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fix(SEC-3): make global symbol/lookup tables thread-safe #228

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a2e0f82
fix(SEC-3): make global symbol/lookup tables thread-safe
kostub Jun 12, 2026
d86d1bf
fix: hold gSymbolTableLock across full inner read in +latexSymbolName…
kostub Jun 12, 2026
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128 changes: 82 additions & 46 deletions iosMath/lib/MTMathAtomFactory.m
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,12 @@

#import "MTMathAtomFactory.h"
#import "MTMathListBuilder.h"
#import <os/lock.h>

// Lock protecting the two genuinely-mutable symbol tables: `commands` (in
// +supportedLatexSymbols) and `textToCommands` (in +textToLatexSymbolNames).
// Read-only tables are guarded only by dispatch_once and need no run-time lock.
static os_unfair_lock gSymbolTableLock = OS_UNFAIR_LOCK_INIT;

NSString *const MTSymbolMultiplication = @"\u00D7";
NSString *const MTSymbolDivision = @"\u00F7";
Expand Down Expand Up @@ -163,9 +169,13 @@ + (nullable MTMathAtom *)atomForLatexSymbolName:(NSString *)symbolName
// Switch to the canonical name
symbolName = canonicalName;
}

NSDictionary* commands = [self supportedLatexSymbols];
MTMathAtom* atom = commands[symbolName];

// commands is a genuinely-mutable dict (addLatexSymbol: writes it), so guard.
NSMutableDictionary* commands = [self supportedLatexSymbols];
MTMathAtom* atom = nil;
os_unfair_lock_lock(&gSymbolTableLock);
atom = commands[symbolName];
os_unfair_lock_unlock(&gSymbolTableLock);
if (atom) {
// Return a copy of the atom since atoms are mutable.
return [atom copy];
Expand All @@ -178,32 +188,43 @@ + (nullable NSString*) latexSymbolNameForAtom:(MTMathAtom*) atom
if (atom.nucleus.length == 0) {
return nil;
}
NSDictionary<NSString*, NSDictionary<NSNumber*, NSString*>*>* dict = [MTMathAtomFactory textToLatexSymbolNames];
// textToLatexSymbolNames is a genuinely-mutable dict (addLatexSymbol: writes it), and the
// per-nucleus `inner` dict is mutated in place by addLatexSymbol:, so the lock must cover the
// FULL read — both the outer dict[...] lookup and the inner[...] lookups (incl. the Bin
// fallback). Resolve `name` to a local under the lock, then copy it out before unlocking.
NSMutableDictionary* dict = [MTMathAtomFactory textToLatexSymbolNames];
NSString* name = nil;
os_unfair_lock_lock(&gSymbolTableLock);
NSDictionary<NSNumber*, NSString*>* inner = dict[atom.nucleus];
if (!inner) {
return nil;
}
NSString* name = inner[@(atom.type)];
if (name) {
return name;
}
// -[MTMathList finalized] reclassifies leading/orphan/trailing Bin atoms to Un. The
// forward table only ever registers atoms as Bin, so a (nucleus, Un)
// lookup must fall back to the Bin cell to recover the canonical name.
if (atom.type == kMTMathAtomUnaryOperator) {
return inner[@(kMTMathAtomBinaryOperator)];
if (inner) {
name = inner[@(atom.type)];
// -[MTMathList finalized] reclassifies leading/orphan/trailing Bin atoms to Un. The
// forward table only ever registers atoms as Bin, so a (nucleus, Un)
// lookup must fall back to the Bin cell to recover the canonical name.
if (!name && atom.type == kMTMathAtomUnaryOperator) {
name = inner[@(kMTMathAtomBinaryOperator)];
}
}
return nil;
// `name` is an immutable NSString stored in the dict; copy guarantees we don't hold a
// reference into the mutable container after unlocking.
NSString* result = [name copy];
os_unfair_lock_unlock(&gSymbolTableLock);
return result;
}

+ (void)addLatexSymbol:(NSString *)name value:(MTMathAtom *)atom
{
NSParameterAssert(name);
NSParameterAssert(atom);
// Ensure both tables are initialized before taking the lock (dispatch_once
// inside each accessor guarantees a single init; no deadlock since the tokens
// are method-local and the lock is not held during the once-block).
NSMutableDictionary<NSString*, MTMathAtom*>* commands = [self supportedLatexSymbols];
commands[name] = atom;
NSMutableDictionary<NSString*, NSMutableDictionary<NSNumber*, NSString*>*>* dict = [self textToLatexSymbolNames];

os_unfair_lock_lock(&gSymbolTableLock);
commands[name] = [atom copy]; // copy on write — symmetric with the read side
Comment on lines 217 to +226

