Commit 17605c5c authored by Yonghong Song's avatar Yonghong Song Committed by Chen Zhongjin
Browse files

bpf: Fail verification for sign-extension of packet data/data_end/data_meta 

mainline inclusion
from mainline-v6.12-rc1
commit 92de36080c93296ef9005690705cba260b9bd68a
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/IAYPJQ
CVE: CVE-2024-47702

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=92de36080c93296ef9005690705cba260b9bd68a

--------------------------------

syzbot reported a kernel crash due to
  commit 1f1e864b ("bpf: Handle sign-extenstin ctx member accesses").
The reason is due to sign-extension of 32-bit load for
packet data/data_end/data_meta uapi field.

The original code looks like:
        r2 = *(s32 *)(r1 + 76) /* load __sk_buff->data */
        r3 = *(u32 *)(r1 + 80) /* load __sk_buff->data_end */
        r0 = r2
        r0 += 8
        if r3 > r0 goto +1
        ...
Note that __sk_buff->data load has 32-bit sign extension.

After verification and convert_ctx_accesses(), the final asm code looks like:
        r2 = *(u64 *)(r1 +208)
        r2 = (s32)r2
        r3 = *(u64 *)(r1 +80)
        r0 = r2
        r0 += 8
        if r3 > r0 goto pc+1
        ...
Note that 'r2 = (s32)r2' may make the kernel __sk_buff->data address invalid
which may cause runtime failure.

Currently, in C code, typically we have
        void *data = (void *)(long)skb->data;
        void *data_end = (void *)(long)skb->data_end;
        ...
and it will generate
        r2 = *(u64 *)(r1 +208)
        r3 = *(u64 *)(r1 +80)
        r0 = r2
        r0 += 8
        if r3 > r0 goto pc+1

If we allow sign-extension,
        void *data = (void *)(long)(int)skb->data;
        void *data_end = (void *)(long)skb->data_end;
        ...
the generated code looks like
        r2 = *(u64 *)(r1 +208)
        r2 <<= 32
        r2 s>>= 32
        r3 = *(u64 *)(r1 +80)
        r0 = r2
        r0 += 8
        if r3 > r0 goto pc+1
and this will cause verification failure since "r2 <<= 32" is not allowed
as "r2" is a packet pointer.

To fix this issue for case
  r2 = *(s32 *)(r1 + 76) /* load __sk_buff->data */
this patch added additional checking in is_valid_access() callback
function for packet data/data_end/data_meta access. If those accesses
are with sign-extenstion, the verification will fail.

  [1] https://lore.kernel.org/bpf/000000000000c90eee061d236d37@google.com/



Reported-by: default avatar <syzbot+ad9ec60c8eaf69e6f99c@syzkaller.appspotmail.com>
Fixes: 1f1e864b ("bpf: Handle sign-extenstin ctx member accesses")
Acked-by: default avatarEduard Zingerman <eddyz87@gmail.com>
Signed-off-by: default avatarYonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20240723153439.2429035-1-yonghong.song@linux.dev


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Conflicts:
	include/linux/bpf.h
[fix context change in struct bpf_insn_access_aux]
Signed-off-by: default avatarChen Zhongjin <chenzhongjin@huawei.com>
parent be251396

include/linux/bpf.h

+1 −0
Original line number Diff line number Diff line
@@ -914,6 +914,7 @@ static_assert(__BPF_REG_TYPE_MAX <= BPF_BASE_TYPE_LIMIT); 
struct bpf_insn_access_aux {

	enum bpf_reg_type reg_type;

	KABI_FILL_HOLE(bool is_retval) /* is accessing function return value ? */

	bool is_ldsx;

	union {

		int ctx_field_size;

		struct {

kernel/bpf/verifier.c

+3 −2
Original line number Diff line number Diff line
@@ -5576,12 +5576,13 @@ static int check_packet_access(struct bpf_verifier_env *env, u32 regno, int off, 
/* check access to 'struct bpf_context' fields.  Supports fixed offsets only */

static int check_ctx_access(struct bpf_verifier_env *env, int insn_idx, int off, int size,

			    enum bpf_access_type t, enum bpf_reg_type *reg_type,

			    struct btf **btf, u32 *btf_id, bool *is_retval)

			    struct btf **btf, u32 *btf_id, bool *is_retval, bool is_ldsx)

{

	struct bpf_insn_access_aux info = {

		.reg_type = *reg_type,

		.log = &env->log,

		.is_retval = false,

		.is_ldsx = is_ldsx,

	};









	if (env->ops->is_valid_access &&








@@ -6844,7 +6845,7 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn







			return err;

















		err = check_ctx_access(env, insn_idx, off, size, t, &reg_type, &btf,









				       &btf_id, &is_retval);









				       &btf_id, &is_retval, is_ldsx);









		if (err)









			verbose_linfo(env, insn_idx, "; ");









		if (!err && t == BPF_READ && value_regno >= 0) {
































net/core/filter.c



+16
−5






























Original line number
Diff line number
Diff line







@@ -8601,13 +8601,16 @@ static bool bpf_skb_is_valid_access(int off, int size, enum bpf_access_type type







		if (off + size > offsetofend(struct __sk_buff, cb[4]))









			return false;









		break;









	case bpf_ctx_range(struct __sk_buff, data):









	case bpf_ctx_range(struct __sk_buff, data_meta):









	case bpf_ctx_range(struct __sk_buff, data_end):









		if (info->is_ldsx || size != size_default)









			return false;









		break;









	case bpf_ctx_range_till(struct __sk_buff, remote_ip6[0], remote_ip6[3]):









	case bpf_ctx_range_till(struct __sk_buff, local_ip6[0], local_ip6[3]):









	case bpf_ctx_range_till(struct __sk_buff, remote_ip4, remote_ip4):









	case bpf_ctx_range_till(struct __sk_buff, local_ip4, local_ip4):









	case bpf_ctx_range(struct __sk_buff, data):









	case bpf_ctx_range(struct __sk_buff, data_meta):









	case bpf_ctx_range(struct __sk_buff, data_end):









		if (size != size_default)









			return false;









		break;








@@ -9051,6 +9054,14 @@ static bool xdp_is_valid_access(int off, int size,







			}









		}









		return false;









	} else {









		switch (off) {









		case offsetof(struct xdp_md, data_meta):









		case offsetof(struct xdp_md, data):









		case offsetof(struct xdp_md, data_end):









			if (info->is_ldsx)









				return false;









		}









	}



















	switch (off) {








@@ -9381,12 +9392,12 @@ static bool flow_dissector_is_valid_access(int off, int size,

















	switch (off) {









	case bpf_ctx_range(struct __sk_buff, data):









		if (size != size_default)









		if (info->is_ldsx || size != size_default)









			return false;









		info->reg_type = PTR_TO_PACKET;









		return true;









	case bpf_ctx_range(struct __sk_buff, data_end):









		if (size != size_default)









		if (info->is_ldsx || size != size_default)









			return false;









		info->reg_type = PTR_TO_PACKET_END;









		return true;