{"id":"CVE-2026-80970","summary":"ALSA: FCP: do not copy out an uninitialised init response","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nALSA: FCP: do not copy out an uninitialised init response\n\nfcp_ioctl_init() allocates its response buffer with kmalloc() and copies\nthe whole buffer back to userspace:\n\n\tbuf_size = init.step0_resp_size + init.step2_resp_size;\n\n\tvoid *resp __free(kfree) =\n\t\tkmalloc(buf_size, GFP_KERNEL);\n\t...\n\tif (copy_to_user(arg-\u003eresp, resp, buf_size))\n\t\treturn -EFAULT;\n\nNothing clears the buffer, and the only writer of its leading\nstep0_resp_size bytes is the step-0 control transfer:\n\n\terr = snd_usb_ctl_msg(dev, usb_rcvctrlpipe(dev, 0),\n\t\tFCP_USB_REQ_STEP0,\n\t\tUSB_RECIP_INTERFACE | USB_TYPE_CLASS | USB_DIR_IN,\n\t\t0, private-\u003ebInterfaceNumber,\n\t\tstep0_resp, private-\u003estep0_resp_size);\n\tif (err \u003c 0)\n\t\treturn err;\n\nusb_fill_control_urb() does not set URB_SHORT_NOT_OK, so a short or\nzero-length data stage completes with status 0 and snd_usb_ctl_msg()\nreturns a small actual_length.  The only check is err \u003c 0, so a short\ntransfer is accepted as success.\n\nsnd_usb_ctl_msg() copies the full size back unconditionally:\n\n\tbuf = kmemdup(data, size, GFP_KERNEL);\n\t...\n\tmemcpy(data, buf, size);\n\nBytes the device never wrote are therefore restored into resp unchanged\nand copied to userspace.  step0_resp_size and step2_resp_size are each\nvalidated only to 1..255, so the caller also picks the slab cache, from\nkmalloc-8 up to kmalloc-512.\n\nOn 7.2.0-rc5 (arm64), device answering step 0 with a zero-length data\nstage, s0 = s2 = 255:\n\n  # init_on_alloc off, no spray\n  step0 window [0,255): nonzero=94/255\n  000: 00 80 60 06 00 00 ff ff 18 00 00 00 57 01 ea 01\n  010: 08 78 22 13 00 00 ff ff a8 c4 5f 80 00 80 ff ff\n\n  # same kernel, kmalloc-512 pre-seeded with an 8-byte tag\n  step0 window [0,255): nonzero=219/255  tagbytes=232\n\n  # identical run, init_on_alloc=1\n  step0 window [0,255): nonzero=0/255  tagbytes=0\n\n  # all three runs\n  step2 window [255,510): device words matched=62/62\n\na8 c4 5f 80 00 80 ff ff is the little-endian kernel text address\nffff8000805fc4a8.  The step-2 window is unaffected, so the disclosure is\nexactly the step-0 region.\n\nZero the buffer, and require the step-0 transfer to deliver the full\nstep0_resp_size bytes so a short data stage is reported as an error.\n\nDiscovered by XBOW, triaged by Baul Lee \u003cbaul.lee@xbow.com\u003e","modified":"2026-09-13T03:47:07.756861074Z","published":"2026-09-11T19:42:33.789Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/80xxx/CVE-2026-80970.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/29ab2df278ab4f1d238cd9c1c393ee00db175cba"},{"type":"WEB","url":"https://git.kernel.org/stable/c/4335e387786479889e6db691fe06d345e52ea536"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/80xxx/CVE-2026-80970.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-80970"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"46757a3e7d50dac923888e7fbe68377736f13c70"},{"fixed":"29ab2df278ab4f1d238cd9c1c393ee00db175cba"},{"fixed":"4335e387786479889e6db691fe06d345e52ea536"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-80970.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"6.14.0"},{"fixed":"7.2.4"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-80970.json"}}],"schema_version":"1.9.0"}