@gemini-code-assist gemini-code-assist Bot Jun 12, 2026

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high

In Objective-C, assertions like NSParameterAssert are disabled in release builds. If name or atom is nil at runtime in a release build, attempting to set a value in commands or copying atom will cause an NSInvalidArgumentException crash. Always guard against nil keys and values before modifying an NSMutableDictionary.

    if (!name || !atom) {
        return;
    }
    NSMutableDictionary<NSString*, MTMathAtom*>* commands = [self supportedLatexSymbols];
    NSMutableDictionary<NSString*, NSMutableDictionary<NSNumber*, NSString*>*>* dict = [self textToLatexSymbolNames];

    os_unfair_lock_lock(&gSymbolTableLock);
    commands[name] = [atom copy];
References
  1. Always guard against nil keys before accessing or modifying an NSMutableDictionary (or NSDictionary) in Objective-C to prevent NSInvalidArgumentException crashes.

if (atom.nucleus.length != 0) {
NSMutableDictionary<NSString*, NSMutableDictionary<NSNumber*, NSString*>*>* dict = [self textToLatexSymbolNames];
NSMutableDictionary<NSNumber*, NSString*>* inner = dict[atom.nucleus];
if (!inner) {
inner = [NSMutableDictionary dictionaryWithCapacity:1];
Expand All @@ -216,12 +237,16 @@ + (void)addLatexSymbol:(NSString *)name value:(MTMathAtom *)atom
inner[typeKey] = name;
}
}
os_unfair_lock_unlock(&gSymbolTableLock);
}

+ (NSArray<NSString *> *)supportedLatexSymbolNames
{
NSDictionary<NSString*, MTMathAtom*>* commands = [MTMathAtomFactory supportedLatexSymbols];
return commands.allKeys;
NSMutableDictionary<NSString*, MTMathAtom*>* commands = [MTMathAtomFactory supportedLatexSymbols];
os_unfair_lock_lock(&gSymbolTableLock);
NSArray* keys = commands.allKeys;
os_unfair_lock_unlock(&gSymbolTableLock);
return keys;
}

+ (nullable MTAccent*) accentWithName:(NSString*) accentName
Expand Down Expand Up @@ -272,7 +297,8 @@ + (MTFontStyle)fontStyleWithName:(NSString *)fontName {
+ (NSDictionary<NSString*, NSNumber*>*) textStyles
{
static NSDictionary<NSString*, NSNumber*>* textStyles = nil;
if (!textStyles) {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
textStyles = @{
@"text": @(kMTTextStyleRoman),
@"textrm": @(kMTTextStyleRoman),
Expand All @@ -281,7 +307,7 @@ + (MTFontStyle)fontStyleWithName:(NSString *)fontName {
@"textsf": @(kMTTextStyleSansSerif),
@"texttt": @(kMTTextStyleTypewriter),
};
}
});
return textStyles;
}

Expand Down Expand Up @@ -367,14 +393,15 @@ + (nullable MTMathAtom *)tableWithEnvironment:(NSString *)env rows:(NSArray<NSAr
}
}
static NSDictionary<NSString*, NSArray*>* matrixEnvs = nil;
if (!matrixEnvs) {
static dispatch_once_t matrixEnvsOnce;
dispatch_once(&matrixEnvsOnce, ^{
matrixEnvs = @{ @"matrix" : @[],
@"pmatrix" : @[ @"(", @")"],
@"bmatrix" : @[ @"[", @"]"],
@"Bmatrix" : @[ @"{", @"}"],
@"vmatrix" : @[ @"vert", @"vert"],
@"Vmatrix" : @[ @"Vert", @"Vert"], };
}
});
if ([matrixEnvs objectForKey:env]) {
// it is set to matrix as the delimiters are converted to latex outside the table.
table.environment = @"matrix";
Expand Down Expand Up @@ -493,7 +520,8 @@ + (nullable MTMathAtom *)tableWithEnvironment:(NSString *)env rows:(NSArray<NSAr
+ (NSMutableDictionary<NSString*, MTMathAtom*>*) supportedLatexSymbols
{
static NSMutableDictionary<NSString*, MTMathAtom*>* commands = nil;
if (!commands) {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
commands = [NSMutableDictionary dictionaryWithDictionary:@{
// Greek characters
@"alpha" : [MTMathAtom atomWithType:kMTMathAtomVariable value:@"\u03B1"],
Expand Down Expand Up @@ -883,15 +911,15 @@ + (nullable MTMathAtom *)tableWithEnvironment:(NSString *)env rows:(NSArray<NSAr
@"scriptstyle" : [[MTMathStyle alloc] initWithStyle:kMTLineStyleScript],
@"scriptscriptstyle" : [[MTMathStyle alloc] initWithStyle:kMTLineStyleScriptScript],
}];

