🇰🇷 한글 설명
Linux 커널의 forcedeth 드라이버에서 비-PCI 설정 공간을 저장하고 복구할 때 발생하는 off-by-one 오류입니다. 루프 조건문 오류로 인해 배열의 범위를 벗어난 메모리에 접근하며, 이는 UBSAN에 의해 탐지되어 커널 트랩을 발생시키거나 잘못된 MMIO 읽기/쓰기를 유발할 수 있습니다.
💡 쉬운 설명
컴퓨터 부품을 관리하는 프로그램이 데이터를 저장할 때 정해진 칸보다 하나 더 많은 칸을 건드리는 실수입니다. 이로 인해 시스템이 갑자기 멈추거나 예상치 못한 동작을 할 수 있습니다.
🇺🇸 원문 (English)
In the Linux kernel, the following vulnerability has been resolved:
forcedeth: fix off-by-one when saving/restoring non-PCI config space
nv_suspend() and nv_resume() walk the non-PCI configuration space with
for (i = 0; i <= np->register_size/sizeof(u32); i++)
which runs one iteration too many. saved_config_space is declared as
u32 saved_config_space[NV_PCI_REGSZ_MAX/4];
and NV_PCI_REGSZ_VER3 is equal to NV_PCI_REGSZ_MAX (0x604), so on a VER3
device register_size/sizeof(u32) is exactly the array length and the last
iteration addresses one element past the end.
The element it lands on is np->name_rx[0..3]: saved_config_space[] is
followed immediately by char name_rx[IFNAMSIZ + 3], and char needs no
padding. Nothing observable is corrupted by that, because nv_request_irq()
rewrites name_rx with sprintf() before it is ever passed to request_irq().
The bug is the out-of-bounds access itself, which UBSAN reports and which
CONFIG_UBSAN_TRAP=y turns into a trap that aborts the running kernel code,
plus an MMIO read and, on resume, an MMIO writel() to base + 0x604, one
dword past the range the driver mapped:
np->base = ioremap(addr, np->register_size);
VER1 and VER2 devices stay inside the array, but they too get the stray
read and the stray write one dword past their own window.
Caught by UBSAN on an Apple Macmini3,1 (MCP79) during a deep S3 cycle.
The splat below is trimmed: the build path in the file name, the CPU
and taint lines, the Workqueue line, the "?" hint frames, and the
frames below device_suspend are all cut. The kernel was tainted, with
an out-of-tree nouveau and CPU_OUT_OF_SPEC; forcedeth itself was the
stock module.
UBSAN: array-index-out-of-bounds in drivers/net/ethernet/nvidia/forcedeth.c:6225:25
index 385 is out of range for type 'u32 [385]'
Call Trace:
dump_stack_lvl+0x5d/0x80
ubsan_epilogue+0x5/0x2b
__ubsan_handle_out_of_bounds.cold+0x54/0x59
__this_module+0xe398c/0xe9010 [forcedeth]
pci_pm_suspend+0x80/0x170
dpm_run_callback+0x51/0x160
device_suspend+0x1a2/0x4a0
...
Both loops are hit. UBSAN reports each source location only once per module
load (__ubsan_handle_out_of_bounds() calls suppress_report(), which does
test_and_set_bit(REPORTED_BIT, ...) on the struct source_location), so the
two splats land in the first S3 cycle after the module is loaded and later
cycles are silent even though the access still runs off the end every time.
In that first cycle line 6225 is reported from pci_pm_suspend and line 6240
from pci_pm_resume.
The same off-by-one was fixed in nv_get_regs() by commit ba9aa134287f
("forcedeth: fix buffer overflow") in 2012; these two loops were missed.
The suspend and resume side was reported on LKML in September 2013 by Marc
Weber, with the same analysis and the same one-character fix, but the patch
was attached rather than sent inline and the thread ended there.
Use < instead of <=, which saves and restores exactly register_size bytes.
📍 영향받는 시스템
Linux kernel (forcedeth driver 사용 시스템)
⚔️ 공격 벡터
로컬 공격자가 시스템의 절전 모드(S3) 진입/해제를 유도하여 커널 패닉 또는 메모리 오염 유발
🛡️ 대응 방법
커널 소스 코드의 forcedeth 드라이버 내 루프 조건문을 '<='에서 '<'로 수정하여 패치 적용
🔧 검증 코드
출력된 커널 버전이 해당 취약점이 패치된 최신 보안 업데이트 버전인지 확인합니다.