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Message-ID: <25d5853a-7156-4892-a383-4547e9c95472@rowland.harvard.edu> Date: Fri, 6 Sep 2024 10:28:11 -0400 From: Alan Stern <stern@...land.harvard.edu> To: Edward Adam Davis <eadavis@...com> Cc: gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org, syzbot+9d34f80f841e948c3fdb@...kaller.appspotmail.com, syzkaller-bugs@...glegroups.com Subject: Re: [PATCH V2] USB: usbtmc: prevent kernel-usb-infoleak On Fri, Sep 06, 2024 at 10:11:03PM +0800, Edward Adam Davis wrote: > The syzbot reported a kernel-usb-infoleak in usbtmc_write. > > The expression "aligned = (transfersize + (USBTMC_HEADER_SIZE + 3)) & ~3;" > in usbtmcw_write() follows the following pattern: > > aligned = (1 + 12 + 3) & ~3 = 16 // 3 bytes have not been initialized > aligned = (2 + 12 + 3) & ~3 = 16 // 2 bytes have not been initialized > aligned = (3 + 12 + 3) & ~3 = 16 // 1 byte has not been initialized > aligned = (4 + 12 + 3) & ~3 = 16 // All bytes have been initialized > aligned = (5 + 12 + 3) & ~3 = 20 // 3 bytes have not been initialized > aligned = (6 + 12 + 3) & ~3 = 20 // 2 bytes have not been initialized > aligned = (7 + 12 + 3) & ~3 = 20 // 1 byte has not been initialized > aligned = (8 + 12 + 3) & ~3 = 20 // All bytes have been initialized > aligned = (9 + 12 + 3) & ~3 = 24 > ... What is the purpose of aligned? Why doesn't the driver simply use USBTMC_HEADER_SIZE + transfersize instead of rounding it up to a multiple of 4? > Note: #define USBTMC_HEADER_SIZE 12 > > This results in the buffer[USBTMC_SEAD_SIZE+transfersize] and its > subsequent memory not being initialized. > > The condition aligned < buflen is used to avoid out of bounds access to > the buffer[USBTMC_HEADER_SIZE + transfersize] when "transfersize = > buflen - USBTMC_HEADER_SIZE". > > Fixes: 4ddc645f40e9 ("usb: usbtmc: Add ioctl for vendor specific write") > Reported-and-tested-by: syzbot+9d34f80f841e948c3fdb@...kaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=9d34f80f841e948c3fdb > Signed-off-by: Edward Adam Davis <eadavis@...com> > --- > drivers/usb/class/usbtmc.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/drivers/usb/class/usbtmc.c b/drivers/usb/class/usbtmc.c > index 6bd9fe565385..faf8c5508997 100644 > --- a/drivers/usb/class/usbtmc.c > +++ b/drivers/usb/class/usbtmc.c > @@ -1591,6 +1591,10 @@ static ssize_t usbtmc_write(struct file *filp, const char __user *buf, > goto exit; > } > > + if (aligned < buflen && (transfersize % 4)) Shouldn't this be if (USBTMC_HEADER_SIZE + transfersize < aligned) ? Alan Stern > + memset(&buffer[USBTMC_HEADER_SIZE + transfersize], 0, > + aligned - USBTMC_HEADER_SIZE - transfersize); > + > dev_dbg(&data->intf->dev, "%s(size:%u align:%u)\n", __func__, > (unsigned int)transfersize, (unsigned int)aligned); > > -- > 2.43.0
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