}
});
return commands;
}

+ (NSDictionary*) aliases
{
static NSDictionary* aliases = nil;
if (!aliases) {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
aliases = @{
@"lnot" : @"neg",
@"land" : @"wedge",
Expand Down Expand Up @@ -920,14 +948,15 @@ + (NSDictionary*) aliases
@"precnapprox" : @"nprecapprox",
@"succnapprox" : @"nsuccapprox",
};
}
});
return aliases;
}

+ (NSMutableDictionary<NSString*, NSMutableDictionary<NSNumber*, NSString*>*>*) textToLatexSymbolNames
{
static NSMutableDictionary<NSString*, NSMutableDictionary<NSNumber*, NSString*>*>* textToCommands = nil;
if (!textToCommands) {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
NSDictionary* commands = [self supportedLatexSymbols];
textToCommands = [NSMutableDictionary dictionaryWithCapacity:commands.count];
for (NSString* command in commands) {
Expand Down Expand Up @@ -957,14 +986,15 @@ + (NSDictionary*) aliases
}
inner[typeKey] = command;
}
}
});
return textToCommands;
}

+ (NSDictionary<NSString*, NSString*>*) accents
{
static NSDictionary* accents = nil;
if (!accents) {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
accents = @{
@"grave" : @"\u0300",
@"acute" : @"\u0301",
Expand All @@ -979,14 +1009,15 @@ + (NSDictionary*) aliases
@"widehat" : @"\u0302",
@"widetilde" : @"\u0303",
};
}
});
return accents;
}

+ (NSDictionary*) accentValueToName
{
static NSDictionary* accentToCommands = nil;
if (!accentToCommands) {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
NSDictionary* accents = [self accents];
NSMutableDictionary* mutableDict = [NSMutableDictionary dictionaryWithCapacity:accents.count];
for (NSString* command in accents) {
Expand All @@ -1007,14 +1038,15 @@ + (NSDictionary*) accentValueToName
mutableDict[acc] = command;
}
accentToCommands = [mutableDict copy];
}
});
return accentToCommands;
}

+(NSDictionary<NSString*, NSString*> *) delimiters
{
static NSDictionary* delims = nil;
if (!delims) {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
delims = @{
@"." : @"", // . means no delimiter
@"(" : @"(",
Expand Down Expand Up @@ -1049,14 +1081,15 @@ + (NSDictionary*) accentValueToName
@"lfloor" : @"\u230A",
@"rfloor" : @"\u230B",
};
}
});
return delims;
}

+ (NSDictionary*) delimValueToName
{
static NSDictionary* delimToCommands = nil;
if (!delimToCommands) {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
NSDictionary* delims = [self delimiters];
NSMutableDictionary* mutableDict = [NSMutableDictionary dictionaryWithCapacity:delims.count];
for (NSString* command in delims) {
Expand All @@ -1077,15 +1110,16 @@ + (NSDictionary*) delimValueToName
mutableDict[delim] = command;
}
delimToCommands = [mutableDict copy];
}
});
return delimToCommands;
}


+(NSDictionary<NSString*, NSNumber*> *) fontStyles
{
static NSDictionary<NSString*, NSNumber*>* fontStyles = nil;
if (!fontStyles) {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
// \text* commands are handled by the parser via the textStyles
// dictionary, so they do NOT appear here.
fontStyles = @{
Expand All @@ -1106,7 +1140,7 @@ + (NSDictionary*) delimValueToName
@"mathbfit": @(kMTFontStyleBoldItalic),
@"bm": @(kMTFontStyleBoldItalic),
};
}
});
return fontStyles;
}

