net: napi: Prevent overflow of napi_defer_hard_irqs

In commit 6f8b12d661d0 ("net: napi: add hard irqs deferral feature")
napi_defer_irqs was added to net_device and napi_defer_irqs_count was
added to napi_struct, both as type int.

This value never goes below zero, so there is not reason for it to be a
signed int. Change the type for both from int to u32, and add an
overflow check to sysfs to limit the value to S32_MAX.

The limit of S32_MAX was chosen because the practical limit before this
patch was S32_MAX (anything larger was an overflow) and thus there are
no behavioral changes introduced. If the extra bit is needed in the
future, the limit can be raised.

Before this patch:

$ sudo bash -c 'echo 2147483649 > /sys/class/net/eth4/napi_defer_hard_irqs'
$ cat /sys/class/net/eth4/napi_defer_hard_irqs
-2147483647

After this patch:

$ sudo bash -c 'echo 2147483649 > /sys/class/net/eth4/napi_defer_hard_irqs'
bash: line 0: echo: write error: Numerical result out of range

Similarly, /sys/class/net/XXXXX/tx_queue_len is defined as unsigned:

include/linux/netdevice.h:      unsigned int            tx_queue_len;

And has an overflow check:

dev_change_tx_queue_len(..., unsigned long new_len):

  if (new_len != (unsigned int)new_len)
          return -ERANGE;

Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Joe Damato <jdamato@fastly.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20240904153431.307932-1-jdamato@fastly.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 5 insertions, 1 deletions

diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 01a9fb54ef42..146a271a74e0 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -32,6 +32,7 @@
 #ifdef CONFIG_SYSFS
 static const char fmt_hex[] = "%#x\n";
 static const char fmt_dec[] = "%d\n";
+static const char fmt_uint[] = "%u\n";
 static const char fmt_ulong[] = "%lu\n";
 static const char fmt_u64[] = "%llu\n";
 
@@ -425,6 +426,9 @@ NETDEVICE_SHOW_RW(gro_flush_timeout, fmt_ulong);
 
 static int change_napi_defer_hard_irqs(struct net_device *dev, unsigned long val)
 {
+	if (val > S32_MAX)
+		return -ERANGE;
+
 	WRITE_ONCE(dev->napi_defer_hard_irqs, val);
 	return 0;
 }
@@ -438,7 +442,7 @@ static ssize_t napi_defer_hard_irqs_store(struct device *dev,
 
 	return netdev_store(dev, attr, buf, len, change_napi_defer_hard_irqs);
 }
-NETDEVICE_SHOW_RW(napi_defer_hard_irqs, fmt_dec);
+NETDEVICE_SHOW_RW(napi_defer_hard_irqs, fmt_uint);
 
 static ssize_t ifalias_store(struct device *dev, struct device_attribute *attr,
 			     const char *buf, size_t len)