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loop, zloop: fix dma_alignment for large or unreported limits

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A file system sets STATX_DIOALIGN with zeroed alignments when the file
can't be used for direct I/O. The zero underflowed to UINT_MAX and
triggered a queue limits validation warning. Fall back to the block
device's limits when dio_mem_align isn't reported.

A file system with a block size larger than PAGE_SIZE may also report a
memory alignment that can't be expressed as a queue limit. File systems
fall back to buffered I/O for requests that don't meet their alignment,
so cap the reported limit to the largest possible value.

Fixes: 6c8dec275c ("loop: set dma_alignment from the backing file for direct I/O")
Fixes: c5059c1af2 ("zloop: set dma_alignment from the backing files for direct I/O")
Reported-by: syzbot+ac00e7bf7ac8c91af921@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=ac00e7bf7ac8c91af921
Signed-off-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://patch.msgid.link/20260810164218.3721636-1-kbusch@meta.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Keith Busch 2026-08-10 09:42:17 -07:00 committed by Jens Axboe
parent 96c8ea3c5a
commit e52349a5ea
2 changed files with 10 additions and 6 deletions
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8
drivers/block/loop.c
View File

@ -458,12 +458,14 @@ static void loop_update_dio_alignment(struct loop_device *lo)
* Use the dio alignment of the file system if provided. The incomoing
* request's bio_vec is forwarded to the backing file unchanged, so its
* required memory alignment becomes the device's dma_alignment when
* used for direct-io.
* used for direct-io. The file system reports zeroed alignments if the
* file can't be used for direct-io at all, so fall back to the block
* device limits in that case.
*/
if (!vfs_getattr(&file->f_path, &st, STATX_DIOALIGN, 0) &&
(st.result_mask & STATX_DIOALIGN)) {
(st.result_mask & STATX_DIOALIGN) && st.dio_mem_align) {
lo->lo_min_dio_size = st.dio_offset_align;
lo->lo_dio_mem_align = st.dio_mem_align - 1;
lo->lo_dio_mem_align = min(st.dio_mem_align - 1, PAGE_SIZE - 1);
return;
}

8
drivers/block/zloop.c
View File

@ -1042,12 +1042,14 @@ static int zloop_get_block_size(struct zloop_device *zlo,
* Use the dio alignment of the file system if provided. The incoming
* request's bio_vec is forwarded to the backing file unchanged, so its
* required memory alignment becomes the device's dma_alignment when
* used for direct-io.
* used for direct-io. The file system reports zeroed alignments if the
* file can't be used for direct-io at all, so fall back to the block
* device limits in that case.
*/
if (!vfs_getattr(&zone->file->f_path, &st, STATX_DIOALIGN, 0) &&
(st.result_mask & STATX_DIOALIGN)) {
(st.result_mask & STATX_DIOALIGN) && st.dio_mem_align) {
zlo->block_size = st.dio_offset_align;
zlo->dio_mem_align = st.dio_mem_align - 1;
zlo->dio_mem_align = min(st.dio_mem_align - 1, PAGE_SIZE - 1);
} else if (sb_bdev) {
zlo->block_size = bdev_physical_block_size(sb_bdev);
zlo->dio_mem_align = bdev_dma_alignment(sb_bdev);