CVE-2024-56686 Information

Description

In the Linux kernel the following vulnerability has been resolved:

ext4: fix race in buffer_head read fault injection

When I enabled ext4 debug for fault injection testing I encountered the following warning:

EXT4-fs error (device sda): ext4_read_inode_bitmap:201: comm fsstress: Cannot read inode bitmap - block_group = 8 inode_bitmap = 1051 WARNING: CPU: 0 PID: 511 at fs/buffer.c:1181 mark_buffer_dirty+0x1b3/0x1d0

The root cause of the issue lies in the improper implementation of ext4’s buffer_head read fault injection. The actual completion of buffer_head read and the buffer_head fault injection are not atomic which can lead to the uptodate flag being cleared on normally used buffer_heads in race conditions.

[CPU0] [CPU1] [CPU2] ext4_read_inode_bitmap ext4_read_bh() ext4_read_inode_bitmap if (buffer_uptodate(bh)) return bh jbd2_journal_commit_transaction __jbd2_journal_refile_buffer __jbd2_journal_unfile_buffer __jbd2_journal_temp_unlink_buffer ext4_simulate_fail_bh() clear_buffer_uptodate mark_buffer_dirty WARN_ON_ONCE(!buffer_uptodate(bh))

The best approach would be to perform fault injection in the IO completion callback function rather than after IO completion. However the IO completion callback function cannot get the fault injection code in sb.

Fix it by passing the result of fault injection into the bh read function we simulate faults within the bh read function itself. This requires adding an extra parameter to the bh read functions that need fault injection.

Reference

https://git.kernel.org/stable/c/25a5acf88fed59e060405bbb48098f4a3a2c2adc https://git.kernel.org/stable/c/2f3d93e210b9c2866c8b3662adae427d5bf511ec https://git.kernel.org/stable/c/61832ee7fa2fbd569d129379e795038abfb0d128 https://git.kernel.org/stable/c/77035e4d27e15f87ea55929c8bb8fb1970129e2f