CVE-2025-38337

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

jbd2: fix data-race and null-ptr-deref in jbd2_journal_dirty_metadata()

Since handle->h_transaction may be a NULL pointer, so we should change it to call is_handle_aborted(handle) first before dereferencing it.

And the following data-race was reported in my fuzzer:

================================================================== BUG: KCSAN: data-race in jbd2_journal_dirty_metadata / jbd2_journal_dirty_metadata

write to 0xffff888011024104 of 4 bytes by task 10881 on cpu 1: jbd2_journal_dirty_metadata+0x2a5/0x770 fs/jbd2/transaction.c:1556 __ext4_handle_dirty_metadata+0xe7/0x4b0 fs/ext4/ext4_jbd2.c:358 ext4_do_update_inode fs/ext4/inode.c:5220 [inline] ext4_mark_iloc_dirty+0x32c/0xd50 fs/ext4/inode.c:5869 __ext4_mark_inode_dirty+0xe1/0x450 fs/ext4/inode.c:6074 ext4_dirty_inode+0x98/0xc0 fs/ext4/inode.c:6103 ....

read to 0xffff888011024104 of 4 bytes by task 10880 on cpu 0: jbd2_journal_dirty_metadata+0xf2/0x770 fs/jbd2/transaction.c:1512 __ext4_handle_dirty_metadata+0xe7/0x4b0 fs/ext4/ext4_jbd2.c:358 ext4_do_update_inode fs/ext4/inode.c:5220 [inline] ext4_mark_iloc_dirty+0x32c/0xd50 fs/ext4/inode.c:5869 __ext4_mark_inode_dirty+0xe1/0x450 fs/ext4/inode.c:6074 ext4_dirty_inode+0x98/0xc0 fs/ext4/inode.c:6103 ....

value changed: 0x00000000 -> 0x00000001

This issue is caused by missing data-race annotation for jh->b_modified. Therefore, the missing annotation needs to be added.

A NULL pointer dereference and a data race condition were found in the jbd2_journal_dirty_metadata() function in the Linux kernel. The issue occurs when a transaction handle is not properly validated before dereferencing, and concurrent access to jh->b_modified is not properly synchronized. These flaws could lead to kernel crashes or memory corruption under high-concurrency conditions. The issue was reported via syzkaller and fixed by checking is_handle_aborted(handle) before accessing the transaction and adding the necessary KCSAN annotations for data race detection. This vulnerability can only be triggered by privileged users or processes with the ability to mount/ext4 filesystems and perform low-level operations that result in journal updates. Therefore, it requires CAP_SYS_ADMIN or equivalent, which justifies setting PR:H in the CVSS vector.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.