[PATCH v2] usb: storage: sierra_ms: reject short SWoC info transfers

sierra_get_swoc_info() requests sizeof(struct swoc_info) (60) bytes
from the device via usb_control_msg(), but its callers only treat a
negative return value as failure. A device that answers the
vendor-specific GetSwocInfo request with a short IN transfer is
therefore accepted, leaving the tail of the freshly allocated
(kmalloc(), non-zeroing) swoc_info buffer uninitialized.

truinst_show() subsequently prints swocInfo->rev, swocInfo->LinuxSKU
and swocInfo->LinuxVer from that buffer into the world-readable
(0444) "truinst" sysfs attribute. An emulated/malicious USB device
(VID 0x1199, PID 0x0fff) can exploit this to disclose up to 5 bytes
of stale kernel heap memory (kmalloc-64) to unprivileged userspace,
once per sysfs read, indefinitely. On kernels built without
init_on_alloc this leaks recently freed heap contents.

Only accept the transfer when the full structure was received.
sierra_ms_init() already retries failed queries, so well-behaved
devices are unaffected.

Fixes: 32fe5e393455 ("USB Storage Sierra: TRU-Install feature update")
Cc: stable@vger.kernel.org
Signed-off-by: Syed Labeeq Sajid Bukhari <redacted>
Assisted-by: Kimi:K2 [Kimi Code CLI]
---
v2: add blank line before the comment block; add Assisted-by tag.
    No functional change.
 drivers/usb/storage/sierra_ms.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/usb/storage/sierra_ms.c b/drivers/usb/storage/sierra_ms.c
index 177fa6cd143ab2837640c26f8336781ddd3cf9cb..d8fe9561b2b5f4cce6aa8702309cfc195bc3c891 100644
--- a/drivers/usb/storage/sierra_ms.c
+++ b/drivers/usb/storage/sierra_ms.c

@@ -77,6 +77,13 @@
 			sizeof(struct swoc_info),	/* __u16 size 	     */
 			USB_CTRL_SET_TIMEOUT);		/* int timeout 	     */
 
+	/*
+	 * A short IN transfer leaves the tail of swocInfo uninitialized;
+	 * only a full transfer is valid.
+	 */
+	if (result != sizeof(struct swoc_info))
+		return -EIO;
+
 	swocInfo->LinuxSKU = le16_to_cpu(swocInfo->LinuxSKU);
 	swocInfo->LinuxVer = le16_to_cpu(swocInfo->LinuxVer);
 	return result;

-- 
2.43.0