Commit a60fd8c6dbaa for kernel

commit a60fd8c6dbaa76da4163cf225ed2b9e982540f39
Author: Deepanshu Kartikey <kartikey406@gmail.com>
Date:   Wed Aug 26 19:02:58 2026 +0530

    usb: atm: usbatm: fix invalid ci_range initialization

    syzbot reported a shift-out-of-bounds in __vcc_connect():

      UBSAN: shift-out-of-bounds in net/atm/common.c:382:32
      shift exponent -1 is negative
      CPU: 0 UID: 0 PID: 5987 Comm: syz.0.18 Not tainted syzkaller #0 PREEMPT(full)
      Hardware name: Google Compute Engine/Google Compute Engine, BIOS Google 08/05/2026
      Call Trace:
       <TASK>
       dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
       ubsan_epilogue+0xa/0x30 lib/ubsan.c:233
       __ubsan_handle_shift_out_of_bounds+0x36d/0x400 lib/ubsan.c:494
       __vcc_connect+0x14b4/0x19c0 net/atm/common.c:382
       vcc_connect+0x328/0x8f0 net/atm/common.c:498
       pvc_bind+0x272/0x380 net/atm/pvc.c:52
       __sys_bind+0x2e3/0x410 net/socket.c:1976
       __x64_sys_bind+0x7a/0x90 net/socket.c:1979
       ...

    ATM device ci_range fields (vpi_bits and vci_bits) represent the
    number of bits supported for VPI and VCI addressing on the device.
    net/atm/common.c directly uses these fields as bit shift counts:
      vpi >> dev->ci_range.vpi_bits
      vci >> dev->ci_range.vci_bits
      1 << vcc->dev->ci_range.vpi_bits
      1 << vcc->dev->ci_range.vci_bits

    usbatm_atm_init() sets ci_range.vpi_bits and ci_range.vci_bits to
    ATM_CI_MAX (-1), which is defined in <uapi/linux/atmdev.h> as a
    sentinel value for userspace ATM_SETCIRANGE requests, not a valid bit
    count. Shifting by -1 is undefined behavior and triggers UBSAN
    warnings.

    ATM UNI cell headers allow up to 8 bits for VPI (0..255) and 16 bits
    for VCI (0..65535). Initialize vpi_bits to 8 and vci_bits to 16, as
    done by solos-pci.

    Fixes: c59bba75fa50 ("[PATCH] USB ATM: new usbatm core")
    Reported-by: syzbot+6665d3db5fef15914802@syzkaller.appspotmail.com
    Closes: https://syzkaller.appspot.com/bug?extid=6665d3db5fef15914802
    Suggested-by: Eric Dumazet <edumazet@google.com>
    Link: https://lore.kernel.org/all/20260824024620.23485-1-kartikey406@gmail.com/T/ [v1]
    Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
    Link: https://patch.msgid.link/20260826133258.8306-1-kartikey406@gmail.com
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/usb/atm/usbatm.c b/drivers/usb/atm/usbatm.c
index 9600e1ec0993..7b0c791399ea 100644
--- a/drivers/usb/atm/usbatm.c
+++ b/drivers/usb/atm/usbatm.c
@@ -917,8 +917,8 @@ static int usbatm_atm_init(struct usbatm_data *instance)

 	instance->atm_dev = atm_dev;

-	atm_dev->ci_range.vpi_bits = ATM_CI_MAX;
-	atm_dev->ci_range.vci_bits = ATM_CI_MAX;
+	atm_dev->ci_range.vpi_bits = 8;
+	atm_dev->ci_range.vci_bits = 16;
 	atm_dev->signal = ATM_PHY_SIG_UNKNOWN;

 	/* temp init ATM device, set to 128kbit */