CVE-2026-74426: afs: fix NULL pointer dereference in afs_get_tree()

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

afs: fix NULL pointer dereference in afsgettree()

afsallocsbi() uses kzalloc for memory allocation. And, if ctx->dynroot is not null, as->cell and as->volume are null. In traceafsgettree() they are dereferenced.

KASAN error message:

KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] CPU: 2 PID: 18478 Comm: syz-executor.7 Not tainted 5.10.246-syzkaller #0 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014 RIP: 0010:perftraceafsgettree+0x1d9/0x550 include/trace/events/afs.h:1365

Call Trace: traceafsgettree include/trace/events/afs.h:1365 [inline] afsgettree+0x922/0x1350 fs/afs/super.c:599 vfsgettree+0x8e/0x300 fs/super.c:1572 donewmount fs/namespace.c:3011 [inline] pathmount+0x14a5/0x2220 fs/namespace.c:3341 domount fs/namespace.c:3354 [inline] dosysmount fs/namespace.c:3562 [inline] sesysmount fs/namespace.c:3539 [inline] x64sysmount+0x283/0x300 fs/namespace.c:3539 dosyscall64+0x33/0x50 arch/x86/entry/common.c:46 entrySYSCALL64afterhwframe+0x67/0xd1

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.