linux-kernel - [PATCH v2] s390/sclp: Add check for get_zeroed

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Message-Id: <20250218025216.2421548-1-haoxiang_li2024@163.com>
Date: Tue, 18 Feb 2025 10:52:16 +0800
From: Haoxiang Li <haoxiang_li2024@....com>
To: hca@...ux.ibm.com,
	gor@...ux.ibm.com,
	agordeev@...ux.ibm.com,
	borntraeger@...ux.ibm.com,
	svens@...ux.ibm.com,
	haoxiang_li2024@....com,
	schwidefsky@...ibm.com
Cc: linux-s390@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: [PATCH v2] s390/sclp: Add check for get_zeroed_page()

Add check for the return value of get_zeroed_page() in
sclp_console_init() to prevent null pointer dereference.
Furthermore, to solve the memory leak caused by the loop
allocation, add a free helper to do the free job.

Fixes: 4c8f4794b61e ("[S390] sclp console: convert from bootmem to slab")
Cc: stable@...r.kernel.org
Signed-off-by: Haoxiang Li <haoxiang_li2024@....com>
---
Changes in v2:
- Add a free helper to solve the memory leak caused by loop allocation.
- Thanks Heiko! I realized that v1 patch overlooked a potential memory leak.
After consideration, I choose to do the full exercise. I noticed a similar
handling in [1], following that handling I submit this v2 patch. Thanks again!

Reference link:
[1]https://github.com/torvalds/linux/blob/master/drivers/s390/char/sclp_vt220.c#L699
---
 drivers/s390/char/sclp_con.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/drivers/s390/char/sclp_con.c b/drivers/s390/char/sclp_con.c
index e5d947c763ea..c87b0c204718 100644
--- a/drivers/s390/char/sclp_con.c
+++ b/drivers/s390/char/sclp_con.c
@@ -263,6 +263,19 @@ static struct console sclp_console =
 	.index = 0 /* ttyS0 */
 };
 
+/*
+ *  Release allocated pages.
+ */
+static void __init __sclp_console_free_pages(void)
+{
+	struct list_head *page, *p;
+
+	list_for_each_safe(page, p, &sclp_con_pages) {
+		list_del(page);
+		free_page((unsigned long) page);
+	}
+}
+
 /*
  * called by console_init() in drivers/char/tty_io.c at boot-time.
  */
@@ -282,6 +295,10 @@ sclp_console_init(void)
 	/* Allocate pages for output buffering */
 	for (i = 0; i < sclp_console_pages; i++) {
 		page = (void *) get_zeroed_page(GFP_KERNEL | GFP_DMA);
+		if (!page) {
+			__sclp_console_free_pages();
+			return -ENOMEM;
+		}
 		list_add_tail(page, &sclp_con_pages);
 	}
 	sclp_conbuf = NULL;
-- 
2.25.1