V: enable stack usage guard by masatake · Pull Request #4387 · universal-ctags/ctags

masatake · 2026-02-21T15:36:13Z

Fixes #4369 (CVE-2026-2641)
Fixes #4409

Author: Masatake YAMATO [email protected]
Date: Fri Feb 20 04:23:04 2026 +0900

V: enable stack usage guard

Enable the stack usage guard in the V parser.

Partially fixes: #4369
Partially addresses: CVE-2026-2641

The default stack limit is 4MB.
It may need adjustment on platforms with smaller default
stack sizes. (WIP)

Signed-off-by: Masatake YAMATO <[email protected]>

Author: Masatake YAMATO [email protected]
Date: Fri Feb 20 04:22:45 2026 +0900

main: add stack usage guard

Introduce a stack usage guard to prevent stack overflow
in deeply nested input.
as
The default stack limit is currently 4MB.
It can be adjusted with the --stack-limit=<bytes> option.

This change adds the infrastructure in the main part.
Individual parsers must explicitly enable the guard
to benefit from stack protection.

Signed-off-by: Masatake YAMATO <[email protected]>

TODO:

codecov · 2026-02-23T07:20:49Z

Codecov Report

❌ Patch coverage is 79.16667% with 30 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.97%. Comparing base (76e4cc2) to head (f253e51).

Files with missing lines	Patch %	Lines
main/stackguard.c	88.46%	9 Missing ⚠️
parsers/jscript.c	25.00%	9 Missing ⚠️
main/options.c	80.00%	5 Missing ⚠️
parsers/v.c	28.57%	5 Missing ⚠️
main/entry.c	50.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4387      +/-   ##
==========================================
- Coverage   85.98%   85.97%   -0.02%     
==========================================
  Files         255      256       +1     
  Lines       63884    64023     +139     
==========================================
+ Hits        54931    55042     +111     
- Misses       8953     8981      +28

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Copilot

Pull request overview

Enables an opt-in stack usage guard to mitigate stack overflows during parsing (notably for the V parser), and adds a CLI option to configure the guard’s limit.

Changes:

Add stack guard infrastructure (main/stackguard.c, main/stackguard_p.h) and wire it into the parse loop via per-parser discardInput.
Enable the guard in the V parser and expose --stack-limit=<bytes> plus diagnostics (verbose + totals).
Update build files (make + VS project) and adjust expected outputs for updated diagnostics.

Reviewed changes

Copilot reviewed 18 out of 18 changed files in this pull request and generated 10 comments.

Show a summary per file

File	Description
win32/ctags_vs2013.vcxproj.filters	Adds stackguard sources/headers to VS filters for building on Windows.
win32/ctags_vs2013.vcxproj	Includes stackguard source/header in the VS project build.
source.mak	Adds stackguard source/header to the build lists for non-Windows builds.
parsers/v.c	Enables stack guard checks in an expression list parse path; provides parser-specific EOF discard function.
main/stats.c	Prints observed peak stack usage in totals output.
main/stackguard_p.h	Declares the stack guard API used by main/options/parse/stats.
main/stackguard.c	Implements stack tracking, limit handling, and peak usage tracking.
main/parse_p.h	Declares the query function for stack-guard support (typo present).
main/parse.h	Adds `discardInputFn` hook and exposes `stackGuardCheck` to parsers.
main/parse.c	Prepares/releases stack guard around parser execution; adds support query function (typo present).
main/options.c	Adds `--stack-limit` option and prints “stack guard supported/unsupported” in language description; updates some error messages.
main/main.c	Logs the computed stack limit in verbose mode.
configure.ac	Detects `sys/resource.h` for `getrlimit`-based default limit computation.
Tmain/versioning.d/stdout-expected.txt	Updates expected “describe language” output for “stack guard” line.
Tmain/broken-tagname.d/stderr-expected.txt	Updates expected verbose output to include stack limit line.
Tmain/broken-tagname.d/run.sh	Adds `--stack-limit=8192` to stabilize verbose output and adjusts sed formatting.
Tmain/broken-tagname-in-ectags-format.d/stderr-expected.txt	Updates expected verbose output to include stack limit line.
Tmain/broken-tagname-in-ectags-format.d/run.sh	Adds `--stack-limit=8192` to stabilize verbose output.

