[PATCH net] ptp: limit number of virtual clocks per physical clock

[PATCH net] ptp: limit number of virtual clocks per physical clock

[Thomas Weißschuh]

The sysfs interface can be used to trigger arbitrarily large memory
allocations. This can induce pressure on the VM layer to satisfy the
request only to fail anyways.

Reported-by: cheung wall <zzqq0103.hey@gmail.com>
Closes: https://lore.kernel.org/lkml/20250103091906.GD1977892@ZenIV/
Fixes: 73f37068d540 ("ptp: support ptp physical/virtual clocks conversion")
Cc: stable@vger.kernel.org
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
The limit is completely made up, let me know if there is something
better.

I'm also wondering about the point of the max_vclocks sysfs attribute.
It could easily be removed and all its logic moved into the n_vclocks
attribute, simplifying the UAPI.
---
 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 18934e28469ee6e3bf9c9e6d1a1adb82808d88e6..07003339795e9c0fb813887e47eaee4ba0e20064 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 2048
 #define PTP_MAX_CHANNELS 2048
 
 struct timestamp_event_queue {
diff --git a/drivers/ptp/ptp_sysfs.c b/drivers/ptp/ptp_sysfs.c
index 6b1b8f57cd9510f269c86dd89a7a74f277f6916b..200eaf50069681eecc87d63c0e0440f28cccab77 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)

---
base-commit: 582ef8a0c406e0b17030b0773392595ec331a0d2
change-id: 20250103-ptp-max_vclocks-0dab5b03b006

Best regards,
-- 
Thomas Weißschuh <linux@weissschuh.net>

Re: [PATCH net] ptp: limit number of virtual clocks per physical clock

[Paolo Abeni]

On 1/3/25 2:40 PM, Thomas Weißschuh wrote:
> The sysfs interface can be used to trigger arbitrarily large memory
> allocations. This can induce pressure on the VM layer to satisfy the
> request only to fail anyways.
> 
> Reported-by: cheung wall <zzqq0103.hey@gmail.com>
> Closes: https://lore.kernel.org/lkml/20250103091906.GD1977892@ZenIV/
> Fixes: 73f37068d540 ("ptp: support ptp physical/virtual clocks conversion")
> Cc: stable@vger.kernel.org
> Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> ---
> The limit is completely made up, let me know if there is something
> better.

I'm also unsure if such constant value is reasonable for all the
use-cases. Any additional feedback more than welcome.

In any case, I guess it would make sense to update
Documentation/ABI/testing/sysfs-ptp accordingly.

Thanks,

Paolo