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

ext4: fix bug_on in __estreesearch caused by bad boot loader inode

We got a issue as fllows:

kernel BUG at fs/ext4/extentsstatus.c:203! invalid opcode: 0000 [#1] PREEMPT SMP CPU: 1 PID: 945 Comm: cat Not tainted 6.0.0-next-20221007-dirty #349 RIP: 0010:ext4es_end.isra.0+0x34/0x42 RSP: 0018:ffffc9000143b768 EFLAGS: 00010203 RAX: 0000000000000000 RBX: ffff8881769cd0b8 RCX: 0000000000000000 RDX: 0000000000000000 RSI: ffffffff8fc27cf7 RDI: 00000000ffffffff RBP: ffff8881769cd0bc R08: 0000000000000000 R09: ffffc9000143b5f8 R10: 0000000000000001 R11: 0000000000000001 R12: ffff8881769cd0a0 R13: ffff8881768e5668 R14: 00000000768e52f0 R15: 0000000000000000 FS: 00007f359f7f05c0(0000)GS:ffff88842fd00000(0000)knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f359f5a2000 CR3: 000000017130c000 CR4: 00000000000006e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: <TASK> __estreesearch.isra.0+0x6d/0xf5 ext4escacheextent+0xfa/0x230 ext4cacheextents+0xd2/0x110 ext4findextent+0x5d5/0x8c0 ext4extmapblocks+0x9c/0x1d30 ext4mapblocks+0x431/0xa50 ext4mpagereadpages+0x48e/0xe40 ext4readahead+0x47/0x50 readpages+0x82/0x530 pagecacheraunbounded+0x199/0x2a0 dopagecachera+0x47/0x70 pagecacheraorder+0x242/0x400 ondemandreadahead+0x1e8/0x4b0 pagecachesyncra+0xf4/0x110 filemapgetpages+0x131/0xb20 filemapread+0xda/0x4b0 genericfilereaditer+0x13a/0x250 ext4filereaditer+0x59/0x1d0 vfsread+0x28f/0x460 ksysread+0x73/0x160 __x64sysread+0x1e/0x30 dosyscall64+0x35/0x80 entrySYSCALL64afterhwframe+0x63/0xcd

</TASK>

In the above issue, ioctl invokes the swapinodebootloader function to swap inode<5> and inode<12>. However, inode<5> contain incorrect imode and disordered extents, and inlink is set to 1. The extents check for inode in the ext4iget function can be bypassed bacause 5 is EXT4BOOTLOADERINO. While linkscount is set to 1, the extents are not initialized in swapinodebootloader. After the ioctl command is executed successfully, the extents are swapped to inode<12>, in this case, run the cat command to view inode<12>. And Bug_ON is triggered due to the incorrect extents.

When the boot loader inode is not initialized, its imode can be one of the following: 1) the imode is a bad type, which is marked as badinode in ext4iget and set to SIFREG. 2) the imode is good type but not SIFREG. 3) the imode is S_IFREG.

The BUGON may be triggered by bypassing the check in cases 1 and 2. Therefore, when the boot loader inode is badinode or its imode is not S_IFREG, initialize the inode to avoid triggering the BUG.