High · published December 16, 2025
In the Linux kernel, the following vulnerability has been resolved:
hfs: validate record offset in hfsplus_bmap_alloc
hfsplus_bmap_alloc can trigger a crash if a
record offset or length is larger than node_size
[ 15.264282] BUG: KASAN: slab-out-of-bounds in hfsplus_bmap_alloc+0x887/0x8b0
[ 15.265192] Read of size 8 at addr ffff8881085ca188 by task test/183
[ 15.265949]
[ 15.266163] CPU: 0 UID: 0 PID: 183 Comm: test Not tainted 6.17.0-rc2-gc17b750b3ad9 #14 PREEMPT(voluntary)
[ 15.266165] Hardware name: QEMU Ubuntu 24.04 PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[ 15.266167] Call Trace:
[ 15.266168] <TASK>
[ 15.266169] dump_stack_lvl+0x53/0x70
[ 15.266173] print_report+0xd0/0x660
[ 15.266181] kasan_report+0xce/0x100
[ 15.266185] hfsplus_bmap_alloc+0x887/0x8b0
[ 15.266208] hfs_btree_inc_height.isra.0+0xd5/0x7c0
[ 15.266217] hfsplus_brec_insert+0x870/0xb00
[ 15.266222] __hfsplus_ext_write_extent+0x428/0x570
[ 15.266225] __hfsplus_ext_cache_extent+0x5e/0x910
[ 15.266227] hfsplus_ext_read_extent+0x1b2/0x200
[ 15.266233] hfsplus_file_extend+0x5a7/0x1000
[ 15.266237] hfsplus_get_block+0x12b/0x8c0
[ 15.266238] __block_write_begin_int+0x36b/0x12c0
[ 15.266251] block_write_begin+0x77/0x110
[ 15.266252] cont_write_begin+0x428/0x720
[ 15.266259] hfsplus_write_begin+0x51/0x100
[ 15.266262] cont_write_begin+0x272/0x720
[ 15.266270] hfsplus_write_begin+0x51/0x100
[ 15.266274] generic_perform_write+0x321/0x750
[ 15.266285] generic_file_write_iter+0xc3/0x310
[ 15.266289] __kernel_write_iter+0x2fd/0x800
[ 15.266296] dump_user_range+0x2ea/0x910
[ 15.266301] elf_core_dump+0x2a94/0x2ed0
[ 15.266320] vfs_coredump+0x1d85/0x45e0
[ 15.266349] get_signal+0x12e3/0x1990
[ 15.266357] arch_do_signal_or_restart+0x89/0x580
[ 15.266362] irqentry_exit_to_user_mode+0xab/0x110
[ 15.266364] asm_exc_page_fault+0x26/0x30
[ 15.266366] RIP: 0033:0x41bd35
[ 15.266367] Code: bc d1 f3 0f 7f 27 f3 0f 7f 6f 10 f3 0f 7f 77 20 f3 0f 7f 7f 30 49 83 c0 0f 49 29 d0 48 8d 7c 17 31 e9 9f 0b 00 00 66 0f ef c0 <f3> 0f 6f 0e f3 0f 6f 56 10 66 0f 74 c1 66 0f d7 d0 49 83 f8f
[ 15.266369] RSP: 002b:00007ffc9e62d078 EFLAGS: 00010283
[ 15.266371] RAX: 00007ffc9e62d100 RBX: 0000000000000000 RCX: 0000000000000000
[ 15.266372] RDX: 00000000000000e0 RSI: 0000000000000000 RDI: 00007ffc9e62d100
[ 15.266373] RBP: 0000400000000040 R08: 00000000000000e0 R09: 0000000000000000
[ 15.266374] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
[ 15.266375] R13: 0000000000000000 R14: 0000000000000000 R15: 0000400000000000
[ 15.266376] </TASK>
When calling hfsplus_bmap_alloc to allocate a free node, this function
first retrieves the bitmap from header node and map node using node->page
together with the offset and length from hfs_brec_lenoff
```
len = hfs_brec_lenoff(node, 2, &off16);
off = off16;
off += node->page_offset;
pagep = node->page + (off >> PAGE_SHIFT);
data = kmap_local_page(*pagep);
```
However, if the retrieved offset or length is invalid(i.e. exceeds
node_size), the code may end up accessing pages outside the allocated
range for this node.
This patch adds proper validation of both offset and length before use,
preventing out-of-bounds page access. Move is_bnode_offset_valid and
check_and_correct_requested_length to hfsplus_fs.h, as they may be
required by other functions.