CVE-2025-21631: In the Linux kernel, the following vulnerability has been resolved:  block, bfq: fix waker_bfqq UAF after bfq_split_bfqq()  Our syzkaller report a following UAF for v6.6:  BUG: KASAN: slab-use-after-free in bfq_init_rq+0x175d/0x17a0 block/bfq-iosched.c:6958 Read of size 8 at addr ffff8881b57147d8 by task fsstress/232726  CPU: 2 PID: 232726 Comm: fsstress Not tainted 6.6.0-g3629d1885222 #39 Call Trace:  <TASK>  __dump_stack lib/dump_stack.c:88 [inline]  dump_stack_lvl+0x91/0xf0 lib/dump_stack.c:106  print_address_description.constprop.0+0x66/0x300 mm/kasan/report.c:364  print_report+0x3e/0x70 mm/kasan/report.c:475  kasan_report+0xb8/0xf0 mm/kasan/report.c:588  hlist_add_head include/linux/list.h:1023 [inline]  bfq_init_rq+0x175d/0x17a0 block/bfq-iosched.c:6958  bfq_insert_request.isra.0+0xe8/0xa20 block/bfq-iosched.c:6271  bfq_insert_requests+0x27f/0x390 block/bfq-iosched.c:6323  blk_mq_insert_request+0x290/0x8f0 block/blk-mq.c:2660  blk_mq_submit_bio+0x1021/0x15e0 block/blk-mq.c:3143  __submit_bio+0xa0/0x6b0 block/blk-core.c:639  __submit_bio_noacct_mq block/blk-core.c:718 [inline]  submit_bio_noacct_nocheck+0x5b7/0x810 block/blk-core.c:747  submit_bio_noacct+0xca0/0x1990 block/blk-core.c:847  __ext4_read_bh fs/ext4/super.c:205 [inline]  ext4_read_bh+0x15e/0x2e0 fs/ext4/super.c:230  __read_extent_tree_block+0x304/0x6f0 fs/ext4/extents.c:567  ext4_find_extent+0x479/0xd20 fs/ext4/extents.c:947  ext4_ext_map_blocks+0x1a3/0x2680 fs/ext4/extents.c:4182  ext4_map_blocks+0x929/0x15a0 fs/ext4/inode.c:660  ext4_iomap_begin_report+0x298/0x480 fs/ext4/inode.c:3569  iomap_iter+0x3dd/0x1010 fs/iomap/iter.c:91  iomap_fiemap+0x1f4/0x360 fs/iomap/fiemap.c:80  ext4_fiemap+0x181/0x210 fs/ext4/extents.c:5051  ioctl_fiemap.isra.0+0x1b4/0x290 fs/ioctl.c:220  do_vfs_ioctl+0x31c/0x11a0 fs/ioctl.c:811  __do_sys_ioctl fs/ioctl.c:869 [inline]  __se_sys_ioctl+0xae/0x190 fs/ioctl.c:857  do_syscall_x64 arch/x86/entry/common.c:51 [inline]  do_syscall_64+0x70/0x120 arch/x86/entry/common.c:81  entry_SYSCALL_64_after_hwframe+0x78/0xe2  Allocated by task 232719:  kasan_save_stack+0x22/0x50 mm/kasan/common.c:45  kasan_set_track+0x25/0x30 mm/kasan/common.c:52  __kasan_slab_alloc+0x87/0x90 mm/kasan/common.c:328  kasan_slab_alloc include/linux/kasan.h:188 [inline]  slab_post_alloc_hook mm/slab.h:768 [inline]  slab_alloc_node mm/slub.c:3492 [inline]  kmem_cache_alloc_node+0x1b8/0x6f0 mm/slub.c:3537  bfq_get_queue+0x215/0x1f00 block/bfq-iosched.c:5869  bfq_get_bfqq_handle_split+0x167/0x5f0 block/bfq-iosched.c:6776  bfq_init_rq+0x13a4/0x17a0 block/bfq-iosched.c:6938  bfq_insert_request.isra.0+0xe8/0xa20 block/bfq-iosched.c:6271  bfq_insert_requests+0x27f/0x390 block/bfq-iosched.c:6323  blk_mq_insert_request+0x290/0x8f0 block/blk-mq.c:2660  blk_mq_submit_bio+0x1021/0x15e0 block/blk-mq.c:3143  __submit_bio+0xa0/0x6b0 block/blk-core.c:639  __submit_bio_noacct_mq block/blk-core.c:718 [inline]  submit_bio_noacct_nocheck+0x5b7/0x810 block/blk-core.c:747  submit_bio_noacct+0xca0/0x1990 block/blk-core.c:847  __ext4_read_bh fs/ext4/super.c:205 [inline]  ext4_read_bh_nowait+0x15a/0x240 fs/ext4/super.c:217  ext4_read_bh_lock+0xac/0xd0 fs/ext4/super.c:242  ext4_bread_batch+0x268/0x500 fs/ext4/inode.c:958  __ext4_find_entry+0x448/0x10f0 fs/ext4/namei.c:1671  ext4_lookup_entry fs/ext4/namei.c:1774 [inline]  ext4_lookup.part.0+0x359/0x6f0 fs/ext4/namei.c:1842  ext4_lookup+0x72/0x90 fs/ext4/namei.c:1839  __lookup_slow+0x257/0x480 fs/namei.c:1696  lookup_slow fs/namei.c:1713 [inline]  walk_component+0x454/0x5c0 fs/namei.c:2004  link_path_walk.part.0+0x773/0xda0 fs/namei.c:2331  link_path_walk fs/namei.c:3826 [inline]  path_openat+0x1b9/0x520 fs/namei.c:3826  do_filp_open+0x1b7/0x400 fs/namei.c:3857  do_sys_openat2+0x5dc/0x6e0 fs/open.c:1428  do_sys_open fs/open.c:1443 [inline]  __do_sys_openat fs/open.c:1459 [inline]  __se_sys_openat fs/open.c:1454 [inline]  __x64_sys_openat+0x148/0x200 fs/open.c:1454  do_syscall_x64 arch/x86/entry/common.c:51 [inline]  do_syscall_6 ---truncated---