git: eff554d9f3d6 - releng/15.0 - unix/stream: plug a corner case when control externalization failed

The branch releng/15.0 has been updated by markj:

URL: https://cgit.FreeBSD.org/src/commit/?id=eff554d9f3d6372c9cbb8ea315f910b81bd44eee

commit eff554d9f3d6372c9cbb8ea315f910b81bd44eee
Author:     Gleb Smirnoff <glebius@FreeBSD.org>
AuthorDate: 2025-10-15 20:01:25 +0000
Commit:     Mark Johnston <markj@FreeBSD.org>
CommitDate: 2026-08-24 19:29:47 +0000

    unix/stream: plug a corner case when control externalization failed
    
    while peer has closed its end.
    
    Approved by:    so
    Security:       FreeBSD-SA-26:57.unix
    Reported by:    syzbot+ffcc3612ea266e36604e@syzkaller.appspotmail.com
    
    (cherry picked from commit 4548b9f3a8167a340a5086ed51a76d932c9ab3cc)
    (cherry picked from commit e7070407aa8eae85bc412b9fd80865628b69f22d)
---
 sys/kern/uipc_usrreq.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/sys/kern/uipc_usrreq.c b/sys/kern/uipc_usrreq.c
index ecf7218f2ca3..932bda8b568d 100644
--- a/sys/kern/uipc_usrreq.c
+++ b/sys/kern/uipc_usrreq.c
@@ -1552,15 +1552,19 @@ restart:
 				mc_init_m(&cmc, control);
 
 				SOCK_RECVBUF_LOCK(so);
-				MPASS(!(sb->sb_state & SBS_CANTRCVMORE));
-
-				if (__predict_false(cmc.mc_len + sb->sb_ccc +
-				    sb->sb_ctl > sb->sb_hiwat)) {
+				if (__predict_false(
+				    (sb->sb_state & SBS_CANTRCVMORE) ||
+				    cmc.mc_len + sb->sb_ccc + sb->sb_ctl >
+				    sb->sb_hiwat)) {
 					/*
-					 * Too bad, while unp_externalize() was
-					 * failing, the other side had filled
-					 * the buffer and we can't prepend data
-					 * back. Losing data!
+					 * While the lock was dropped and we
+					 * were failing in unp_externalize(),
+					 * the peer could has a) disconnected,
+					 * b) filled the buffer so that we
+					 * can't prepend data back.
+					 * These are two edge conditions that
+					 * we just can't handle, so lose the
+					 * data and return the error.
 					 */
 					SOCK_RECVBUF_UNLOCK(so);
 					SOCK_IO_RECV_UNLOCK(so);