| Message ID | tencent_5E4FB78DACA5F90D97926A5DBE5D96993007@qq.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [V2] USB: usbtmc: prevent kernel-usb-infoleak | expand |
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@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=9d34f80f841e948c3fdb > Signed-off-by: Edward Adam Davis <eadavis@qq.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
On Fri, 6 Sep 2024 10:28:11 -0400, Alan Stern wrote: > 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? I just found out that the logic of aligned calculation is like this. As for why it is calculated like this, perhaps Guido Kiener can provide a clearer explanation. It was introduced by commit 4d5e18d9ed93 ("usb: usbtmc: Optimize usbtmc_write"). > > > 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@syzkaller.appspotmail.com > > Closes: https://syzkaller.appspot.com/bug?extid=9d34f80f841e948c3fdb > > Signed-off-by: Edward Adam Davis <eadavis@qq.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) Logically, it seems possible to write it this way. > > ? > > 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); BR, Edward
On Sat, Sep 07, 2024 at 10:08:57AM +0800, Edward Adam Davis wrote: > On Fri, 6 Sep 2024 10:28:11 -0400, Alan Stern wrote: > > 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? > I just found out that the logic of aligned calculation is like this. > As for why it is calculated like this, perhaps Guido Kiener can provide > a clearer explanation. > It was introduced by commit 4d5e18d9ed93 ("usb: usbtmc: Optimize usbtmc_write"). > > > > > 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@syzkaller.appspotmail.com > > > Closes: https://syzkaller.appspot.com/bug?extid=9d34f80f841e948c3fdb > > > Signed-off-by: Edward Adam Davis <eadavis@qq.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) > Logically, it seems possible to write it this way. In fact, what you wrote is wrong. Consider the case where buflen is 32 and transfersize is 17. Then aligned = (12 + 17 + 3) & ~3 = 32, so your condition would fail to initialize the extra 3 bytes. Alan Stern
On Sat, 7 Sep 2024 10:45:52 -0400, Alan Stern wrote: > On Sat, Sep 07, 2024 at 10:08:57AM +0800, Edward Adam Davis wrote: > > On Fri, 6 Sep 2024 10:28:11 -0400, Alan Stern wrote: > > > 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? > > I just found out that the logic of aligned calculation is like this. > > As for why it is calculated like this, perhaps Guido Kiener can provide > > a clearer explanation. > > It was introduced by commit 4d5e18d9ed93 ("usb: usbtmc: Optimize usbtmc_write"). > > > > > > > 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@syzkaller.appspotmail.com > > > > Closes: https://syzkaller.appspot.com/bug?extid=9d34f80f841e948c3fdb > > > > Signed-off-by: Edward Adam Davis <eadavis@qq.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) > > Logically, it seems possible to write it this way. > > In fact, what you wrote is wrong. Consider the case where buflen is 32 > and transfersize is 17. Then aligned = (12 + 17 + 3) & ~3 = 32, so your > condition would fail to initialize the extra 3 bytes. The buflen is equal to USBTMC_BUFSIZE and can not equal to any other value. You can find it in usbtmc_create_urb() and usbtmc_write(). Note: #define USBTMC_BUFSIZE (4096) BR, Edward
On Sun, Sep 08, 2024 at 08:59:48AM +0800, Edward Adam Davis wrote: > On Sat, 7 Sep 2024 10:45:52 -0400, Alan Stern wrote: > > On Sat, Sep 07, 2024 at 10:08:57AM +0800, Edward Adam Davis wrote: > > > On Fri, 6 Sep 2024 10:28:11 -0400, Alan Stern wrote: > > > > 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? > > > I just found out that the logic of aligned calculation is like this. > > > As for why it is calculated like this, perhaps Guido Kiener can provide > > > a clearer explanation. > > > It was introduced by commit 4d5e18d9ed93 ("usb: usbtmc: Optimize usbtmc_write"). > > > > > > > > > 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@syzkaller.appspotmail.com > > > > > Closes: https://syzkaller.appspot.com/bug?extid=9d34f80f841e948c3fdb > > > > > Signed-off-by: Edward Adam Davis <eadavis@qq.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) > > > Logically, it seems possible to write it this way. > > > > In fact, what you wrote is wrong. Consider the case where buflen is 32 > > and transfersize is 17. Then aligned = (12 + 17 + 3) & ~3 = 32, so your > > condition would fail to initialize the extra 3 bytes. > The buflen is equal to USBTMC_BUFSIZE and can not equal to any other value. > You can find it in usbtmc_create_urb() and usbtmc_write(). > > Note: #define USBTMC_BUFSIZE (4096) All right, so what happens if transfersize is 4081? Then aligned will be equal to 4096, so your condition would fail to initialize the extra 3 bytes. Alan Stern
On Sat, 7 Sep 2024 21:32:28 -0400, Alan Stern wrote: > On Sun, Sep 08, 2024 at 08:59:48AM +0800, Edward Adam Davis wrote: > > On Sat, 7 Sep 2024 10:45:52 -0400, Alan Stern wrote: > > > On Sat, Sep 07, 2024 at 10:08:57AM +0800, Edward Adam Davis wrote: > > > > On Fri, 6 Sep 2024 10:28:11 -0400, Alan Stern wrote: > > > > > 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? > > > > I just found out that the logic of aligned calculation is like this. > > > > As for why it is calculated like this, perhaps Guido Kiener can provide > > > > a clearer explanation. > > > > It was introduced by commit 4d5e18d9ed93 ("usb: usbtmc: Optimize usbtmc_write"). > > > > > > > > > > > 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@syzkaller.appspotmail.com > > > > > > Closes: https://syzkaller.appspot.com/bug?extid=9d34f80f841e948c3fdb > > > > > > Signed-off-by: Edward Adam Davis <eadavis@qq.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) > > > > Logically, it seems possible to write it this way. > > > > > > In fact, what you wrote is wrong. Consider the case where buflen is 32 > > > and transfersize is 17. Then aligned = (12 + 17 + 3) & ~3 = 32, so your > > > condition would fail to initialize the extra 3 bytes. > > The buflen is equal to USBTMC_BUFSIZE and can not equal to any other value. > > You can find it in usbtmc_create_urb() and usbtmc_write(). > > > > Note: #define USBTMC_BUFSIZE (4096) > > All right, so what happens if transfersize is 4081? Then aligned will > be equal to 4096, so your condition would fail to initialize the extra 3 > bytes. Not bad, when the transfersize values are 4081, 4082, and 4083, the aligned value is 4096, which will result in 1, 2, and 3 bytes not being initialized, respectively. I will update my patch. BR, Edward
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)) + 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);
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 ... 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@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=9d34f80f841e948c3fdb Signed-off-by: Edward Adam Davis <eadavis@qq.com> --- drivers/usb/class/usbtmc.c | 4 ++++ 1 file changed, 4 insertions(+)