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

ext4: move ext4percpuparaminit() before ext4mb_init()

When running kvm-xfstests -c ext4/1k -C 1 generic/383 with the DOUBLE_CHECK macro defined, the following panic is triggered:

================================================================== EXT4-fs error (device vdc): ext4validateblockbitmap:423: comm mount: bg 0: bad block bitmap checksum BUG: unable to handle page fault for address: ff110000fa2cc000 PGD 3e01067 P4D 3e02067 PUD 0 Oops: Oops: 0000 [#1] SMP NOPTI CPU: 0 UID: 0 PID: 2386 Comm: mount Tainted: G W 6.18.0-gba65a4e7120a-dirty #1152 PREEMPT(none) RIP: 0010:percpucounteraddbatch+0x13/0xa0 Call Trace: <TASK> ext4markgroupbitmapcorrupted+0xcb/0xe0 ext4validateblockbitmap+0x2a1/0x2f0 ext4readblockbitmap+0x33/0x50 mbgroupbbbitmapalloc+0x33/0x80 ext4mbaddgroupinfo+0x190/0x250 ext4mbinitbackend+0x87/0x290 ext4mbinit+0x456/0x640 __ext4fillsuper+0x1072/0x1680 ext4_fillsuper+0xd3/0x280 gettreebdevflags+0x132/0x1d0 vfsgettree+0x29/0xd0 vfscmdcreate+0x59/0xe0 __dosysfsconfig+0x4f6/0x6b0 dosyscall64+0x50/0x1f0

entrySYSCALL64afterhwframe+0x76/0x7e

This issue can be reproduced using the following commands: mkfs.ext4 -F -q -b 1024 /dev/sda 5G tune2fs -O quota,project /dev/sda mount /dev/sda /tmp/test

With DOUBLECHECK defined, mbgroupbbbitmapalloc() reads and validates the block bitmap. When the validation fails, ext4markgroupbitmapcorrupted() attempts to update sbi->sfreeclusterscounter. However, this percpucounter has not been initialized yet at this point, which leads to the panic described above.

Fix this by moving the execution of ext4percpuparaminit() to occur before ext4mb_init(), ensuring the per-CPU counters are initialized before they are used.