Affected: Linux

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

ext4: fix timer use-after-free on failed mount

Syzbot has found an ODEBUG bug in ext4_fill_super

The del_timer_sync function cancels the s_err_report timer, which reminds about filesystem errors daily. We should guarantee the timer is no longer active before kfree(sbi).

When filesystem mounting fails, the flow goes to failed_mount3, where an error occurs when ext4_stop_mmpd is called, causing a read I/O failure. This triggers the ext4_handle_error function that ultimately re-arms the timer, leaving the s_err_report timer active before kfree(sbi) is called.

Fix the issue by canceling the s_err_report timer after calling ext4_stop_mmpd.