[PATCH net] inet_diag: validate port comparison byte code to prevent unsafe reads

[PATCH net] inet_diag: validate port comparison byte code to prevent unsafe reads

[Neal Cardwell]

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>
---
[Patch was generated relative to the previous 3-patch inet_diag patch series
 from last night.]
 net/ipv4/inet_diag.c |   30 +++++++++++++++++++++++-------
 1 files changed, 23 insertions(+), 7 deletions(-)

diff --git a/net/ipv4/inet_diag.c b/net/ipv4/inet_diag.c
index 95f1a45..67746f5 100644
--- a/net/ipv4/inet_diag.c
+++ b/net/ipv4/inet_diag.c
@@ -557,6 +557,16 @@ 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;
+}
+
 static int inet_diag_bc_audit(const void *bytecode, int bytecode_len)
 {
 	const void *bc = bytecode;
@@ -572,24 +582,30 @@ 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;
-- 
1.7.7.3

[PATCH net] inet_diag: validate port comparison byte code to prevent unsafe reads

[Neal Cardwell]

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>
---
[Patch was generated relative to the previous 3-patch inet_diag patch series
 from last night.]
 net/ipv4/inet_diag.c |   30 +++++++++++++++++++++++-------
 1 files changed, 23 insertions(+), 7 deletions(-)

diff --git a/net/ipv4/inet_diag.c b/net/ipv4/inet_diag.c
index 95f1a45..67746f5 100644
--- a/net/ipv4/inet_diag.c
+++ b/net/ipv4/inet_diag.c
@@ -557,6 +557,16 @@ 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;
+}
+
 static int inet_diag_bc_audit(const void *bytecode, int bytecode_len)
 {
 	const void *bc = bytecode;
@@ -572,24 +582,30 @@ 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;
-- 
1.7.7.3

Re: [PATCH net] inet_diag: validate port comparison byte code to prevent unsafe reads

[David Miller]

From: Neal Cardwell <ncardwell@google.com>
Date: Sun,  9 Dec 2012 16:03:00 -0500

> 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>

Haste makes waste...

> +/* 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;
> +}
> +

I added the missing "return true" at the end of this new function.

Applied, but please be more careful and at least look at the compiler
warnings when you submit your changes.

Thanks.

Re: [PATCH net] inet_diag: validate port comparison byte code to prevent unsafe reads

[Neal Cardwell]

On Sun, Dec 9, 2012 at 7:02 PM, David Miller <davem@davemloft.net> wrote:
> I added the missing "return true" at the end of this new function.
>
> Applied, but please be more careful and at least look at the compiler
> warnings when you submit your changes.
>
> Thanks.

Roger that. Oof. Can't believe I missed that.

thanks,
neal