Re: [musl] synccall patches

[Markus Wichmann <nullplan@gmx.net>]

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Hi all,

as discussed, I'm attaching a new patch for the __setxid issue.

Ciao,
Markus

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From 1f3b01f625dd7d33a7107efbd8417857461bb4fe Mon Sep 17 00:00:00 2001
From: Markus Wichmann <nullplan@gmx.net>
Date: Thu, 2 Nov 2023 17:39:33 +0100
Subject: [PATCH 4/4] Ensure valid setxid return value.

If __synccall() fails to capture all threads because tkill fails for
some reason other than EAGAIN, then the callback given will never be
executed, so nothing will ever overwrite the initial value. So that is
the value that will be returned from the function. The previous setting
of 1 is not a valid value for setuid() et al. to return.

I chose -EAGAIN since I don't know the reason the synccall failed ahead
of time, but EAGAIN is a specified error code for a possibly temporary
failure in setuid().
---
 src/unistd/setxid.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/unistd/setxid.c b/src/unistd/setxid.c
index 487c1a16..1dfb2c01 100644
--- a/src/unistd/setxid.c
+++ b/src/unistd/setxid.c
@@ -30,5 +30,5 @@ int __setxid(int nr, int id, int eid, int sid)
 	 * trigger the safety kill above. */
 	struct ctx c = { .nr = nr, .id = id, .eid = eid, .sid = sid, .ret = 1 };
 	__synccall(do_setxid, &c);
-	return __syscall_ret(c.ret);
+	return __syscall_ret(c.ret > 0? -EAGAIN : c.ret);
 }
--
2.39.2