mirror of
https://github.com/torvalds/linux
synced 2024-09-06 18:01:05 +00:00
bpf, sockmap: sk_skb data_end access incorrect when src_reg = dst_reg
The current conversion of skb->data_end reads like this: ; data_end = (void*)(long)skb->data_end; 559: (79) r1 = *(u64 *)(r2 +200) ; r1 = skb->data 560: (61) r11 = *(u32 *)(r2 +112) ; r11 = skb->len 561: (0f) r1 += r11 562: (61) r11 = *(u32 *)(r2 +116) 563: (1f) r1 -= r11 But similar to the case in84f44df664
("bpf: sock_ops sk access may stomp registers when dst_reg = src_reg"), the code will read an incorrect skb->len when src == dst. In this case we end up generating this xlated code: ; data_end = (void*)(long)skb->data_end; 559: (79) r1 = *(u64 *)(r1 +200) ; r1 = skb->data 560: (61) r11 = *(u32 *)(r1 +112) ; r11 = (skb->data)->len 561: (0f) r1 += r11 562: (61) r11 = *(u32 *)(r1 +116) 563: (1f) r1 -= r11 ... where line 560 is the reading 4B of (skb->data + 112) instead of the intended skb->len Here the skb pointer in r1 gets set to skb->data and the later deref for skb->len ends up following skb->data instead of skb. This fixes the issue similarly to the patch mentioned above by creating an additional temporary variable and using to store the register when dst_reg = src_reg. We name the variable bpf_temp_reg and place it in the cb context for sk_skb. Then we restore from the temp to ensure nothing is lost. Fixes:16137b09a6
("bpf: Compute data_end dynamically with JIT code") Signed-off-by: Jussi Maki <joamaki@gmail.com> Signed-off-by: John Fastabend <john.fastabend@gmail.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com> Link: https://lore.kernel.org/bpf/20211103204736.248403-6-john.fastabend@gmail.com
This commit is contained in:
parent
e0dc3b93bd
commit
b2c4618162
|
@ -66,6 +66,10 @@ struct sk_skb_cb {
|
|||
#define SK_SKB_CB_PRIV_LEN 20
|
||||
unsigned char data[SK_SKB_CB_PRIV_LEN];
|
||||
struct _strp_msg strp;
|
||||
/* temp_reg is a temporary register used for bpf_convert_data_end_access
|
||||
* when dst_reg == src_reg.
|
||||
*/
|
||||
u64 temp_reg;
|
||||
};
|
||||
|
||||
static inline struct strp_msg *strp_msg(struct sk_buff *skb)
|
||||
|
|
|
@ -9756,22 +9756,46 @@ static u32 sock_ops_convert_ctx_access(enum bpf_access_type type,
|
|||
static struct bpf_insn *bpf_convert_data_end_access(const struct bpf_insn *si,
|
||||
struct bpf_insn *insn)
|
||||
{
|
||||
/* si->dst_reg = skb->data */
|
||||
int reg;
|
||||
int temp_reg_off = offsetof(struct sk_buff, cb) +
|
||||
offsetof(struct sk_skb_cb, temp_reg);
|
||||
|
||||
if (si->src_reg == si->dst_reg) {
|
||||
/* We need an extra register, choose and save a register. */
|
||||
reg = BPF_REG_9;
|
||||
if (si->src_reg == reg || si->dst_reg == reg)
|
||||
reg--;
|
||||
if (si->src_reg == reg || si->dst_reg == reg)
|
||||
reg--;
|
||||
*insn++ = BPF_STX_MEM(BPF_DW, si->src_reg, reg, temp_reg_off);
|
||||
} else {
|
||||
reg = si->dst_reg;
|
||||
}
|
||||
|
||||
/* reg = skb->data */
|
||||
*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct sk_buff, data),
|
||||
si->dst_reg, si->src_reg,
|
||||
reg, si->src_reg,
|
||||
offsetof(struct sk_buff, data));
|
||||
/* AX = skb->len */
|
||||
*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct sk_buff, len),
|
||||
BPF_REG_AX, si->src_reg,
|
||||
offsetof(struct sk_buff, len));
|
||||
/* si->dst_reg = skb->data + skb->len */
|
||||
*insn++ = BPF_ALU64_REG(BPF_ADD, si->dst_reg, BPF_REG_AX);
|
||||
/* reg = skb->data + skb->len */
|
||||
*insn++ = BPF_ALU64_REG(BPF_ADD, reg, BPF_REG_AX);
|
||||
/* AX = skb->data_len */
|
||||
*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct sk_buff, data_len),
|
||||
BPF_REG_AX, si->src_reg,
|
||||
offsetof(struct sk_buff, data_len));
|
||||
/* si->dst_reg = skb->data + skb->len - skb->data_len */
|
||||
*insn++ = BPF_ALU64_REG(BPF_SUB, si->dst_reg, BPF_REG_AX);
|
||||
|
||||
/* reg = skb->data + skb->len - skb->data_len */
|
||||
*insn++ = BPF_ALU64_REG(BPF_SUB, reg, BPF_REG_AX);
|
||||
|
||||
if (si->src_reg == si->dst_reg) {
|
||||
/* Restore the saved register */
|
||||
*insn++ = BPF_MOV64_REG(BPF_REG_AX, si->src_reg);
|
||||
*insn++ = BPF_MOV64_REG(si->dst_reg, reg);
|
||||
*insn++ = BPF_LDX_MEM(BPF_DW, reg, BPF_REG_AX, temp_reg_off);
|
||||
}
|
||||
|
||||
return insn;
|
||||
}
|
||||
|
|
Loading…
Reference in a new issue