How to: CVE-2025-39866 (2025-09-19)
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In the Linux kernel, the following vulnerability has been resolved:\n\nfs: writeback: fix use-after-free in __mark_inode_dirty()\n\nAn use-after-free issue occurred when __mark_inode_dirty() get the\nbdi_writeback that was in the progress of switching.\n\nCPU: 1 PID: 562 Comm: systemd-random- Not tainted 6.6.56-gb4403bd46a8e #1\n......\npstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)\npc : __mark_inode_dirty+0x124/0x418\nlr : __mark_inode_dirty+0x118/0x418\nsp : ffffffc08c9dbbc0\n........\nCall trace:\n __mark_inode_dirty+0x124/0x418\n generic_update_time+0x4c/0x60\n file_modified+0xcc/0xd0\n ext4_buffered_write_iter+0x58/0x124\n ext4_file_write_iter+0x54/0x704\n vfs_write+0x1c0/0x308\n ksys_write+0x74/0x10c\n __arm64_sys_write+0x1c/0x28\n invoke_syscall+0x48/0x114\n el0_svc_common.constprop.0+0xc0/0xe0\n do_el0_svc+0x1c/0x28\n el0_svc+0x40/0xe4\n el0t_64_sync_handler+0x120/0x12c\n el0t_64_sync+0x194/0x198\n\nRoot cause is:\n\nsystemd-random-seed                         kworker\n----------------------------------------------------------------------\n___mark_inode_dirty                     inode_switch_wbs_work_fn\n\n  spin_lock(&inode->i_lock);\n  inode_attach_wb\n  locked_inode_to_wb_and_lock_list\n     get inode->i_wb\n     spin_unlock(&inode->i_lock);\n     spin_lock(&wb->list_lock)\n  spin_lock(&inode->i_lock)\n  inode_io_list_move_locked\n  spin_unlock(&wb->list_lock)\n  spin_unlock(&inode->i_lock)\n                                    spin_lock(&old_wb->list_lock)\n                                      inode_do_switch_wbs\n                                        spin_lock(&inode->i_lock)\n                                        inode->i_wb = new_wb\n                                        spin_unlock(&inode->i_lock)\n                                    spin_unlock(&old_wb->list_lock)\n                                    wb_put_many(old_wb, nr_switched)\n                                      cgwb_release\n                                      old wb released\n  wb_wakeup_delayed() accesses wb,\n  then trigger the use-after-free\n  issue\n\nFix this race condition by holding inode spinlock until\nwb_wakeup_delayed() finished.
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- [byteReaper77/CVE-2025-39866](https://github.com/byteReaper77/CVE-2025-39866)