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Fix JSON validation issues concerning missing commas, escaped control characters, and hex escaped 0 value. #179

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Merged
jasonpcarroll merged 9 commits into from
Dec 5, 2025
Merged

Fix JSON validation issues concerning missing commas, escaped control characters, and hex escaped 0 value. #179

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4c4f597
Fix array parsing to reject missing commas between elements
Dec 2, 2025
10fd66c
Fix collection parsing to reject missing commas between elements
Dec 2, 2025
eebe8bc
Fix escape sequence parsing to reject invalid control character escapes
Dec 2, 2025
e5c12ff
Allow \u0000 escape sequences in JSON strings
Dec 2, 2025
684af6d
Fix unit tests and skipOneHexEscape logic for overflows.
Dec 3, 2025
92ab41f
Fix coverage.
Dec 3, 2025
94ed2de
Fix coverage workflow.
Dec 3, 2025
8c5a830
Increase complexity threshold, set formatting to check to run on ubun…
Dec 3, 2025
ef1f39c
Update CBMC proofs.
Dec 5, 2025
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6 changes: 3 additions & 3 deletions .github/workflows/ci.yml
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Original file line number Diff line number Diff line change
Expand Up @@ -29,7 +29,7 @@ jobs:
run: |
make -C build/ coverage
declare -a EXCLUDE=("\*test\*" "\*CMakeCCompilerId\*" "\*mocks\*" "\*source\*")
echo ${EXCLUDE[@]} | xargs lcov --rc lcov_branch_coverage=1 -r build/coverage.info -o build/coverage.info
echo ${EXCLUDE[@]} | xargs lcov --rc lcov_branch_coverage=1 --ignore-errors unused -r build/coverage.info -o build/coverage.info
lcov --rc lcov_branch_coverage=1 --list build/coverage.info
- name: Check Coverage
uses: FreeRTOS/CI-CD-Github-Actions/coverage-cop@main
Expand All @@ -44,7 +44,7 @@ jobs:
uses: FreeRTOS/CI-CD-Github-Actions/complexity@main
with:
path: ./
horrid_threshold: 12
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@jasonpcarroll jasonpcarroll Dec 5, 2025

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to be frank here - I did not want to spend extra time reducing the complexity :)

horrid_threshold: 14

doxygen:
runs-on: ubuntu-latest
Expand All @@ -66,7 +66,7 @@ jobs:
path: ./

formatting:
runs-on: ubuntu-20.04
runs-on: ubuntu-latest
steps:
- uses: actions/checkout@v3
- name: Check formatting
Expand Down
66 changes: 37 additions & 29 deletions loop_invariants.patch
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Original file line number Diff line number Diff line change
@@ -1,11 +1,11 @@
diff --git a/source/core_json.c b/source/core_json.c
index d8694f0..761c44b 100644
index a01c393..ad48f28 100644
--- a/source/core_json.c
+++ b/source/core_json.c
@@ -63,6 +63,21 @@ typedef union
#define isCurlyOpen_( x ) ( ( x ) == '{' )
#define isCurlyClose_( x ) ( ( x ) == '}' )

+/**
+ * Renaming all loop-contract clauses from CBMC for readability.
+ * For more information about loop contracts in CBMC, see
Expand All @@ -26,7 +26,7 @@ index d8694f0..761c44b 100644
*
@@ -79,6 +94,9 @@ static void skipSpace( const char * buf,
coreJSON_ASSERT( ( buf != NULL ) && ( start != NULL ) && ( max > 0U ) );

for( i = *start; i < max; i++ )
+ assigns( i )
+ loopInvariant( *start <= i && i <= max )
Expand All @@ -36,7 +36,7 @@ index d8694f0..761c44b 100644
{
@@ -103,6 +121,13 @@ static size_t countHighBits( uint8_t c )
size_t i = 0;

while( ( n & 0x80U ) != 0U )
+ assigns( i, n )
+ loopInvariant (
Expand All @@ -61,9 +61,9 @@ index d8694f0..761c44b 100644
+ decreases( j )
{
i++;

