linux-kernel - [PATCH] tools/nolibc: avoid error in dup2() if old fd equals new fd

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Message-Id: <20250819-nolibc-dup2-einval-v1-1-d6c8308cdc50@linutronix.de>
Date: Tue, 19 Aug 2025 09:26:19 +0200
From: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
To: Willy Tarreau <w@....eu>, 
 Thomas Weißschuh <linux@...ssschuh.net>, 
 "Paul E. McKenney" <paulmck@...nel.org>
Cc: linux-kernel@...r.kernel.org, 
 Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Subject: [PATCH] tools/nolibc: avoid error in dup2() if old fd equals new
 fd

dup2() allows both 'old' and 'new' to have the same value, which dup3()
does not. If libc dup2() is implemented through the dup3() system call,
then it would incorrectly fail in this case.

Avoid the error by handling old == new inside nolibc itself.

Fixes: 30ca20517ac1 ("tools headers: Move the nolibc header from rcutorture to tools/include/nolibc/")
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
---
 tools/include/nolibc/sys.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/include/nolibc/sys.h b/tools/include/nolibc/sys.h
index 295e71d34abadb7f9c7ca995012b4395b6830975..22a2e834861e618451ec678bd11101147dfa3a7d 100644
--- a/tools/include/nolibc/sys.h
+++ b/tools/include/nolibc/sys.h
@@ -238,6 +238,8 @@ static __attribute__((unused))
 int sys_dup2(int old, int new)
 {
 #if defined(__NR_dup3)
+	if (old == new)
+		return old;
 	return my_syscall3(__NR_dup3, old, new, 0);
 #elif defined(__NR_dup2)
 	return my_syscall2(__NR_dup2, old, new);

---
base-commit: 8f5ae30d69d7543eee0d70083daf4de8fe15d585
change-id: 20250819-nolibc-dup2-einval-825bfd77de7a

Best regards,
-- 
Thomas Weißschuh <thomas.weissschuh@...utronix.de>