Expand All @@ -1115,7 +1149,8 @@ + (NSDictionary*) delimValueToName
+ (NSDictionary<NSString*, MTMathStackCommandSpec*>*) stackCommands
{
static NSDictionary* stackCommands = nil;
if (!stackCommands) {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
// Each command maps to a single stretchy cap glyph (a Unicode codepoint). The
// typesetter walks the cap's OpenType h_variants first; if no variant is wide
// enough, it falls back to the font's HorizontalGlyphAssembly (parts + connector
Expand All @@ -1142,7 +1177,7 @@ + (NSDictionary*) delimValueToName
@"stackrel": [[MTMathStackCommandSpec alloc] initWithOver:nil under:nil displayClass:kMTMathAtomRelation argRoles:@[@(kMTStackArgOver), @(kMTStackArgBase)] inheritsClass:NO],
@"stackbin": [[MTMathStackCommandSpec alloc] initWithOver:nil under:nil displayClass:kMTMathAtomBinaryOperator argRoles:@[@(kMTStackArgOver), @(kMTStackArgBase)] inheritsClass:NO],
};
}
});
return stackCommands;
}

Expand Down Expand Up @@ -1192,7 +1227,8 @@ + (MTMathAtomType) inheritedDisplayClassForBase:(MTMathList*)base
+ (NSDictionary<NSString*, NSString*>*) stackCommandReverseTable
{
static NSDictionary* reverseTable = nil;
if (!reverseTable) {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
NSDictionary<NSString*, MTMathStackCommandSpec*>* forward = [self stackCommands];
NSMutableDictionary* mutable = [NSMutableDictionary dictionaryWithCapacity:forward.count];
for (NSString* cmd in forward) {
Expand All @@ -1201,7 +1237,7 @@ + (MTMathAtomType) inheritedDisplayClassForBase:(MTMathList*)base
mutable[key] = cmd;
}
reverseTable = [mutable copy];
}
});
return reverseTable;
}

Expand Down
20 changes: 12 additions & 8 deletions iosMath/lib/MTMathListBuilder.m
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Original file line number Diff line number Diff line change
Expand Up @@ -607,10 +607,11 @@ - (BOOL) expectCharacter:(unichar) ch
- (NSString*) readCommand
{
static NSSet<NSNumber*>* singleCharCommands = nil;
if (!singleCharCommands) {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
NSArray* singleChars = @[ @'{', @'}', @'$', @'#', @'%', @'_', @'|', @' ', @',', @'>', @';', @'!', @'\\' ];
singleCharCommands = [[NSSet alloc] initWithArray:singleChars];
}
});
if ([self hasCharacters]) {
// Check if we have a single character command.
unichar ch = [self getNextCharacter];
Expand Down Expand Up @@ -848,13 +849,14 @@ - (MTMathAtom*) atomForCommand:(NSString*) command
- (MTMathList*) stopCommand:(NSString*) command list:(MTMathList*) list stopChar:(unichar) stopChar
{
static NSDictionary<NSString*, NSArray*>* fractionCommands = nil;
if (!fractionCommands) {
static dispatch_once_t fractionCommandsOnce;
dispatch_once(&fractionCommandsOnce, ^{
fractionCommands = @{ @"over" : @[],
@"atop" : @[],
@"choose" : @[ @"(", @")"],
@"brack" : @[ @"[", @"]"],
@"brace" : @[ @"{", @"}"]};
}
});
if ([command isEqualToString:@"right"]) {
if (!_currentInnerAtom) {
NSString* errorMessage = @"Missing \\left";
Expand Down Expand Up @@ -1009,7 +1011,8 @@ - (MTMathAtom*) buildTable:(NSString*) env firstList:(MTMathList*) firstList row
+ (NSDictionary*) spaceToCommands
{
static NSDictionary* spaceToCommands = nil;
if (!spaceToCommands) {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
spaceToCommands = @{
@3 : @",",
@4 : @">",
Expand All @@ -1018,7 +1021,7 @@ + (NSDictionary*) spaceToCommands
@18 : @"quad",
@36 : @"qquad",
};
}
});
return spaceToCommands;
}

Expand Down Expand Up @@ -1093,14 +1096,15 @@ + (NSDictionary*) spaceToCommands
+ (NSDictionary*) styleToCommands
{
static NSDictionary* styleToCommands = nil;
if (!styleToCommands) {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
styleToCommands = @{
@(kMTLineStyleDisplay) : @"displaystyle",
@(kMTLineStyleText) : @"textstyle",
@(kMTLineStyleScript) : @"scriptstyle",
@(kMTLineStyleScriptScript) : @"scriptscriptstyle",
};
}
});
return styleToCommands;
}

Expand Down
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