linux-kernel - [PATCH] s390/extmem: Replace sprintf with snprintf for buffer safety

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Message-ID: <20251001191404.239217-1-hi@josie.lol>
Date: Wed,  1 Oct 2025 21:14:04 +0200
From: Josephine Pfeiffer <hi@...ie.lol>
To: Alexander Gordeev <agordeev@...ux.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
	Heiko Carstens <hca@...ux.ibm.com>,
	Vasily Gorbik <gor@...ux.ibm.com>,
	Christian Borntraeger <borntraeger@...ux.ibm.com>,
	Sven Schnelle <svens@...ux.ibm.com>,
	linux-s390@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] s390/extmem: Replace sprintf with snprintf for buffer safety

Replace unsafe sprintf() calls with snprintf() in segment_save() to
prevent potential buffer overflows. The function builds command strings
by repeatedly appending to a fixed-size buffer, which could overflow if
segment ranges are numerous or values are large.

Signed-off-by: Josephine Pfeiffer <hi@...ie.lol>
---
 arch/s390/mm/extmem.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/arch/s390/mm/extmem.c b/arch/s390/mm/extmem.c
index f7da53e212f5..b6464a322eb1 100644
--- a/arch/s390/mm/extmem.c
+++ b/arch/s390/mm/extmem.c
@@ -598,14 +598,16 @@ segment_save(char *name)
 		goto out;
 	}
 
-	sprintf(cmd1, "DEFSEG %s", name);
+	snprintf(cmd1, sizeof(cmd1), "DEFSEG %s", name);
 	for (i=0; i<seg->segcnt; i++) {
-		sprintf(cmd1+strlen(cmd1), " %lX-%lX %s",
-			seg->range[i].start >> PAGE_SHIFT,
-			seg->range[i].end >> PAGE_SHIFT,
-			segtype_string[seg->range[i].start & 0xff]);
+		size_t len = strlen(cmd1);
+
+		snprintf(cmd1 + len, sizeof(cmd1) - len, " %lX-%lX %s",
+			 seg->range[i].start >> PAGE_SHIFT,
+			 seg->range[i].end >> PAGE_SHIFT,
+			 segtype_string[seg->range[i].start & 0xff]);
 	}
-	sprintf(cmd2, "SAVESEG %s", name);
+	snprintf(cmd2, sizeof(cmd2), "SAVESEG %s", name);
 	response = 0;
 	cpcmd(cmd1, NULL, 0, &response);
 	if (response) {
-- 
2.51.0