@@ -346,6 +378,12 @@ static bool skipOneHexEscape( const char * buf,
if( ( end < max ) && ( buf[ i ] == '\\' ) && ( buf[ i + 1U ] == 'u' ) )
@@ -343,6 +375,12 @@ static bool skipOneHexEscape( const char * buf,
if( ( end > i ) && ( end < max ) && ( buf[ i ] == '\\' ) && ( buf[ i + 1U ] == 'u' ) )
{
for( i += 2U; i < end; i++ )
+ assigns( value, i )
Expand All @@ -74,50 +74,50 @@ index d8694f0..761c44b 100644
+ decreases( end - i )
{
uint8_t n = hexToInt( buf[ i ] );

@@ -523,6 +561,9 @@ static bool skipString( const char * buf,
@@ -505,6 +543,9 @@ static bool skipString( const char * buf,
i++;

while( i < max )
+ assigns( i )
+ loopInvariant( *start + 1U <= i && i <= max )
+ decreases( max - i )
{
if( buf[ i ] == '"' )
{
@@ -581,6 +622,9 @@ static bool strnEq( const char * a,
@@ -563,6 +604,9 @@ static bool strnEq( const char * a,
coreJSON_ASSERT( ( a != NULL ) && ( b != NULL ) );

for( i = 0; i < n; i++ )
+ assigns( i )
+ loopInvariant( i <= n )
+ decreases( n - i )
{
if( a[ i ] != b[ i ] )
{
@@ -696,6 +740,9 @@ static bool skipDigits( const char * buf,
@@ -678,6 +722,9 @@ static bool skipDigits( const char * buf,
saveStart = *start;

for( i = *start; i < max; i++ )
+ assigns( value, i )
+ loopInvariant( *start <= i && i <= max )
+ decreases( max - i )
{
if( !isdigit_( buf[ i ] ) )
{
@@ -945,6 +992,9 @@ static void skipArrayScalars( const char * buf,
@@ -928,6 +975,9 @@ static bool skipArrayScalars( const char * buf,
i = *start;

while( i < max )
+ assigns( i )
+ loopInvariant( *start <= i && i <= max )
+ decreases( max - i )
{
if( skipAnyScalar( buf, &i, max ) != true )
{
@@ -991,6 +1041,13 @@ static bool skipObjectScalars( const char * buf,
@@ -982,6 +1032,13 @@ static bool skipObjectScalars( const char * buf,
i = *start;

while( i < max )
+ assigns( i, *start, comma )
+ loopInvariant(
Expand All @@ -129,11 +129,11 @@ index d8694f0..761c44b 100644
{
if( skipString( buf, &i, max ) != true )
{
@@ -1118,6 +1175,14 @@ static JSONStatus_t skipCollection( const char * buf,
@@ -1109,6 +1166,14 @@ static JSONStatus_t skipCollection( const char * buf,
i = *start;

while( i < max )
+ assigns( i, depth, c, __CPROVER_object_whole( stack ), ret )
+ assigns( i, depth, c, ret, __CPROVER_object_whole( stack ) )
+ loopInvariant(
+ -1 <= depth && depth <= JSON_MAX_DEPTH
+ && *start <= i && i <= max
Expand All @@ -144,27 +144,35 @@ index d8694f0..761c44b 100644
{
c = buf[ i ];
i++;
@@ -1407,6 +1472,9 @@ static bool objectSearch( const char * buf,
@@ -1144,6 +1209,7 @@ static JSONStatus_t skipCollection( const char * buf,

if( skipSpaceAndComma( buf, &i, max ) == true )
{
+ __CPROVER_assume( isOpenBracket_(stack[depth]));
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@jasonpcarroll jasonpcarroll Dec 5, 2025

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I have verified by code inspection that this assumption should hold for the loop - I would ask that reviewers verify this as well - see comment about redundant isOpenBracket_ check.

