linux-kernel - [RFC PATCH net v2] ptp: Add a hard upper bound on max

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Message-ID: <20250923160622.8096-1-viswanathiyyappan@gmail.com>
Date: Tue, 23 Sep 2025 21:36:22 +0530
From: I Viswanath <viswanathiyyappan@...il.com>
To: richardcochran@...il.com,
	andrew+netdev@...n.ch,
	davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com
Cc: netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	skhan@...uxfoundation.org,
	linux-kernel-mentees@...ts.linux.dev,
	david.hunter.linux@...il.com,
	I Viswanath <viswanathiyyappan@...il.com>,
	syzbot+94d20db923b9f51be0df@...kaller.appspotmail.com
Subject: [RFC PATCH net v2] ptp: Add a hard upper bound on max_vclocks

syzbot reported WARNING in max_vclocks_store.

This occurs when the argument max is too large for kcalloc to handle.

Extend the guard to guard against values that are too large for
kcalloc

What would be a reasonable value for PTP_MAX_VCLOCKS_LIMIT?

KMALLOC_MAX_SIZE/(sizeof(int)) is the absolute max value for which the 
memory allocation wouldn't fail

Reported-by: syzbot+94d20db923b9f51be0df@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=94d20db923b9f51be0df
Tested-by: syzbot+94d20db923b9f51be0df@...kaller.appspotmail.com
Fixes: 73f37068d540 ("ptp: support ptp physical/virtual clocks conversion")
Signed-off-by: I Viswanath <viswanathiyyappan@...il.com>
---
v1:
Link: https://lore.kernel.org/linux-mm/20250922170357.148588-1-viswanathiyyappan@gmail.com/T/#u

v2:
- Moved the validation to max_vclocks_store

 drivers/ptp/ptp_private.h | 1 +
 drivers/ptp/ptp_sysfs.c   | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/ptp/ptp_private.h b/drivers/ptp/ptp_private.h
index b352df4cd3f9..f329263f33aa 100644
--- a/drivers/ptp/ptp_private.h
+++ b/drivers/ptp/ptp_private.h
@@ -22,6 +22,7 @@
 #define PTP_MAX_TIMESTAMPS 128
 #define PTP_BUF_TIMESTAMPS 30
 #define PTP_DEFAULT_MAX_VCLOCKS 20
+#define PTP_MAX_VCLOCKS_LIMIT (KMALLOC_MAX_SIZE/(sizeof(int)))
 #define PTP_MAX_CHANNELS 2048
 
 enum {
diff --git a/drivers/ptp/ptp_sysfs.c b/drivers/ptp/ptp_sysfs.c
index 6b1b8f57cd95..200eaf500696 100644
--- a/drivers/ptp/ptp_sysfs.c
+++ b/drivers/ptp/ptp_sysfs.c
@@ -284,7 +284,7 @@ static ssize_t max_vclocks_store(struct device *dev,
 	size_t size;
 	u32 max;
 
-	if (kstrtou32(buf, 0, &max) || max == 0)
+	if (kstrtou32(buf, 0, &max) || max == 0 || max > PTP_MAX_VCLOCKS_LIMIT)
 		return -EINVAL;
 
 	if (max == ptp->max_vclocks)
-- 
2.47.3