This is a note to let you know that I've just added the patch titled

usb: mon: Fix atomicity violation in mon_bin_vma_fault

to my usb git tree which can be found at git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git in the usb-testing branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will be merged to the usb-next branch sometime soon, after it passes testing, and the merge window is open.

If you have any questions about this process, please let me know.

From 2dd23cc4d0e6aa55cf9fb3b05f2f4165b01de81c Mon Sep 17 00:00:00 2001 From: Gui-Dong Han 2045gemini@gmail.com Date: Fri, 5 Jan 2024 13:24:12 +0800 Subject: usb: mon: Fix atomicity violation in mon_bin_vma_fault

In mon_bin_vma_fault(): offset = vmf->pgoff << PAGE_SHIFT; if (offset >= rp->b_size) return VM_FAULT_SIGBUS; chunk_idx = offset / CHUNK_SIZE; pageptr = rp->b_vec[chunk_idx].pg; The code is executed without holding any lock.

In mon_bin_vma_close(): spin_lock_irqsave(&rp->b_lock, flags); rp->mmap_active--; spin_unlock_irqrestore(&rp->b_lock, flags);

In mon_bin_ioctl(): spin_lock_irqsave(&rp->b_lock, flags); if (rp->mmap_active) { ... } else { ... kfree(rp->b_vec); rp->b_vec = vec; rp->b_size = size; ... } spin_unlock_irqrestore(&rp->b_lock, flags);

Concurrent execution of mon_bin_vma_fault() with mon_bin_vma_close() and mon_bin_ioctl() could lead to atomicity violations. mon_bin_vma_fault() accesses rp->b_size and rp->b_vec without locking, risking array out-of-bounds access or use-after-free bugs due to possible modifications in mon_bin_ioctl().

This possible bug is found by an experimental static analysis tool developed by our team, BassCheck[1]. This tool analyzes the locking APIs to extract function pairs that can be concurrently executed, and then analyzes the instructions in the paired functions to identify possible concurrency bugs including data races and atomicity violations. The above possible bug is reported when our tool analyzes the source code of Linux 6.2.

To address this issue, it is proposed to add a spin lock pair in mon_bin_vma_fault() to ensure atomicity. With this patch applied, our tool never reports the possible bug, with the kernel configuration allyesconfig for x86_64. Due to the lack of associated hardware, we cannot test the patch in runtime testing, and just verify it according to the code logic.

[1] https://sites.google.com/view/basscheck/

Fixes: 19e6317d24c2 ("usb: mon: Fix a deadlock in usbmon between ...") Cc: stable@vger.kernel.org Signed-off-by: Gui-Dong Han 2045gemini@gmail.com Link: https://lore.kernel.org/r/20240105052412.9377-1-2045gemini@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/usb/mon/mon_bin.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/mon/mon_bin.c b/drivers/usb/mon/mon_bin.c index 9ca9305243fe..4e30de4db1c0 100644 --- a/drivers/usb/mon/mon_bin.c +++ b/drivers/usb/mon/mon_bin.c @@ -1250,14 +1250,19 @@ static vm_fault_t mon_bin_vma_fault(struct vm_fault *vmf) struct mon_reader_bin *rp = vmf->vma->vm_private_data; unsigned long offset, chunk_idx; struct page *pageptr; + unsigned long flags;

+ spin_lock_irqsave(&rp->b_lock, flags); offset = vmf->pgoff << PAGE_SHIFT; - if (offset >= rp->b_size) + if (offset >= rp->b_size) { + spin_unlock_irqrestore(&rp->b_lock, flags); return VM_FAULT_SIGBUS; + } chunk_idx = offset / CHUNK_SIZE; pageptr = rp->b_vec[chunk_idx].pg; get_page(pageptr); vmf->page = pageptr; + spin_unlock_irqrestore(&rp->b_lock, flags); return 0; }