isofs: Prevent the use of too small fid

Summary

In the Linux kernel, the following vulnerability has been resolved: isofs: Prevent the use of too small fid syzbot reported a slab-out-of-bounds Read in isofs_fh_to_parent. [1] The handle_bytes value passed in by the reproducing program is equal to 12. In handle_to_path(), only 12 bytes of memory are allocated for the structure file_handle->f_handle member, which causes an out-of-bounds access when accessing the member parent_block of the structure isofs_fid in isofs, because accessing parent_block requires at least 16 bytes of f_handle. Here, fh_len is used to indirectly confirm that the value of handle_bytes is greater than 3 before accessing parent_block. [1] BUG: KASAN: slab-out-of-bounds in isofs_fh_to_parent+0x1b8/0x210 fs/isofs/export.c:183 Read of size 4 at addr ffff0000cc030d94 by task syz-executor215/6466 CPU: 1 UID: 0 PID: 6466 Comm: syz-executor215 Not tainted 6.14.0-rc7-syzkaller-ga2392f333575 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025 Call trace: show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:466 (C) __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0xe4/0x150 lib/dump_stack.c:120 print_address_description mm/kasan/report.c:408 [inline] print_report+0x198/0x550 mm/kasan/report.c:521 kasan_report+0xd8/0x138 mm/kasan/report.c:634 __asan_report_load4_noabort+0x20/0x2c mm/kasan/report_generic.c:380 isofs_fh_to_parent+0x1b8/0x210 fs/isofs/export.c:183 exportfs_decode_fh_raw+0x2dc/0x608 fs/exportfs/expfs.c:523 do_handle_to_path+0xa0/0x198 fs/fhandle.c:257 handle_to_path fs/fhandle.c:385 [inline] do_handle_open+0x8cc/0xb8c fs/fhandle.c:403 __do_sys_open_by_handle_at fs/fhandle.c:443 [inline] __se_sys_open_by_handle_at fs/fhandle.c:434 [inline] __arm64_sys_open_by_handle_at+0x80/0x94 fs/fhandle.c:434 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline] invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:49 el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132 do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151 el0_svc+0x54/0x168 arch/arm64/kernel/entry-common.c:744 el0t_64_sync_handler+0x84/0x108 arch/arm64/kernel/entry-common.c:762 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:600 Allocated by task 6466: kasan_save_stack mm/kasan/common.c:47 [inline] kasan_save_track+0x40/0x78 mm/kasan/common.c:68 kasan_save_alloc_info+0x40/0x50 mm/kasan/generic.c:562 poison_kmalloc_redzone mm/kasan/common.c:377 [inline] __kasan_kmalloc+0xac/0xc4 mm/kasan/common.c:394 kasan_kmalloc include/linux/kasan.h:260 [inline] __do_kmalloc_node mm/slub.c:4294 [inline] __kmalloc_noprof+0x32c/0x54c mm/slub.c:4306 kmalloc_noprof include/linux/slab.h:905 [inline] handle_to_path fs/fhandle.c:357 [inline] do_handle_open+0x5a4/0xb8c fs/fhandle.c:403 __do_sys_open_by_handle_at fs/fhandle.c:443 [inline] __se_sys_open_by_handle_at fs/fhandle.c:434 [inline] __arm64_sys_open_by_handle_at+0x80/0x94 fs/fhandle.c:434 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline] invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:49 el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132 do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151 el0_svc+0x54/0x168 arch/arm64/kernel/entry-common.c:744 el0t_64_sync_handler+0x84/0x108 arch/arm64/kernel/entry-common.c:762 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:600