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

ext4: fix potential null deref in ext4mbinit()

In ext4mbinit(), ext4mbavgfragmentsizedestroy() may be called when sbi->smbavgfragmentsize remains uninitialized (e.g., if groupinfo slab cache allocation fails). Since ext4mbavgfragmentsizedestroy() lacks null pointer checking, this leads to a null pointer dereference.

================================================================== EXT4-fs: no memory for groupinfo slab cache BUG: kernel NULL pointer dereference, address: 0000000000000000 PGD 0 P4D 0 Oops: Oops: 0002 [#1] SMP PTI CPU:2 UID: 0 PID: 87 Comm:mount Not tainted 6.17.0-rc2 #1134 PREEMPT(none) RIP: 0010:rawspinlockirqsave+0x1b/0x40 Call Trace: <TASK> xadestroy+0x61/0x130 ext4mbinit+0x483/0x540 _ext4fillsuper+0x116d/0x17b0 ext4fillsuper+0xd3/0x280 gettreebdevflags+0x132/0x1d0 vfsgettree+0x29/0xd0 donewmount+0x197/0x300 _x64sysmount+0x116/0x150 dosyscall64+0x50/0x1c0

entrySYSCALL64afterhwframe+0x76/0x7e

Therefore, add necessary null check to ext4mbavgfragmentsizedestroy() to prevent this issue. The same fix is also applied to ext4mblargestfreeordersdestroy().