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lib: Fix infinite loop on paths with nested links #61391

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lib: Fix infinite loop on paths with nested links #61391

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2914f1e
lib: fix infinite loop in fs.realpathSync
mattskel Dec 15, 2025
44be9f0
lib: fix infinite loop in fs.realpathSync
mattskel Jan 16, 2026
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34 changes: 28 additions & 6 deletions lib/fs.js
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Original file line number Diff line number Diff line change
Expand Up @@ -2730,17 +2730,29 @@ function realpathSync(p, options) {
// Walk down the path, swapping out linked path parts for their real
// values
// NB: p.length changes.
while (pos < p.length) {
// find the next part
const result = nextPart(p, pos);
let unresolvedTail = '';
while (true) {
if (pos >= p.length) {
if (unresolvedTail === '') {
break;
}

p = pathModule.resolve(p + unresolvedTail);
unresolvedTail = '';
current = base = splitRoot(p);
pos = current.length;
continue;
}

const result = nextPart(p + unresolvedTail, pos);
previous = current;
if (result === -1) {
const last = StringPrototypeSlice(p, pos);
current += last;
base = previous + last;
pos = p.length;
} else {
current += StringPrototypeSlice(p, pos, result + 1);
current += StringPrototypeSlice(p + unresolvedTail, pos, result + 1);
base = previous + StringPrototypeSlice(p, pos, result);
pos = result + 1;
}
Expand All @@ -2761,7 +2773,6 @@ function realpathSync(p, options) {
} else {
// Use stats array directly to avoid creating an fs.Stats instance just
// for our internal use.

const stats = binding.lstat(base, true, undefined, true /* throwIfNoEntry */);
if (stats === undefined) {
return;
Expand All @@ -2770,6 +2781,11 @@ function realpathSync(p, options) {
if (!isFileType(stats, S_IFLNK)) {
knownHard.add(base);
cache?.set(base, base);
if (unresolvedTail !== '') {
p = pathModule.resolve(p + unresolvedTail);
unresolvedTail = '';
}

continue;
}

Expand All @@ -2789,8 +2805,14 @@ function realpathSync(p, options) {
binding.stat(base, false, undefined, true);
linkTarget = binding.readlink(base, undefined);
}
resolvedLink = pathModule.resolve(previous, linkTarget);

const nextPathDelimiterIndex = nextPart(linkTarget, 0);
if (nextPathDelimiterIndex >= 1) {
unresolvedTail = StringPrototypeSlice(linkTarget, nextPathDelimiterIndex) + unresolvedTail;
linkTarget = StringPrototypeSlice(linkTarget, 0, nextPathDelimiterIndex);
}

resolvedLink = pathModule.resolve(previous, linkTarget);
cache?.set(base, resolvedLink);
if (!isWindows) seenLinks.set(id, linkTarget);
}
Expand Down