[PATCH] nproc: Verify the cgroup path isn't truncated.

[Collin Funk]

I don't think it is actually possible for this case to happen, but
checking it does no harm.

Lasse Collin mentioned it to me while we were discussing some cgroup
stuff a while ago.

-- 8< --

* lib/nproc.c (get_cgroup2_cpu_quota): Check the return value of
snprintf to make sure the path isn't truncated.
---
 ChangeLog   | 6 ++++++
 lib/nproc.c | 7 ++++---
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 65793e578c..d56394b482 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2026-08-15  Collin Funk  <collin.fu...@gmail.com>
+
+       nproc: Verify the cgroup path isn't truncated.
+       * lib/nproc.c (get_cgroup2_cpu_quota): Check the return value of
+       snprintf to make sure the path isn't truncated.
+
 2026-08-14  Bruno Haible  <br...@clisp.org>
 
        Add unit tests and doc for the %Lf large precision issue on Solaris.
diff --git a/lib/nproc.c b/lib/nproc.c
index ef86975fb1..e3dfeaa16d 100644
--- a/lib/nproc.c
+++ b/lib/nproc.c
@@ -437,10 +437,11 @@ get_cgroup2_cpu_quota (void)
          is not enabled for that part of the hierarchy.  */
 
       char cpu_max_file[PATH_MAX];
-      snprintf (cpu_max_file, sizeof (cpu_max_file),
-                "%s%s/cpu.max", mount, cgroup);
+      int n = snprintf (cpu_max_file, sizeof (cpu_max_file),
+                        "%s%s/cpu.max", mount, cgroup);
 
-      if ((fp = fopen (cpu_max_file, "r"))
+      if (0 <= n && n < sizeof cpu_max_file
+          && (fp = fopen (cpu_max_file, "r"))
           && getline (&quota_str, &quota_size, fp) != -1
           && strncmp (quota_str, "max", 3) != 0)
         {
-- 
2.55.0