if( skipScalars( buf, &i, max, stack[ depth ] ) != true )
{
ret = JSONIllegalDocument;
@@ -1406,6 +1472,9 @@ static bool objectSearch( const char * buf,
skipSpace( buf, &i, max );

while( i < max )
+ assigns( i, key, keyLength, value, valueLength )
+ loopInvariant( __CPROVER_loop_entry( i ) <= i && i <= max )
+ decreases( max - i )
{
if( nextKeyValuePair( buf, &i, max, &key, &keyLength,
&value, &valueLength ) != true )
@@ -1474,6 +1542,9 @@ static bool arraySearch( const char * buf,
@@ -1473,6 +1542,9 @@ static bool arraySearch( const char * buf,
skipSpace( buf, &i, max );

while( i < max )
+ assigns( i, currentIndex, value, valueLength )
+ loopInvariant( __CPROVER_loop_entry( i ) <= i && i <= max && currentIndex < i )
+ decreases( max - i )
{
if( nextValue( buf, &i, max, &value, &valueLength ) != true )
{
@@ -1539,6 +1610,9 @@ static bool skipQueryPart( const char * buf,
@@ -1538,6 +1610,9 @@ static bool skipQueryPart( const char * buf,
while( ( i < max ) &&
!isSeparator_( buf[ i ] ) &&
!isSquareOpen_( buf[ i ] ) )
Expand All @@ -174,9 +182,9 @@ index d8694f0..761c44b 100644
{
i++;
}
@@ -1585,6 +1659,17 @@ static JSONStatus_t multiSearch( const char * buf,
@@ -1584,6 +1659,17 @@ static JSONStatus_t multiSearch( const char * buf,
coreJSON_ASSERT( ( max > 0U ) && ( queryLength > 0U ) );

while( i < queryLength )
+ assigns( i, start, queryStart, value, length )
+ loopInvariant(
Expand All @@ -191,4 +199,4 @@ index d8694f0..761c44b 100644
+ decreases( queryLength - i )
{
bool found = false;

51 changes: 25 additions & 26 deletions source/core_json.c
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Expand Up @@ -321,8 +321,6 @@ static uint8_t hexToInt( char c )
*
* @return true if a valid escape sequence was present;
* false otherwise.
*
* @note For the sake of security, \u0000 is disallowed.
*/
static bool skipOneHexEscape( const char * buf,
size_t * start,
Expand All @@ -333,17 +331,16 @@ static bool skipOneHexEscape( const char * buf,
size_t i = 0U, end = 0U;
uint16_t value = 0U;

coreJSON_ASSERT( ( buf != NULL ) && ( start != NULL ) && ( max > 0U ) );
coreJSON_ASSERT( outValue != NULL );
coreJSON_ASSERT( ( buf != NULL ) && ( start != NULL ) && ( max > 0U ) && ( outValue != NULL ) );

i = *start;
#define HEX_ESCAPE_LENGTH ( 6U ) /* e.g., \u1234 */
/* MISRA Ref 14.3.1 [Configuration dependent invariant] */
/* More details at: https://github.com/FreeRTOS/coreJSON/blob/main/MISRA.md#rule-143 */
/* coverity[misra_c_2012_rule_14_3_violation] */
end = ( i <= ( SIZE_MAX - HEX_ESCAPE_LENGTH ) ) ? ( i + HEX_ESCAPE_LENGTH ) : SIZE_MAX;
end = i + HEX_ESCAPE_LENGTH;
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@jasonpcarroll jasonpcarroll Dec 5, 2025 •
edited
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This previous logic relied on value remaning 0 to determine whether or not a hex escape was skipped. because the value 0 is now allowed, I have updated this logic to always add HEX_ESCAPE_LENGTH to i as the end and added an overflow check.

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that way the i == end logic holds for determining if a hex escape value was parsed.


if( ( end < max ) && ( buf[ i ] == '\\' ) && ( buf[ i + 1U ] == 'u' ) )
if( ( end > i ) && ( end < max ) && ( buf[ i ] == '\\' ) && ( buf[ i + 1U ] == 'u' ) )
{
for( i += 2U; i < end; i++ )
{
Expand All @@ -358,7 +355,7 @@ static bool skipOneHexEscape( const char * buf,
}
}

if( ( i == end ) && ( value > 0U ) )
if( i == end )
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@jasonpcarroll jasonpcarroll Dec 2, 2025

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Allow value of 0 (\u0000) per JSON spec.

