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

Vulnerability Description

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 We should guarantee the timer is no longer active before kfree(sbi).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.

References

• https://git.kernel.org/stable/c/7aac0c17a8cdf4a3236991c1e60435c6a984076c
• https://git.kernel.org/stable/c/22e9b83f0f33bc5a7a3181769d1dccbf021f5b04
• https://git.kernel.org/stable/c/cf3196e5e2f36cd80dab91ffae402e13935724bc
• https://git.kernel.org/stable/c/9203817ba46ebba7c865c8de2aba399537b6e891
• https://git.kernel.org/stable/c/fa78fb51d396f4f2f80f8e96a3b1516f394258be
• https://git.kernel.org/stable/c/b85569585d0154d4db1e4f9e3e6a4731d407feb0
• https://git.kernel.org/stable/c/0ce160c5bdb67081a62293028dc85758a8efb22a