diff options
author | Jussi Maki <joamaki@gmail.com> | 2021-11-03 13:47:36 -0700 |
---|---|---|
committer | Daniel Borkmann <daniel@iogearbox.net> | 2021-11-09 01:05:34 +0100 |
commit | b2c4618162ec615a15883a804cce7e27afecfa58 (patch) | |
tree | b0c5f7731a3181f229bba8d6b93980e209bd2abc /net/core | |
parent | e0dc3b93bd7bcff8c3813d1df43e0908499c7cf0 (diff) | |
download | linux-b2c4618162ec615a15883a804cce7e27afecfa58.tar.bz2 |
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 in 84f44df664e9 ("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: 16137b09a66f2 ("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
Diffstat (limited to 'net/core')
-rw-r--r-- | net/core/filter.c | 36 |
1 files changed, 30 insertions, 6 deletions
diff --git a/net/core/filter.c b/net/core/filter.c index c3936d0724b8..e471c9b09670 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -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; } |