5.10-stable review patch. If anyone has any objections, please let me know.
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From: Jiufei Xue jiufei.xue@samsung.com
[ Upstream commit d02d2c98d25793902f65803ab853b592c7a96b29 ]
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.
Signed-off-by: Jiufei Xue jiufei.xue@samsung.com Link: https://lore.kernel.org/20250728100715.3863241-1-jiufei.xue@samsung.com Reviewed-by: Jan Kara jack@suse.cz Signed-off-by: Christian Brauner brauner@kernel.org Signed-off-by: Nazar Kalashnikov sivartiwe@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- Backport fix for CVE-2025-39866 fs/fs-writeback.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)
--- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -2326,9 +2326,6 @@ void __mark_inode_dirty(struct inode *in wakeup_bdi = inode_io_list_move_locked(inode, wb, dirty_list);
- spin_unlock(&wb->list_lock); - trace_writeback_dirty_inode_enqueue(inode); - /* * If this is the first dirty inode for this bdi, * we have to wake-up the corresponding bdi thread @@ -2338,6 +2335,10 @@ void __mark_inode_dirty(struct inode *in if (wakeup_bdi && (wb->bdi->capabilities & BDI_CAP_WRITEBACK)) wb_wakeup_delayed(wb); + + spin_unlock(&wb->list_lock); + trace_writeback_dirty_inode_enqueue(inode); + return; } }