From: Alan Stern <stern@rowland.harvard.edu> stable inclusion from stable-v5.10.96 commit e3b131e30e612ff0e32de6c1cb4f69f89db29193 category: bugfix bugzilla: https://gitee.com/src-openeuler/kernel/issues/IA72HV CVE: CVE-2022-48760 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- commit 26fbe9772b8c459687930511444ce443011f86bf upstream. The syzbot fuzzer has identified a bug in which processes hang waiting for usb_kill_urb() to return. It turns out the issue is not unlinking the URB; that works just fine. Rather, the problem arises when the wakeup notification that the URB has completed is not received. The reason is memory-access ordering on SMP systems. In outline form, usb_kill_urb() and __usb_hcd_giveback_urb() operating concurrently on different CPUs perform the following actions: CPU 0 CPU 1 ---------------------------- --------------------------------- usb_kill_urb(): __usb_hcd_giveback_urb(): ... ... atomic_inc(&urb->reject); atomic_dec(&urb->use_count); ... ... wait_event(usb_kill_urb_queue, atomic_read(&urb->use_count) == 0); if (atomic_read(&urb->reject)) wake_up(&usb_kill_urb_queue); Confining your attention to urb->reject and urb->use_count, you can see that the overall pattern of accesses on CPU 0 is: write urb->reject, then read urb->use_count; whereas the overall pattern of accesses on CPU 1 is: write urb->use_count, then read urb->reject. This pattern is referred to in memory-model circles as SB (for "Store Buffering"), and it is well known that without suitable enforcement of the desired order of accesses -- in the form of memory barriers -- it is entirely possible for one or both CPUs to execute their reads ahead of their writes. The end result will be that sometimes CPU 0 sees the old un-decremented value of urb->use_count while CPU 1 sees the old un-incremented value of urb->reject. Consequently CPU 0 ends up on the wait queue and never gets woken up, leading to the observed hang in usb_kill_urb(). The same pattern of accesses occurs in usb_poison_urb() and the failure pathway of usb_hcd_submit_urb(). The problem is fixed by adding suitable memory barriers. To provide proper memory-access ordering in the SB pattern, a full barrier is required on both CPUs. The atomic_inc() and atomic_dec() accesses themselves don't provide any memory ordering, but since they are present, we can use the optimized smp_mb__after_atomic() memory barrier in the various routines to obtain the desired effect. This patch adds the necessary memory barriers. CC: <stable@vger.kernel.org> Reported-and-tested-by: syzbot+76629376e06e2c2ad626@syzkaller.appspotmail.com Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Link: https://lore.kernel.org/r/Ye8K0QYee0Q0Nna2@rowland.harvard.edu Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Cheng Yu <serein.chengyu@huawei.com> --- drivers/usb/core/hcd.c | 14 ++++++++++++++ drivers/usb/core/urb.c | 12 ++++++++++++ 2 files changed, 26 insertions(+) diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c index 62e6c526e6ed..acff95a9f239 100644 --- a/drivers/usb/core/hcd.c +++ b/drivers/usb/core/hcd.c @@ -1663,6 +1663,13 @@ int usb_hcd_submit_urb (struct urb *urb, gfp_t mem_flags) urb->hcpriv = NULL; INIT_LIST_HEAD(&urb->urb_list); atomic_dec(&urb->use_count); + /* + * Order the write of urb->use_count above before the read + * of urb->reject below. Pairs with the memory barriers in + * usb_kill_urb() and usb_poison_urb(). + */ + smp_mb__after_atomic(); + atomic_dec(&urb->dev->urbnum); if (atomic_read(&urb->reject)) wake_up(&usb_kill_urb_queue); @@ -1772,6 +1779,13 @@ static void __usb_hcd_giveback_urb(struct urb *urb) usb_anchor_resume_wakeups(anchor); atomic_dec(&urb->use_count); + /* + * Order the write of urb->use_count above before the read + * of urb->reject below. Pairs with the memory barriers in + * usb_kill_urb() and usb_poison_urb(). + */ + smp_mb__after_atomic(); + if (unlikely(atomic_read(&urb->reject))) wake_up(&usb_kill_urb_queue); usb_put_urb(urb); diff --git a/drivers/usb/core/urb.c b/drivers/usb/core/urb.c index 5e844097a9e3..abf4681159df 100644 --- a/drivers/usb/core/urb.c +++ b/drivers/usb/core/urb.c @@ -692,6 +692,12 @@ void usb_kill_urb(struct urb *urb) if (!(urb && urb->dev && urb->ep)) return; atomic_inc(&urb->reject); + /* + * Order the write of urb->reject above before the read + * of urb->use_count below. Pairs with the barriers in + * __usb_hcd_giveback_urb() and usb_hcd_submit_urb(). + */ + smp_mb__after_atomic(); usb_hcd_unlink_urb(urb, -ENOENT); wait_event(usb_kill_urb_queue, atomic_read(&urb->use_count) == 0); @@ -733,6 +739,12 @@ void usb_poison_urb(struct urb *urb) if (!urb) return; atomic_inc(&urb->reject); + /* + * Order the write of urb->reject above before the read + * of urb->use_count below. Pairs with the barriers in + * __usb_hcd_giveback_urb() and usb_hcd_submit_urb(). + */ + smp_mb__after_atomic(); if (!urb->dev || !urb->ep) return; -- 2.25.1