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Copilot · 2026-02-23T07:25:38Z

+	if (!stackGuardCheck(token))
+		return;


This introduces new control-flow behavior (early return + EOF discard) when the stack limit is exceeded, but the PR description lists 'add test cases' as TODO and the current diffs only stabilize verbose output tests. Add an integration test that forces deep nesting in V input (or a dedicated selftest parser case) to assert: (1) a NOTICE is emitted about exceeding the limit, and (2) parsing terminates safely without crashing/hanging.

Signed-off-by: Masatake YAMATO <[email protected]>

…help message at runtime Signed-off-by: Masatake YAMATO <[email protected]>

masatake · 2026-05-06T21:51:14Z

The DTS parser looks broken.
When processing the Linux source tree, 32, the limit defined in 7a35227 causes many notice messages.

masatake · 2026-05-06T22:05:07Z

ulimit based test may not work on Windows.

Introduce a stack usage guard to prevent stack overflow in deeply nested input. The default stack limit is derived from the value returned by getrlimit(RLIMIT_STACK). On platforms where getrlimit() is not available, a default limit of about 1MB is used, with a 32kB safety margin reserved. The limit can be adjusted with the --stack-limit=<bytes> option. The --verbose option prints the stack limit actually used: $ ./ctags --help ... --stack-limit=<bytes> Limit the stack usage while parsing, in bytes [8372224]. $ ./ctags --stack-limit=81920 --help ... --stack-limit=<bytes> Limit the stack usage while parsing, in bytes [81920]. ... The --totals option prints the observed peak stack usage: $ ./ctags --totals -o - main/main.c > /dev/null 1 file, 612 lines (13 kB) scanned in 0.0 seconds (4710 kB/s) 20 tags added to tag file 20 tags sorted in 0.00 seconds Observed peak stack usage: 4096 bytes (4.0 KiB) This change introduces the infrastructure in the main part. Individual parsers must explicitly enable the guard to benefit from stack protection. Signed-off-by: Masatake YAMATO <[email protected]>

Signed-off-by: Masatake YAMATO <[email protected]>

… user mode Signed-off-by: Masatake YAMATO <[email protected]>

Partially fixes: universal-ctags#4369 Partially addresses: CVE-2026-2641 Signed-off-by: Masatake YAMATO <[email protected]>

The stack guard limits the recursion in parsing. I found the stack guard is not enough to use ctags with bad input. If parser->requestAutomaticFQTag is enabled, ctags fills scope field of tags automatically based on cork indexes signed to scopeIndex member of tagEntryInfo. If the scope is too deep, filling takes too long time. This change limits the depth of scope to 32. Unlike the stack guard, I hard-coded to limit. Signed-off-by: Masatake YAMATO <[email protected]>

Fixes: universal-ctags#4409 Signed-off-by: Masatake YAMATO <[email protected]>

masatake · 2026-05-07T22:04:24Z

Cygwin:

/home/runner/work/ctags/ctags/Tmain/stack-guard-option.d/stdout-diff.txt

	--- ./Tmain/stack-guard-option.d/stdout-expected.txt	2026-05-07 19:40:59.220998901 +0000
	+++ /home/runner/work/ctags/ctags/Tmain/stack-guard-option.d/stdout-actual.txt	2026-05-07 19:42:54.339347000 +0000
	@@ -3,2 +2,0 @@
	-Notice: call stack exceeds the limit (LIMIT) during processing input: input.v
	-qnCmeoduen	input.v	/^moluleptt b); assi9223372036854775n b const qnCmeoduen=$/;"	c
	@@ -11,2 +8,0 @@
	-Notice: call stack exceeds the limit (LIMIT) during processing input: input.v
	-qnCmeoduen	input.v	/^moluleptt b); assi9223372036854775n b const qnCmeoduen=$/;"	c
	@@ -19 +14,0 @@
	-Warning: don't specify stack limit larger than default: 32769 > 32768
	@@ -22,0 +18,4 @@
	+# ulimit(HELP): 64, no option
	+  --stack-limit=<bytes>
	+       Limit the stack usage while parsing, in bytes [18446744073709518847].
	+
	@@ -24,2 +22,0 @@
	-Notice: call stack exceeds the limit (LIMIT) during processing input: input.js
	-f0	input.js	/^var f0 = function(LIMIT) {$/;"	f

/home/runner/work/ctags/ctags/Tmain/stack-guard-option.d/stderr-diff.txt

	--- ./Tmain/stack-guard-option.d/stderr-expected.txt	2026-05-07 19:40:59.220998901 +0000
	+++ /home/runner/work/ctags/ctags/Tmain/stack-guard-option.d/stderr-actual.txt	2026-05-07 19:42:54.339376000 +0000
	@@ -0,0 +1,3 @@
	+Segmentation fault (core dumped)
	+Segmentation fault (core dumped)
	+Segmentation fault (core dumped)

