6.15-stable review patch. If anyone has any objections, please let me know.
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From: Takamitsu Iwai takamitz@amazon.co.jp
[ Upstream commit ae8508b25def57982493c48694ef135973bfabe0 ]
Syzbot reported a WARNING in taprio_get_start_time().
When link speed is 470,589 or greater, q->picos_per_byte becomes too small, causing length_to_duration(q, ETH_ZLEN) to return zero.
This zero value leads to validation failures in fill_sched_entry() and parse_taprio_schedule(), allowing arbitrary values to be assigned to entry->interval and cycle_time. As a result, sched->cycle can become zero.
Since SPEED_800000 is the largest defined speed in include/uapi/linux/ethtool.h, this issue can occur in realistic scenarios.
To ensure length_to_duration() returns a non-zero value for minimum-sized Ethernet frames (ETH_ZLEN = 60), picos_per_byte must be at least 17 (60 * 17 > PSEC_PER_NSEC which is 1000).
This patch enforces a minimum value of 17 for picos_per_byte when the calculated value would be lower, and adds a warning message to inform users that scheduling accuracy may be affected at very high link speeds.
Fixes: fb66df20a720 ("net/sched: taprio: extend minimum interval restriction to entire cycle too") Reported-by: syzbot+398e1ee4ca2cac05fddb@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=398e1ee4ca2cac05fddb Signed-off-by: Takamitsu Iwai takamitz@amazon.co.jp Link: https://patch.msgid.link/20250728173149.45585-1-takamitz@amazon.co.jp Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/sched/sch_taprio.c | 21 ++++++++++++++++++--- 1 file changed, 18 insertions(+), 3 deletions(-)
diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c index 2b14c81a87e5..85d84f39e220 100644 --- a/net/sched/sch_taprio.c +++ b/net/sched/sch_taprio.c @@ -43,6 +43,11 @@ static struct static_key_false taprio_have_working_mqprio; #define TAPRIO_SUPPORTED_FLAGS \ (TCA_TAPRIO_ATTR_FLAG_TXTIME_ASSIST | TCA_TAPRIO_ATTR_FLAG_FULL_OFFLOAD) #define TAPRIO_FLAGS_INVALID U32_MAX +/* Minimum value for picos_per_byte to ensure non-zero duration + * for minimum-sized Ethernet frames (ETH_ZLEN = 60). + * 60 * 17 > PSEC_PER_NSEC (1000) + */ +#define TAPRIO_PICOS_PER_BYTE_MIN 17
struct sched_entry { /* Durations between this GCL entry and the GCL entry where the @@ -1284,7 +1289,8 @@ static void taprio_start_sched(struct Qdisc *sch, }
static void taprio_set_picos_per_byte(struct net_device *dev, - struct taprio_sched *q) + struct taprio_sched *q, + struct netlink_ext_ack *extack) { struct ethtool_link_ksettings ecmd; int speed = SPEED_10; @@ -1300,6 +1306,15 @@ static void taprio_set_picos_per_byte(struct net_device *dev,
skip: picos_per_byte = (USEC_PER_SEC * 8) / speed; + if (picos_per_byte < TAPRIO_PICOS_PER_BYTE_MIN) { + if (!extack) + pr_warn("Link speed %d is too high. Schedule may be inaccurate.\n", + speed); + NL_SET_ERR_MSG_FMT_MOD(extack, + "Link speed %d is too high. Schedule may be inaccurate.", + speed); + picos_per_byte = TAPRIO_PICOS_PER_BYTE_MIN; + }
atomic64_set(&q->picos_per_byte, picos_per_byte); netdev_dbg(dev, "taprio: set %s's picos_per_byte to: %lld, linkspeed: %d\n", @@ -1324,7 +1339,7 @@ static int taprio_dev_notifier(struct notifier_block *nb, unsigned long event, if (dev != qdisc_dev(q->root)) continue;
- taprio_set_picos_per_byte(dev, q); + taprio_set_picos_per_byte(dev, q, NULL);
stab = rtnl_dereference(q->root->stab);
@@ -1848,7 +1863,7 @@ static int taprio_change(struct Qdisc *sch, struct nlattr *opt, q->flags = taprio_flags;
/* Needed for length_to_duration() during netlink attribute parsing */ - taprio_set_picos_per_byte(dev, q); + taprio_set_picos_per_byte(dev, q, extack);
err = taprio_parse_mqprio_opt(dev, mqprio, extack, q->flags); if (err < 0)