inet_diag: validate port comparison byte code to prevent unsafe reads

Add logic to verify that a port comparison byte code operation
actually has the second inet_diag_bc_op from which we read the port
for such operations.

Previously the code blindly referenced op[1] without first checking
whether a second inet_diag_bc_op struct could fit there. So a
malicious user could make the kernel read 4 bytes beyond the end of
the bytecode array by claiming to have a whole port comparison byte
code (2 inet_diag_bc_op structs) when in fact the bytecode was not
long enough to hold both.

Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 24 insertions, 7 deletions

diff --git a/net/ipv4/inet_diag.c b/net/ipv4/inet_diag.c
index 95f1a458371d..e23e16dc501d 100644
--- a/net/ipv4/inet_diag.c
+++ b/net/ipv4/inet_diag.c
@@ -557,6 +557,17 @@ static bool valid_hostcond(const struct inet_diag_bc_op *op, int len,
         return true;
 }
 
+/* Validate a port comparison operator. */
+static inline bool valid_port_comparison(const struct inet_diag_bc_op *op,
+                                         int len, int *min_len)
+{
+        /* Port comparisons put the port in a follow-on inet_diag_bc_op. */
+        *min_len += sizeof(struct inet_diag_bc_op);
+        if (len < *min_len)
+                return false;
+        return true;
+}
+
 static int inet_diag_bc_audit(const void *bytecode, int bytecode_len)
 {
         const void *bc = bytecode;
@@ -572,24 +583,30 @@ static int inet_diag_bc_audit(const void *bytecode, int bytecode_len)
                 case INET_DIAG_BC_D_COND:
                         if (!valid_hostcond(bc, len, &min_len))
                                 return -EINVAL;
-                        /* fall through */
-                case INET_DIAG_BC_AUTO:
+                        break;
                 case INET_DIAG_BC_S_GE:
                 case INET_DIAG_BC_S_LE:
                 case INET_DIAG_BC_D_GE:
                 case INET_DIAG_BC_D_LE:
-                case INET_DIAG_BC_JMP:
-                        if (op->no < min_len || op->no > len + 4 || op->no & 3)
-                                return -EINVAL;
-                        if (op->no < len &&
-                            !valid_cc(bytecode, bytecode_len, len - op->no))
+                        if (!valid_port_comparison(bc, len, &min_len))
                                 return -EINVAL;
                         break;
+                case INET_DIAG_BC_AUTO:
+                case INET_DIAG_BC_JMP:
                 case INET_DIAG_BC_NOP:
                         break;
                 default:
                         return -EINVAL;
                 }
+
+                if (op->code != INET_DIAG_BC_NOP) {
+                        if (op->no < min_len || op->no > len + 4 || op->no & 3)
+                                return -EINVAL;
+                        if (op->no < len &&
+                            !valid_cc(bytecode, bytecode_len, len - op->no))
+                                return -EINVAL;
+                }
+
                 if (op->yes < min_len || op->yes > len + 4 || op->yes & 3)
                         return -EINVAL;
                 bc  += op->yes;