[PATCH] xargs: make errno handling after execvp failure more robust

[Bernhard Voelker]

I don't have a reproducer, but by reading of the code it was clear
that write() and close() before error() could eventually clobber the
errno value from execvp().

Pushed the attached.

Have a nice day,
Berny
From dd594fe7b83f4d0096a3d9a903b3abe6a3f4fb2e Mon Sep 17 00:00:00 2001
From: Bernhard Voelker <m...@bernhard-voelker.de>
Date: Mon, 23 Feb 2026 23:02:08 +0100
Subject: [PATCH] xargs: make errno handling after execvp failure more robust

* xargs/xargs.c (xargs_do_exec): Save errno in a new variable to avoid
that write() or close() clobber it before its value is used in error().
---
 xargs/xargs.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/xargs/xargs.c b/xargs/xargs.c
index 262a64cf..b7f8f1e8 100644
--- a/xargs/xargs.c
+++ b/xargs/xargs.c
@@ -1348,7 +1348,8 @@ xargs_do_exec (struct buildcmd_control *ctl, void *usercontext, int argc, char *
               errno = E2BIG;
             else
               execvp (argv[0], argv);
-            if (errno)
+            int saved_errno = errno;
+            if (saved_errno)
               {
                 /* Write errno value to parent.  We do this even if
                  * the error was not E2BIG, because we need to
@@ -1362,19 +1363,21 @@ xargs_do_exec (struct buildcmd_control *ctl, void *usercontext, int argc, char *
                  * utility if we run it, for POSIX compliance on the
                  * handling of exit values.
                  */
-                write (fd[1], &errno, sizeof (int));
+                write (fd[1], &saved_errno, sizeof (int));
               }
 
             close (fd[1]);
-            if (E2BIG != errno)
+            if (E2BIG != saved_errno)
               {
-                error (0, errno, _("failed to run command %s"),
+                error (0, saved_errno, _("failed to run command %s"),
                        quotearg_n_style (0, locale_quoting_style, argv[0]));
               }
             /* The actual value returned here should be irrelevant,
              * because the parent will test our value of errno.
              */
-            _exit (errno == ENOENT ? XARGS_EXIT_COMMAND_NOT_FOUND : XARGS_EXIT_COMMAND_CANNOT_BE_RUN);
+            _exit (saved_errno == ENOENT
+                     ? XARGS_EXIT_COMMAND_NOT_FOUND
+                     : XARGS_EXIT_COMMAND_CANNOT_BE_RUN);
 
           /*NOTREACHED*/
           } /* child */
-- 
2.52.0