CVE-2025-21753

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> btrfs: fix use-after-free when attempting to join an aborted transaction<br /> <br /> When we are trying to join the current transaction and if it&amp;#39;s aborted,<br /> we read its &amp;#39;aborted&amp;#39; field after unlocking fs_info-&gt;trans_lock and<br /> without holding any extra reference count on it. This means that a<br /> concurrent task that is aborting the transaction may free the transaction<br /> before we read its &amp;#39;aborted&amp;#39; field, leading to a use-after-free.<br /> <br /> Fix this by reading the &amp;#39;aborted&amp;#39; field while holding fs_info-&gt;trans_lock<br /> since any freeing task must first acquire that lock and set<br /> fs_info-&gt;running_transaction to NULL before freeing the transaction.<br /> <br /> This was reported by syzbot and Dmitry with the following stack traces<br /> from KASAN:<br /> <br /> ==================================================================<br /> BUG: KASAN: slab-use-after-free in join_transaction+0xd9b/0xda0 fs/btrfs/transaction.c:278<br /> Read of size 4 at addr ffff888011839024 by task kworker/u4:9/1128<br /> <br /> CPU: 0 UID: 0 PID: 1128 Comm: kworker/u4:9 Not tainted 6.13.0-rc7-syzkaller-00019-gc45323b7560e #0<br /> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014<br /> Workqueue: events_unbound btrfs_async_reclaim_data_space<br /> Call Trace:<br /> <br /> __dump_stack lib/dump_stack.c:94 [inline]<br /> dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120<br /> print_address_description mm/kasan/report.c:378 [inline]<br /> print_report+0x169/0x550 mm/kasan/report.c:489<br /> kasan_report+0x143/0x180 mm/kasan/report.c:602<br /> join_transaction+0xd9b/0xda0 fs/btrfs/transaction.c:278<br /> start_transaction+0xaf8/0x1670 fs/btrfs/transaction.c:697<br /> flush_space+0x448/0xcf0 fs/btrfs/space-info.c:803<br /> btrfs_async_reclaim_data_space+0x159/0x510 fs/btrfs/space-info.c:1321<br /> process_one_work kernel/workqueue.c:3236 [inline]<br /> process_scheduled_works+0xa66/0x1840 kernel/workqueue.c:3317<br /> worker_thread+0x870/0xd30 kernel/workqueue.c:3398<br /> kthread+0x2f0/0x390 kernel/kthread.c:389<br /> ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147<br /> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244<br /> <br /> <br /> Allocated by task 5315:<br /> kasan_save_stack mm/kasan/common.c:47 [inline]<br /> kasan_save_track+0x3f/0x80 mm/kasan/common.c:68<br /> poison_kmalloc_redzone mm/kasan/common.c:377 [inline]<br /> __kasan_kmalloc+0x98/0xb0 mm/kasan/common.c:394<br /> kasan_kmalloc include/linux/kasan.h:260 [inline]<br /> __kmalloc_cache_noprof+0x243/0x390 mm/slub.c:4329<br /> kmalloc_noprof include/linux/slab.h:901 [inline]<br /> join_transaction+0x144/0xda0 fs/btrfs/transaction.c:308<br /> start_transaction+0xaf8/0x1670 fs/btrfs/transaction.c:697<br /> btrfs_create_common+0x1b2/0x2e0 fs/btrfs/inode.c:6572<br /> lookup_open fs/namei.c:3649 [inline]<br /> open_last_lookups fs/namei.c:3748 [inline]<br /> path_openat+0x1c03/0x3590 fs/namei.c:3984<br /> do_filp_open+0x27f/0x4e0 fs/namei.c:4014<br /> do_sys_openat2+0x13e/0x1d0 fs/open.c:1402<br /> do_sys_open fs/open.c:1417 [inline]<br /> __do_sys_creat fs/open.c:1495 [inline]<br /> __se_sys_creat fs/open.c:1489 [inline]<br /> __x64_sys_creat+0x123/0x170 fs/open.c:1489<br /> do_syscall_x64 arch/x86/entry/common.c:52 [inline]<br /> do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83<br /> entry_SYSCALL_64_after_hwframe+0x77/0x7f<br /> <br /> Freed by task 5336:<br /> kasan_save_stack mm/kasan/common.c:47 [inline]<br /> kasan_save_track+0x3f/0x80 mm/kasan/common.c:68<br /> kasan_save_free_info+0x40/0x50 mm/kasan/generic.c:582<br /> poison_slab_object mm/kasan/common.c:247 [inline]<br /> __kasan_slab_free+0x59/0x70 mm/kasan/common.c:264<br /> kasan_slab_free include/linux/kasan.h:233 [inline]<br /> slab_free_hook mm/slub.c:2353 [inline]<br /> slab_free mm/slub.c:4613 [inline]<br /> kfree+0x196/0x430 mm/slub.c:4761<br /> cleanup_transaction fs/btrfs/transaction.c:2063 [inline]<br /> btrfs_commit_transaction+0x2c97/0x3720 fs/btrfs/transaction.c:2598<br /> insert_balance_item+0x1284/0x20b0 fs/btrfs/volumes.c:3757<br /> btrfs_balance+0x992/<br /> ---truncated---