git: 7db725b25ed9 - stable/15 - proc_set_cred(): Allow 'newcred' to have multiple references

The branch stable/15 has been updated by olce:

URL: https://cgit.FreeBSD.org/src/commit/?id=7db725b25ed933b5e126386652e801c8fed34a84

commit 7db725b25ed933b5e126386652e801c8fed34a84
Author:     Olivier Certner <olce@FreeBSD.org>
AuthorDate: 2025-11-06 22:25:57 +0000
Commit:     Olivier Certner <olce@FreeBSD.org>
CommitDate: 2026-01-06 13:33:24 +0000

    proc_set_cred(): Allow 'newcred' to have multiple references
    
    This is an extension needed by next commit, where some additional
    reference is kept on the credentials to be set on a process in order to
    keep these credentials alive even after the process lock is released (an
    intervening reset of process credentials could release the reference
    that the process holds).
    
    Only 'cr_users' is incremented, as the reference (counted in 'cr_ref')
    comes from the caller, who passes it to the process.
    
    Reviewed by:    kib, markj
    MFC after:      1 week
    Sponsored by:   The FreeBSD Foundation
    Differential Revision:  https://reviews.freebsd.org/D53636
    
    (cherry picked from commit 5d46d11772c3280fd1c8ae09f20ce6c57f631c30)
---
 sys/kern/kern_prot.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/sys/kern/kern_prot.c b/sys/kern/kern_prot.c
index 0b7dc2169335..30cc617ceaf1 100644
--- a/sys/kern/kern_prot.c
+++ b/sys/kern/kern_prot.c
@@ -2792,10 +2792,6 @@ _proc_set_cred(struct proc *p, struct ucred *newcred, bool enforce_proc_lim)
 
 	MPASS(oldcred != NULL);
 	PROC_LOCK_ASSERT(p, MA_OWNED);
-	KASSERT(newcred->cr_users == 0, ("%s: users %d not 0 on cred %p",
-	    __func__, newcred->cr_users, newcred));
-	KASSERT(newcred->cr_ref == 1, ("%s: ref %ld not 1 on cred %p",
-	    __func__, newcred->cr_ref, newcred));
 
 	if (newcred->cr_ruidinfo != oldcred->cr_ruidinfo) {
 		/*
@@ -2821,8 +2817,10 @@ _proc_set_cred(struct proc *p, struct ucred *newcred, bool enforce_proc_lim)
 	    __func__, oldcred->cr_users, oldcred));
 	oldcred->cr_users--;
 	mtx_unlock(&oldcred->cr_mtx);
+	mtx_lock(&newcred->cr_mtx);
+	newcred->cr_users++;
+	mtx_unlock(&newcred->cr_mtx);
 	p->p_ucred = newcred;
-	newcred->cr_users = 1;
 	PROC_UPDATE_COW(p);
 	if (newcred->cr_ruidinfo != oldcred->cr_ruidinfo)
 		(void)chgproccnt(oldcred->cr_ruidinfo, -1, 0);