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Patch series "Fixes and cleanups to xarray", v3.
This series contains some random fixes and cleanups to xarray. Patch 1-2
are fixes and patch 3-6 are cleanups. More details can be found in
respective patches.
This patch (of 5):
Similar to issue fixed in commit cbc02854331ed ("XArray: Do not return
sibling entries from xa_load()"), we may return sibling entries from
xas_find_marked as following:
Thread A: Thread B:
xa_store_range(xa, entry, 6, 7, gfp);
xa_set_mark(xa, 6, mark)
XA_STATE(xas, xa, 6);
xas_find_marked(&xas, 7, mark);
offset = xas_find_chunk(xas, advance, mark);
[offset is 6 which points to a valid entry]
xa_store_range(xa, entry, 4, 7, gfp);
entry = xa_entry(xa, node, 6);
[entry is a sibling of 4]
if (!xa_is_node(entry))
return entry;
Skip sibling entry like xas_find() does to protect caller from seeing
sibling entry from xas_find_marked() or caller may use sibling entry as a
valid entry and crash the kernel.
Besides, load_race() test is modified to catch mentioned issue and
modified load_race() only passes after this fix is merged.
Here is an example how this bug could be triggerred in theory in nfs which
enables large folio in mapping:
Let's take a look at involved racer:
1. How pages could be created and dirtied in nfs.
write
ksys_write
vfs_write
new_sync_write
nfs_file_write
generic_perform_write
nfs_write_begin
fgf_set_order
__filemap_get_folio
nfs_write_end
nfs_update_folio
nfs_writepage_setup
nfs_mark_request_dirty
filemap_dirty_folio
__folio_mark_dirty
__xa_set_mark
2. How dirty pages could be deleted in nfs.
ioctl
do_vfs_ioctl
file_ioctl
ioctl_preallocate
vfs_fallocate
nfs42_fallocate
nfs42_proc_deallocate
truncate_pagecache_range
truncate_inode_pages_range
truncate_inode_folio
filemap_remove_folio
page_cache_delete
xas_store(&xas, NULL);
3. How dirty pages could be lockless searched
sync_file_range
ksys_sync_file_range
__filemap_fdatawrite_range
filemap_fdatawrite_wbc
do_writepages
writeback_use_writepage
writeback_iter
writeback_get_folio
filemap_get_folios_tag
find_get_entry
folio = xas_find_marked()
folio_try_get(folio)
In theory, kernel will crash as following:
1.Create 2.Search 3.Delete
/* write page 2,3 */
write
...
nfs_write_begin
fgf_set_order
__filemap_get_folio
...
/* index = 2, order = 1 */
xa_store(&xas, folio)
nfs_write_end
...
__folio_mark_dirty
/* sync page 2 and page 3 */
sync_file_range
...
find_get_entry
folio = xas_find_marked()
/* offset will be 2 */
offset = xas_find_chunk()
/* delete page 2 and page 3 */
ioctl
...
xas_store(&xas, NULL);
/* write page 0-3 */
write
...
nfs_write_begin
fgf_set_order
__filemap_get_folio
...
/* index = 0, order = 2 */
xa_store(&xas, folio)
nfs_write_end
...
__folio_mark_dirty
/* get sibling entry from offset 2 */
entry = xa_entry(.., 2)
/* use sibling entry as folio and crash kernel */
folio_try_get(folio)
Link: https://lkml.kernel.org/r/20241218154613.58754-2-shikemeng@huaweicloud.com
Link: https://lkml.kernel.org/r/20241213122523.12764-1-shikemeng@huaweicloud.com
Link: https://lkml.kernel.org/r/20241213122523.12764-2-shikemeng@huaweicloud.com
Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>