Hello,
The following program causes heap-of-bounds access in array_map_update_elem: // autogenerated by syzkaller (http://github.com/google/syzkaller) #include <syscall.h> #include <string.h> #include <stdint.h> #define SYS_bpf 321 int main() { long r0 = syscall(SYS_mmap, 0x20000000ul, 0x10000ul, 0x3ul, 0x32ul, 0xfffffffffffffffful, 0x0ul); *(uint32_t*)0x20000d9b = 0x2; *(uint32_t*)0x20000d9f = 0x4; *(uint32_t*)0x20000da3 = 0x7; *(uint32_t*)0x20000da7 = 0x9; long r5 = syscall(SYS_bpf, 0x0ul, 0x20000d9bul, 0x10ul, 0, 0, 0); *(uint32_t*)0x20001fe0 = r5; *(uint32_t*)0x20001fe4 = 0x0; *(uint64_t*)0x20001fe8 = 0x20001000; *(uint64_t*)0x20001ff0 = 0x20000f42; *(uint64_t*)0x20001ff8 = 0x0; long r11 = syscall(SYS_bpf, 0x2ul, 0x20001fe0ul, 0x20ul, 0, 0, 0); *(uint32_t*)0x20001fe0 = r5; *(uint32_t*)0x20001fe4 = 0x0; *(uint64_t*)0x20001fe8 = 0x20001000; *(uint64_t*)0x20001ff0 = 0x20000f42; *(uint64_t*)0x20001ff8 = 0x0; long r17 = syscall(SYS_bpf, 0x2ul, 0x20001fe0ul, 0x20ul, 0, 0, 0); return 0; } ================================================================== BUG: KASAN: slab-out-of-bounds in memcpy+0x1d/0x40 at addr ffff88003a6bd110 Read of size 8 by task a.out/6260 ============================================================================= BUG kmalloc-8 (Tainted: G B ): kasan: bad access detected ----------------------------------------------------------------------------- INFO: Allocated in SyS_bpf+0xfd4/0x1a20 age=4 cpu=0 pid=6260 [< none >] __slab_alloc+0x235/0x570 mm/slub.c:2399 [< inline >] slab_alloc_node mm/slub.c:2467 [< inline >] slab_alloc mm/slub.c:2509 [< none >] __kmalloc+0x1f7/0x260 mm/slub.c:3414 [< inline >] kmalloc include/linux/slab.h:445 [< inline >] map_update_elem kernel/bpf/syscall.c:288 [< inline >] SYSC_bpf kernel/bpf/syscall.c:744 [< none >] SyS_bpf+0xfd4/0x1a20 kernel/bpf/syscall.c:695 [< none >] entry_SYSCALL_64_fastpath+0x16/0x7a arch/x86/entry/entry_64.S:185 INFO: Slab 0xffffea0000e9af00 objects=24 used=14 fp=0xffff88003a6bd3b0 flags=0x1fffc0000004080 INFO: Object 0xffff88003a6bd110 @offset=4368 fp=0xffff88003a6bc930 CPU: 0 PID: 6260 Comm: a.out Tainted: G B 4.4.0-rc1+ #129 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 00000000ffffffff ffff880033347ce0 ffffffff82745526 ffff88003e804280 ffff88003a6bd110 ffff88003a6bc000 ffff880033347d10 ffffffff816229c4 ffff88003e804280 ffffea0000e9af00 ffff88003a6bd110 0000000000000000 Call Trace: [<ffffffff8162a294>] __asan_loadN+0x124/0x1a0 mm/kasan/kasan.c:510 [<ffffffff8162a81d>] memcpy+0x1d/0x40 mm/kasan/kasan.c:296 [<ffffffff814fd66a>] array_map_update_elem+0xca/0x110 kernel/bpf/arraymap.c:108 [< inline >] map_update_elem kernel/bpf/syscall.c:300 [< inline >] SYSC_bpf kernel/bpf/syscall.c:744 [<ffffffff814efa89>] SyS_bpf+0x1509/0x1a20 kernel/bpf/syscall.c:695 [<ffffffff85988836>] entry_SYSCALL_64_fastpath+0x16/0x7a arch/x86/entry/entry_64.S:185 ================================================================== On commit 90b55590c43258a157a2a143748455dcc50fbb53 (Nov 20). The OOB accesses happens here: static int array_map_update_elem(struct bpf_map *map, void *key, void *value, u64 map_flags) { .... memcpy(array->value + array->elem_size * index, value, array->elem_size); Memory allocated for value is of size array->value_size, which can be up to 7 bytes less than array->elem_size. Most likely it cannot lead to GPF when called from syscall with current slab implementation. I don't know whether this OOB can cause any issues when called from a BPF program. It also copies uninit garbage into the map. I don't see how that garbage can be fetched later either by syscall or by a BPF program. But still I think it is better to copy array->elem_size and leave the trailer zero initialized just to be on the safer side. Thanks -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
