209ce39511f 100644 --- a/fs/iomap/buffered-io.c +++ b/fs/iomap/buffered-io.c @@ -1433,7 +1433,6 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc, if (wpc->ops->discard_page) wpc->ops->discard_page(page, file_offset); if (!count) { - ClearPageUptodate(page); unlock_page(page); goto done; } diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c index d4d531c78ae4..fecb1fddcc79 100644 --- a/fs/xfs/xfs_aops.c +++ b/fs/xfs/xfs_aops.c @@ -525,7 +525,7 @@ xfs_discard_page( int error;
if (XFS_FORCED_SHUTDOWN(mp)) - goto out_invalidate; + return;
xfs_alert_ratelimited(mp, "page discard on page "PTR_FMT", inode 0x%llx, offset %llu.", @@ -535,8 +535,6 @@ xfs_discard_page( i_blocks_per_page(inode, page) - pageoff_fsb); if (error && !XFS_FORCED_SHUTDOWN(mp)) xfs_alert(mp, "page discard unable to remove delalloc mapping."); -out_invalidate: - iomap_invalidatepage(page, pageoff, PAGE_SIZE - pageoff); }
static const struct iomap_writeback_ops xfs_writeback_ops = {