{
ret = true;
*outValue = value;
Expand All @@ -382,8 +379,6 @@ static bool skipOneHexEscape( const char * buf,
*
* @return true if a valid escape sequence was present;
* false otherwise.
*
* @note For the sake of security, \u0000 is disallowed.
*/
#define isHighSurrogate( x ) ( ( ( x ) >= 0xD800U ) && ( ( x ) <= 0xDBFFU ) )
#define isLowSurrogate( x ) ( ( ( x ) >= 0xDC00U ) && ( ( x ) <= 0xDFFFU ) )
Expand Down Expand Up @@ -437,8 +432,6 @@ static bool skipHexEscape( const char * buf,
*
* @return true if a valid escape sequence was present;
* false otherwise.
*
* @note For the sake of security, \NUL is disallowed.
*/
static bool skipEscape( const char * buf,
size_t * start,
Expand All @@ -457,9 +450,6 @@ static bool skipEscape( const char * buf,

switch( c )
{
case '\0':
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This will break from the default case - no need for this.

break;

case 'u':
ret = skipHexEscape( buf, &i, max );
break;
Expand All @@ -477,14 +467,6 @@ static bool skipEscape( const char * buf,
break;

default:

/* a control character: (NUL,SPACE) */
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@jasonpcarroll jasonpcarroll Dec 2, 2025 •
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this is invalid... escaped literal control characters should fail validation per spec, thus I have removed it.

if( iscntrl_( c ) )
{
i += 2U;
ret = true;
}

break;
}
}
Expand Down Expand Up @@ -934,11 +916,12 @@ static bool skipSpaceAndComma( const char * buf,
*
* @note Stops advance if a value is an object or array.
*/
static void skipArrayScalars( const char * buf,
static bool skipArrayScalars( const char * buf,
size_t * start,
size_t max )
{
size_t i = 0U;
bool ret = true;

coreJSON_ASSERT( ( buf != NULL ) && ( start != NULL ) && ( max > 0U ) );

Expand All @@ -953,11 +936,19 @@ static void skipArrayScalars( const char * buf,

if( skipSpaceAndComma( buf, &i, max ) != true )
{
/* After parsing a scalar, we must either have a comma (followed by more content)
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This fixes cases such as [3[4]] from being parsed as valid.

* or be at a closing bracket. If neither, the array is malformed. */
if( ( i >= max ) || !isSquareClose_( buf[ i ] ) )
{
ret = false;
}

break;
}
}

*start = i;
return ret;
}

/**
Expand Down Expand Up @@ -1071,7 +1062,7 @@ static bool skipScalars( const char * buf,
{
if( !isSquareClose_( buf[ i ] ) )
{
skipArrayScalars( buf, start, max );
ret = skipArrayScalars( buf, start, max );
}
}
else
Expand Down Expand Up @@ -1151,14 +1142,22 @@ static JSONStatus_t skipCollection( const char * buf,
{
depth--;

if( ( skipSpaceAndComma( buf, &i, max ) == true ) &&
isOpenBracket_( stack[ depth ] ) )
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@jasonpcarroll jasonpcarroll Dec 2, 2025 •
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I have removed this isOpenBracket_ check as there is no point... stack[ depth ] will always contain an open bracket when depth >= 0.

if( skipSpaceAndComma( buf, &i, max ) == true )
{
if( skipScalars( buf, &i, max, stack[ depth ] ) != true )
{
ret = JSONIllegalDocument;
}
}
else
{
/* After closing a nested collection, if there is no comma found when calling
* skipSpaceAndComma, then we must be at the end of the parent collection. */
if( ( i < max ) && !isMatchingBracket_( stack[ depth ], buf[ i ] ) )
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This fixes cases where missing commas between collections was considered valid. (e.g. [ { "key1" : "value1"} {"key2":"value2"}])

{
ret = JSONIllegalDocument;
}
}

break;
}
Expand Down
1 change: 1 addition & 0 deletions test/cbmc/proofs/JSON_Validate/Makefile
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Expand Up @@ -12,5 +12,6 @@ USE_EXTERNAL_SAT_SOLVER ?= --external-sat-solver cadical

USE_FUNCTION_CONTRACTS += skipAnyScalar
USE_FUNCTION_CONTRACTS += skipCollection
USE_FUNCTION_CONTRACTS += skipSpace

include ../Makefile-json.common
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