CVE-2017-18367 (published 2019-04-24T21:29Z)

libseccomp-golang 0.9.0 and earlier incorrectly generates BPFs that OR multiple arguments rather than ANDing them. A process running under a restrictive seccomp filter that specified multiple syscall arguments could bypass intended access restrictions by specifying a single matching argument.

Severity: MEDIUM
CVSS v2 base score: 5.0 (AV:N/AC:L/Au:N/C:N/I:P/A:N)
CVSS v3 base score: 7.5, HIGH (CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N)

Weakness information:
cwe_id: CWE-20
cwe_name: Improper Input Validation
description: The product receives input or data, but it does
        not validate or incorrectly validates that the input has the
        properties that are required to process the data safely and
        correctly.
extended_description: 
	   Input validation is a frequently-used technique
	   for checking potentially dangerous inputs in order to
	   ensure that the inputs are safe for processing within the
	   code, or when communicating with other components.  When
	   software does not validate input properly, an attacker is
	   able to craft the input in a form that is not expected by
	   the rest of the application. This will lead to parts of the
	   system receiving unintended input, which may result in
	   altered control flow, arbitrary control of a resource, or
	   arbitrary code execution.
	   Input validation is not the only technique for
	   processing input, however.  Other techniques attempt to
	   transform potentially-dangerous input into something safe, such
	   as filtering (CWE-790) - which attempts to remove dangerous
	   inputs - or encoding/escaping (CWE-116), which attempts to
	   ensure that the input is not misinterpreted when it is included
	   in output to another component. Other techniques exist as well
	   (see CWE-138 for more examples.)
	   Input validation can be applied to:
	   
	     raw data - strings, numbers, parameters, file contents, etc.
	     metadata - information about the raw data, such as headers or size
	   
	   Data can be simple or structured.  Structured data
	   can be composed of many nested layers, composed of
	   combinations of metadata and raw data, with other simple or
	   structured data.
	   Many properties of raw data or metadata may need
	   to be validated upon entry into the code, such
	   as:
	   
	     specified quantities such as size, length, frequency, price, rate, number of operations, time, etc.
	     implied or derived quantities, such as the actual size of a file instead of a specified size
	     indexes, offsets, or positions into more complex data structures
	     symbolic keys or other elements into hash tables, associative arrays, etc.
	     well-formedness, i.e. syntactic correctness - compliance with expected syntax 
	     lexical token correctness - compliance with rules for what is treated as a token
	     specified or derived type - the actual type of the input (or what the input appears to be)
	     consistency - between individual data elements, between raw data and metadata, between references, etc.
	     conformance to domain-specific rules, e.g. business logic 
	     equivalence - ensuring that equivalent inputs are treated the same
	     authenticity, ownership, or other attestations about the input, e.g. a cryptographic signature to prove the source of the data
	   
	   Implied or derived properties of data must often
	   be calculated or inferred by the code itself.  Errors in
	   deriving properties may be considered a contributing factor
	   to improper input validation.
	   
	   Note that "input validation" has very different
	   meanings to different people, or within different
	   classification schemes.  Caution must be used when
	   referencing this CWE entry or mapping to it.  For example,
	   some weaknesses might involve inadvertently giving control
	   to an attacker over an input when they should not be able
	   to provide an input at all, but sometimes this is referred
	   to as input validation.
	   Finally, it is important to emphasize that the
	   distinctions between input validation and output escaping
	   are often blurred, and developers must be careful to
	   understand the difference, including how input validation
	   is not always sufficient to prevent vulnerabilities,
	   especially when less stringent data types must be
	   supported, such as free-form text. Consider a SQL injection
	   scenario in which a person's last name is inserted into a
	   query. The name "O'Reilly" would likely pass the validation
	   step since it is a common last name in the English
	   language. However, this valid name cannot be directly
	   inserted into the database because it contains the "'"
	   apostrophe character, which would need to be escaped or
	   otherwise transformed. In this case, removing the
	   apostrophe might reduce the risk of SQL injection, but it
	   would produce incorrect behavior because the wrong name
	   would be recorded.
       
         

Fix information:
repo_url: https://github.com/seccomp/libseccomp-golang
commit_details: repo_url: https://github.com/seccomp/libseccomp-golang
author: Matthew Heon
author_date: 2017-04-19 16:28:29-04:00
msg: golang: Resolve bug with handling of multiple argument rules

In the upstream library, when added with a single API call,
multiple syscall argument rules should be matched with AND
logic - if all of them match, the rule matches.

At present, the Golang bindings apply OR logic to this case.
This commit resolves this and reverts to the behavior of the
main library.

