CVE-2025-39866

In the Linux kernel, the following vulnerability has been resolved:

fs: writeback: fix use-after-free in __mark_inode_dirty()

An use-after-free issue occurred when __mark_inode_dirty() get the bdi_writeback that was in the progress of switching.

CPU: 1 PID: 562 Comm: systemd-random- Not tainted 6.6.56-gb4403bd46a8e #1 …… pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=–) pc : __mark_inode_dirty+0x124/0x418 lr : __mark_inode_dirty+0x118/0x418 sp : ffffffc08c9dbbc0 …….. Call trace: __mark_inode_dirty+0x124/0x418 generic_update_time+0x4c/0x60 file_modified+0xcc/0xd0 ext4_buffered_write_iter+0x58/0x124 ext4_file_write_iter+0x54/0x704 vfs_write+0x1c0/0x308 ksys_write+0x74/0x10c __arm64_sys_write+0x1c/0x28 invoke_syscall+0x48/0x114 el0_svc_common.constprop.0+0xc0/0xe0 do_el0_svc+0x1c/0x28 el0_svc+0x40/0xe4 el0t_64_sync_handler+0x120/0x12c el0t_64_sync+0x194/0x198

Root cause is:

systemd-random-seed kworker

___mark_inode_dirty inode_switch_wbs_work_fn

spin_lock(&inode->i_lock); inode_attach_wb locked_inode_to_wb_and_lock_list get inode->i_wb spin_unlock(&inode->i_lock); spin_lock(&wb->list_lock) spin_lock(&inode->i_lock) inode_io_list_move_locked spin_unlock(&wb->list_lock) spin_unlock(&inode->i_lock) spin_lock(&old_wb->list_lock) inode_do_switch_wbs spin_lock(&inode->i_lock) inode->i_wb = new_wb spin_unlock(&inode->i_lock) spin_unlock(&old_wb->list_lock) wb_put_many(old_wb, nr_switched) cgwb_release old wb released wb_wakeup_delayed() accesses wb, then trigger the use-after-free issue

Fix this race condition by holding inode spinlock until wb_wakeup_delayed() finished.

Affected Software

References

• https://git.kernel.org/stable/c/1edc2feb9c759a9883dfe81cb5ed231412d8b2e4
• https://git.kernel.org/stable/c/b187c976111960e6e54a6b1fff724f6e3d39406c
• https://git.kernel.org/stable/c/bf89b1f87c72df79cf76203f71fbf8349cd5c9de
• https://git.kernel.org/stable/c/c8c14adf80bd1a6e4a1d7ee9c2a816881c26d17a
• https://git.kernel.org/stable/c/d02d2c98d25793902f65803ab853b592c7a96b29
• https://git.kernel.org/stable/c/e63052921f1b25a836feb1500b841bff7a4a0456