[PATCH v2 0/2] USB: sisusbvga: Fix integer overflow and NULL dereference

[PATCH v2 0/2] USB: sisusbvga: Fix integer overflow and NULL dereference

[Vasiliy Kovalev]

This series fixes two issues in the sisusbvga driver found by static
analysis and confirmed through testing with USB gadget emulation:

1. Integer overflow in boundary check of sisusb_clear_vram() that can be
   triggered by a compromised USB device reporting inflated VRAM size.

2. NULL pointer dereference in sisusb_read_mem_bulk() when both
   kernbuffer and userbuffer are NULL, causing immediate kernel panic.

Both issues are reproducible with the 'USB Gadget Tests' framework [1].

v2:
- Patch 2/2: Move NULL check into sisusb_read_mem_bulk() and
return -EINVAL (suggested by Fedor Pchelkin)

[1] https://github.com/kovalev0/usb-gadget-tests

Vasiliy Kovalev (2):
  USB: sisusbvga: Fix integer overflow in sisusb_clear_vram
  USB: sisusbvga: Fix NULL pointer dereference in sisusb_read_mem_bulk

 drivers/usb/misc/sisusbvga/sisusbvga.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

-- 
2.50.1

[PATCH v2 1/2] USB: sisusbvga: Fix integer overflow in sisusb_clear_vram

[Vasiliy Kovalev]

The boundary check in sisusb_clear_vram():

    if (address + length > sisusb->vrambase + sisusb->vramsize)
        length = sisusb->vrambase + sisusb->vramsize - address;

is subject to unsigned 32-bit integer overflow. When address is close to
UINT32_MAX and length is non-trivial, their sum wraps around and the
guard evaluates incorrectly, allowing the check to be bypassed.

The overflow condition requires length > UINT32_MAX - address. Since
address belongs to [vrambase; vrambase + vramsize) where vrambase is
0xd0000000, and length comes from userspace via SUCMD_CLRSCR as a 24-bit
value (max 0xFFFFFF), overflow is only reachable when sisusb->vramsize
exceeds 1 GiB. A compromised USB device can return an arbitrary value for
sisusb->vramsize via SR[0x14], making this condition reachable.

Use check_add_overflow() to detect the overflow explicitly and return 1.
This ensures the driver correctly rejects invalid parameters instead of
proceeding with wrapped-around values.

Found by Linux Verification Center (linuxtesting.org) with Svace.
Tested with 'USB Gadget Tests'[1]:

$ TEST=sisusbvga-fops-svace-int-overflow
$ echo $TEST > tests/list.txt && make && sudo ./check.sh

[1] Link: https://github.com/kovalev0/usb-gadget-tests
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: <stable@vger.kernel.org>
Signed-off-by: Vasiliy Kovalev <kovalev@altlinux.org>
---
 drivers/usb/misc/sisusbvga/sisusbvga.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/misc/sisusbvga/sisusbvga.c b/drivers/usb/misc/sisusbvga/sisusbvga.c
index febf34f9f049..89d566d192aa 100644
--- a/drivers/usb/misc/sisusbvga/sisusbvga.c
+++ b/drivers/usb/misc/sisusbvga/sisusbvga.c
@@ -1301,6 +1301,7 @@ static int sisusb_clear_vram(struct sisusb_usb_data *sisusb,
 {
 	int ret, i;
 	ssize_t j;
+	u32 end_addr;
 
 	if (address < sisusb->vrambase)
 		return 1;
@@ -1308,7 +1309,10 @@ static int sisusb_clear_vram(struct sisusb_usb_data *sisusb,
 	if (address >= sisusb->vrambase + sisusb->vramsize)
 		return 1;
 
-	if (address + length > sisusb->vrambase + sisusb->vramsize)
+	if (check_add_overflow(address, (u32)length, &end_addr))
+		return 1;
+
+	if (end_addr > sisusb->vrambase + sisusb->vramsize)
 		length = sisusb->vrambase + sisusb->vramsize - address;
 
 	if (length <= 0)
-- 
2.50.1

[PATCH v2 2/2] USB: sisusbvga: Fix NULL pointer dereference in sisusb_read_mem_bulk

[Vasiliy Kovalev]

sisusb_read_mem_bulk() accepts two buffer parameters: kernbuffer for
kernel-space data and userbuffer for userspace data. The function's logic
assumes at least one of them is non-NULL:

    if (userbuffer) {
        /* userspace path */
    } else {
        /* kernel buffer path - dereferences kernbuffer */
        swap32 = *((u32 *)kernbuffer);
    }

However, when called from sisusb_read() with buffer == NULL, both
kernbuffer and userbuffer are NULL, causing immediate kernel panic:

  Oops: general protection fault, probably for non-canonical
        address 0xdffffc0000000000: 0000 [#1] SMP KASAN NOPTI
  KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
  CPU: 3 UID: 0 PID: 370 Comm: sisusbvga-fops- Not tainted 6.19.0-next-20260217 #1
  RIP: 0010:sisusb_read_mem_bulk.constprop.0 (drivers/usb/misc/sisusbvga/sisusbvga.c:1171)
  Call Trace:
   <TASK>
   __pfx_sisusb_read_mem_bulk.constprop.0 (drivers/usb/misc/sisusbvga/sisusbvga.c:1092)
   sisusb_read (drivers/usb/misc/sisusbvga/sisusbvga.c:2396)
   vfs_read (fs/read_write.c:572)
   ksys_read (fs/read_write.c:718)
   do_syscall_64 (arch/x86/entry/syscall_64.c:94)
   entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)
   RIP: 0033:0x7f335af3fefc
   </TASK>

Add parameter validation at the API level: reject the call with -EINVAL
if both buffers are NULL.

Found by Linux Verification Center (linuxtesting.org) with Svace.
Tested with 'USB Gadget Tests'[1]:

$ TEST=sisusbvga-fops-svace-null-deref
$ echo $TEST > tests/list.txt && make && sudo ./check.sh

[1] Link: https://github.com/kovalev0/usb-gadget-tests
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Suggested-by: Fedor Pchelkin <pchelkin@ispras.ru>
Cc: <stable@vger.kernel.org>
Signed-off-by: Vasiliy Kovalev <kovalev@altlinux.org>
---
v2: Move NULL check into sisusb_read_mem_bulk() and
return -EINVAL (suggested by Fedor Pchelkin)

v1: https://lore.kernel.org/all/20260218005523.1259725-3-kovalev@altlinux.org/
---
 drivers/usb/misc/sisusbvga/sisusbvga.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/usb/misc/sisusbvga/sisusbvga.c b/drivers/usb/misc/sisusbvga/sisusbvga.c
index 89d566d192aa..abda425199ee 100644
--- a/drivers/usb/misc/sisusbvga/sisusbvga.c
+++ b/drivers/usb/misc/sisusbvga/sisusbvga.c
@@ -1098,6 +1098,9 @@ static int sisusb_read_mem_bulk(struct sisusb_usb_data *sisusb, u32 addr,
 	u16 swap16;
 	u32 swap32;
 
+	if (!kernbuffer && !userbuffer)
+		return -EINVAL;
+
 	(*bytes_read = 0);
 
 	length &= 0x00ffffff;
-- 
2.50.1