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([2405:201:682f:383f:7cfc:5106:a5b2:c99c]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-396708ba872sm959764a91.1.2026.08.26.06.33.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 26 Aug 2026 06:33:08 -0700 (PDT) From: Deepanshu Kartikey To: duncan.sands@free.fr, 3chas3@gmail.com, gregkh@linuxfoundation.org, edumazet@google.com, horms@kernel.org Cc: linux-usb@vger.kernel.org, linux-atm-general@lists.sourceforge.net, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Deepanshu Kartikey , syzbot+6665d3db5fef15914802@syzkaller.appspotmail.com Subject: [PATCH v2] usb: atm: usbatm: fix invalid ci_range initialization Date: Wed, 26 Aug 2026 19:02:58 +0530 Message-ID: <20260826133258.8306-1-kartikey406@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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: 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 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 Link: https://lore.kernel.org/all/20260824024620.23485-1-kartikey406@gmail.com/T/ [v1] Signed-off-by: Deepanshu Kartikey --- drivers/usb/atm/usbatm.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) 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 */ -- 2.43.0