[PATCH bpf v5 1/2] bpf: guard sock_ops rtt_min against non-locked tcp_sock

[Werner Kasselman]

sock_ops_convert_ctx_access() reads rtt_min without the is_locked_tcp_sock guard used for every other tcp_sock field. On request_sock-backed sock_ops callbacks, sk points at a tcp_request_sock and the converted load reads past the end of the allocation.

Extract the guarded tcp_sock field load sequence into SOCK_OPS_LOAD_TCP_SOCK_FIELD() and use it for the rtt_min access after computing the sub-field offset with offsetof(struct minmax_sample, v). Reusing the shared helper keeps rtt_min aligned with the other guarded tcp_sock field loads and preserves the dst_reg == src_reg failure path that zeros the destination register when the guard fails.

Found via AST-based call-graph analysis using sqry.

Fixes: 44f0e43037d3 ("bpf: Add support for reading sk_state and more")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Werner Kasselman <werner@xxxxxxxxxxx>
---
 net/core/filter.c | 36 ++++++++++++++++++------------------
 1 file changed, 18 insertions(+), 18 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index fcfcb72663ca..2e7c33d00749 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -10535,12 +10535,10 @@ static u32 sock_ops_convert_ctx_access(enum bpf_access_type type,
 	struct bpf_insn *insn = insn_buf;
 	int off;
 
-/* Helper macro for adding read access to tcp_sock or sock fields. */
-#define SOCK_OPS_GET_FIELD(BPF_FIELD, OBJ_FIELD, OBJ)			      \
+/* Helper macro for adding guarded read access to tcp_sock fields. */
+#define SOCK_OPS_LOAD_TCP_SOCK_FIELD(FIELD_SIZE, FIELD_OFFSET)		      \
 	do {								      \
 		int fullsock_reg = si->dst_reg, reg = BPF_REG_9, jmp = 2;     \
-		BUILD_BUG_ON(sizeof_field(OBJ, OBJ_FIELD) >		      \
-			     sizeof_field(struct bpf_sock_ops, BPF_FIELD));   \
 		if (si->dst_reg == reg || si->src_reg == reg)		      \
 			reg--;						      \
 		if (si->dst_reg == reg || si->src_reg == reg)		      \
@@ -10548,7 +10546,7 @@ static u32 sock_ops_convert_ctx_access(enum bpf_access_type type,
 		if (si->dst_reg == si->src_reg) {			      \
 			*insn++ = BPF_STX_MEM(BPF_DW, si->src_reg, reg,	      \
 					  offsetof(struct bpf_sock_ops_kern,  \
-					  temp));			      \
+						   temp));		      \
 			fullsock_reg = reg;				      \
 			jmp += 2;					      \
 		}							      \
@@ -10562,24 +10560,31 @@ static u32 sock_ops_convert_ctx_access(enum bpf_access_type type,
 		if (si->dst_reg == si->src_reg)				      \
 			*insn++ = BPF_LDX_MEM(BPF_DW, reg, si->src_reg,	      \
 				      offsetof(struct bpf_sock_ops_kern,      \
-				      temp));				      \
+					       temp));			      \
 		*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(			      \
 						struct bpf_sock_ops_kern, sk),\
 				      si->dst_reg, si->src_reg,		      \
 				      offsetof(struct bpf_sock_ops_kern, sk));\
-		*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(OBJ,		      \
-						       OBJ_FIELD),	      \
+		*insn++ = BPF_LDX_MEM(FIELD_SIZE,			      \
 				      si->dst_reg, si->dst_reg,		      \
-				      offsetof(OBJ, OBJ_FIELD));	      \
+				      FIELD_OFFSET);			      \
 		if (si->dst_reg == si->src_reg)	{			      \
 			*insn++ = BPF_JMP_A(2);				      \
 			*insn++ = BPF_LDX_MEM(BPF_DW, reg, si->src_reg,	      \
 				      offsetof(struct bpf_sock_ops_kern,      \
-				      temp));				      \
+					       temp));			      \
 			*insn++ = BPF_MOV64_IMM(si->dst_reg, 0);	      \
 		}							      \
 	} while (0)
 
+#define SOCK_OPS_GET_FIELD(BPF_FIELD, OBJ_FIELD, OBJ)			      \
+	do {								      \
+		BUILD_BUG_ON(sizeof_field(OBJ, OBJ_FIELD) >		      \
+			     sizeof_field(struct bpf_sock_ops, BPF_FIELD));   \
+		SOCK_OPS_LOAD_TCP_SOCK_FIELD(BPF_FIELD_SIZEOF(OBJ, OBJ_FIELD),\
+					     offsetof(OBJ, OBJ_FIELD));       \
+	} while (0)
+
 #define SOCK_OPS_GET_SK()							      \
 	do {								      \
 		int fullsock_reg = si->dst_reg, reg = BPF_REG_9, jmp = 1;     \
@@ -10822,14 +10827,9 @@ static u32 sock_ops_convert_ctx_access(enum bpf_access_type type,
 			     sizeof(struct minmax));
 		BUILD_BUG_ON(sizeof(struct minmax) <
 			     sizeof(struct minmax_sample));
-
-		*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(
-						struct bpf_sock_ops_kern, sk),
-				      si->dst_reg, si->src_reg,
-				      offsetof(struct bpf_sock_ops_kern, sk));
-		*insn++ = BPF_LDX_MEM(BPF_W, si->dst_reg, si->dst_reg,
-				      offsetof(struct tcp_sock, rtt_min) +
-				      sizeof_field(struct minmax_sample, t));
+		off = offsetof(struct tcp_sock, rtt_min) +
+		      offsetof(struct minmax_sample, v);
+		SOCK_OPS_LOAD_TCP_SOCK_FIELD(BPF_W, off);
 		break;
 
 	case offsetof(struct bpf_sock_ops, bpf_sock_ops_cb_flags):
-- 
2.43.0