FreeBSD:

	--- ./Tmain\stack-guard-option.d/stdout-expected.txt	2026-05-07 19:41:48.388036100 +0000
	+++ D:/a/ctags/ctags/Tmain/stack-guard-option.d/stdout-actual.txt	2026-05-07 19:48:39.894513000 +0000
	@@ -19 +18,0 @@
	-Warning: don't specify stack limit larger than default: 32769 > 32768
	@@ -21,0 +21,4 @@
	+
	+# ulimit(HELP): 64, no option
	+  --stack-limit=<bytes>
	+       Limit the stack usage while parsing, in bytes [2048000].

ctags on both platforms use getrlimit.

masatake · 2026-05-12T19:23:46Z

+	{
+		rlim_t cur = rlim.rlim_cur;
+
+		if (rlim.rlim_cur == RLIM_INFINITY || cur > (rlim_t) SIZE_MAX)


The way to handle RLIM_INFINITY is completely wrong.
If a user specifies RLIM_INFINITY (via ulimit -s), ctags should disable the stack usage guard.

masatake force-pushed the V--CVE-2026-2641 branch from 4ea70eb to e1546c1 Compare February 23, 2026 07:13

masatake requested a review from Copilot February 23, 2026 07:18

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masatake force-pushed the V--CVE-2026-2641 branch 3 times, most recently from f70ab53 to 7cd2d3a Compare February 26, 2026 16:19

masatake force-pushed the V--CVE-2026-2641 branch 4 times, most recently from 08e746e to dc4393b Compare March 22, 2026 23:25

masatake mentioned this pull request Mar 27, 2026

[WIP] main: oneshot mode, reading source file contents from stdin #4407

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5 tasks

masatake marked this pull request as draft March 30, 2026 08:51

masatake force-pushed the V--CVE-2026-2641 branch from dc4393b to cc96186 Compare April 1, 2026 02:05

masatake mentioned this pull request Apr 1, 2026

JavaScript parser can crash or exhaust memory with deeply nested functions #4409

Open

masatake force-pushed the V--CVE-2026-2641 branch 2 times, most recently from a038815 to 5df0ca9 Compare May 3, 2026 21:16

masatake added 5 commits May 4, 2026 06:18

main: delete a redundant empty line

2764d05

Signed-off-by: Masatake YAMATO <[email protected]>

main: show the help message for --quiet option even in etags mode

bbabd6b

Signed-off-by: Masatake YAMATO <[email protected]>

main: revise the help message for --pattern-length-limit option

2290941

Signed-off-by: Masatake YAMATO <[email protected]>

main: allow to arrange the help message for options at runtume

3912170

Signed-off-by: Masatake YAMATO <[email protected]>

main: add the default value for --pattern-length-limit option to its …

2afe0b2

…help message at runtime Signed-off-by: Masatake YAMATO <[email protected]>

masatake force-pushed the V--CVE-2026-2641 branch 3 times, most recently from 56ee44b to 2043dca Compare May 6, 2026 21:49

masatake added 2 commits May 7, 2026 19:09

main: implement the dynamic-stack-guard for win32

b474f3c

Signed-off-by: Masatake YAMATO <[email protected]>

masatake added 2 commits May 7, 2026 19:19

docs(man): write about --stack-limit option

97c6c54

Signed-off-by: Masatake YAMATO <[email protected]>

docs(web): write about the stackGuardCheck() to the hacking guide

b921f58

Signed-off-by: Masatake YAMATO <[email protected]>

masatake force-pushed the V--CVE-2026-2641 branch 2 times, most recently from 4bf2fdd to 6fa47df Compare May 7, 2026 13:55

masatake added 5 commits May 8, 2026 04:35

Tmain: add a helper function for skipping running a test case on Qemu…

b209041

… user mode Signed-off-by: Masatake YAMATO <[email protected]>

V: enable stack usage guard

9a276e3

Partially fixes: universal-ctags#4369 Partially addresses: CVE-2026-2641 Signed-off-by: Masatake YAMATO <[email protected]>

JavaScript: enable stack usage guard

72b0266

Fixes: universal-ctags#4409 Signed-off-by: Masatake YAMATO <[email protected]>

TEMP

09484ef

masatake force-pushed the V--CVE-2026-2641 branch from 6fa47df to 09484ef Compare May 7, 2026 19:37

masatake commented May 12, 2026

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