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Date: Wed, 29 Jan 2020 12:20:07 +0100
From: Sören Tempel <>
Subject: [PATCH v2] cuserid: support invocation with a NULL pointer argument

I did not manage to find a copy of IEEE 1003.1-1988 (the last POSIX
version where cuserid was last standardized) the Single UNIX
specification version 2 does state the following though [1]:

	If s is a null pointer, this representation is generated in an
	area that may be static (and thus overwritten by subsequent
	calls to cuserid()), the address of which is returned.

Even though this a legacy function it would therefore be nice for musl
to support usage with a NULL pointer. I ran into this on Alpine Linux
when using cdparanoia [2] which uses cuserid like this and therefore
caused a crash on my system.

 src/legacy/cuserid.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/legacy/cuserid.c b/src/legacy/cuserid.c
index 4e78798d..fd7832e4 100644
--- a/src/legacy/cuserid.c
+++ b/src/legacy/cuserid.c
@@ -5,10 +5,12 @@
 char *cuserid(char *buf)
+	static char usridbuf[L_cuserid];
 	struct passwd pw, *ppw;
 	long pwb[256];
 	if (getpwuid_r(geteuid(), &pw, (void *)pwb, sizeof pwb, &ppw))
 		return 0;
+	if (!buf) buf = usridbuf;
 	snprintf(buf, L_cuserid, "%s", pw.pw_name);
 	return buf;

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