Signed-off-by: Matthew Heon <matthew.heon@gmail.com>
repository: repo_url: https://github.com/seccomp/libseccomp-golang
repo_name: seccomp/libseccomp-golang
description: The libseccomp golang bindings repository
repo_language: Go
owner: seccomp
file_changes: filename: seccomp_internal.go
change_type: ModificationType.MODIFY
diff: @@ -120,23 +120,27 @@ unsigned int get_micro_version()
 
 typedef struct scmp_arg_cmp* scmp_cast_t;
 
-// Wrapper to create an scmp_arg_cmp struct
-void*
-make_struct_arg_cmp(
-                    unsigned int arg,
-                    int compare,
-                    uint64_t a,
-                    uint64_t b
-                   )
+void* make_arg_cmp_array(unsigned int length)
 {
-	struct scmp_arg_cmp *s = malloc(sizeof(struct scmp_arg_cmp));
+        return calloc(length, sizeof(struct scmp_arg_cmp));
+}
 
-	s->arg = arg;
-	s->op = compare;
-	s->datum_a = a;
-	s->datum_b = b;
+// Wrapper to add an scmp_arg_cmp struct to an existing arg_cmp array
+void add_struct_arg_cmp(
+                        struct scmp_arg_cmp* arr,
+                        unsigned int pos,
+                        unsigned int arg,
+                        int compare,
+                        uint64_t a,
+                        uint64_t b
+                       )
+{
+        arr[pos].arg = arg;
+        arr[pos].op = compare;
+        arr[pos].datum_a = a;
+        arr[pos].datum_b = b;
 
-	return s;
+        return;
 }
 */
 import "C"
@@ -239,12 +243,9 @@ func (f *ScmpFilter) setFilterAttr(attr scmpFilterAttr, value C.uint32_t) error
 // DOES NOT LOCK OR CHECK VALIDITY
 // Assumes caller has already done this
 // Wrapper for seccomp_rule_add_... functions
-func (f *ScmpFilter) addRuleWrapper(call ScmpSyscall, action ScmpAction, exact bool, cond C.scmp_cast_t) error {
-	var length C.uint
-	if cond != nil {
-		length = 1
-	} else {
-		length = 0
+func (f *ScmpFilter) addRuleWrapper(call ScmpSyscall, action ScmpAction, exact bool, length C.uint, cond C.scmp_cast_t) error {
+	if length != 0 && cond == nil {
+		return fmt.Errorf("null conditions list, but length is nonzero")
 	}
 
 	var retCode C.int
@@ -258,6 +259,8 @@ func (f *ScmpFilter) addRuleWrapper(call ScmpSyscall, action ScmpAction, exact b
 		return fmt.Errorf("unrecognized syscall")
 	} else if syscall.Errno(-1*retCode) == syscall.EPERM {
 		return fmt.Errorf("requested action matches default action of filter")
+	} else if syscall.Errno(-1*retCode) == syscall.EINVAL {
+		return fmt.Errorf("two checks on same syscall argument")
 	} else if retCode != 0 {
 		return syscall.Errno(-1 * retCode)
 	}
@@ -275,7 +278,7 @@ func (f *ScmpFilter) addRuleGeneric(call ScmpSyscall, action ScmpAction, exact b
 	}
 
 	if len(conds) == 0 {
-		if err := f.addRuleWrapper(call, action, exact, nil); err != nil {
+		if err := f.addRuleWrapper(call, action, exact, 0, nil); err != nil {
 			return err
 		}
 	} else {
@@ -287,13 +290,20 @@ func (f *ScmpFilter) addRuleGeneric(call ScmpSyscall, action ScmpAction, exact b
 			}
 		}
 
-		for _, cond := range conds {
-			cmpStruct := C.make_struct_arg_cmp(C.uint(cond.Argument), cond.Op.toNative(), C.uint64_t(cond.Operand1), C.uint64_t(cond.Operand2))
-			defer C.free(cmpStruct)
+		argsArr := C.make_arg_cmp_array(C.uint(len(conds)))
+		if argsArr == nil {
+			return fmt.Errorf("error allocating memory for conditions")
+		}
+		defer C.free(argsArr)
+
+		for i, cond := range conds {
+			C.add_struct_arg_cmp(C.scmp_cast_t(argsArr), C.uint(i),
+				C.uint(cond.Argument), cond.Op.toNative(),
+				C.uint64_t(cond.Operand1), C.uint64_t(cond.Operand2))
+		}
 
-			if err := f.addRuleWrapper(call, action, exact, C.scmp_cast_t(cmpStruct)); err != nil {
-				return err
-			}
+		if err := f.addRuleWrapper(call, action, exact, C.uint(len(conds)), C.scmp_cast_t(argsArr)); err != nil {
+			return err
 		}
 	}
 

programming_language: Go