{"id":"CVE-2026-74640","revision":"870fd2ed7f3d4f099f0d7448e9ee70d8","records":[{"revision":"870fd2ed7f3d4f099f0d7448e9ee70d8","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-74640","aliases":[],"title":"ALSA: FCP: fix OOB write in fcp_meter_ctl_get()","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nALSA: FCP: fix OOB write in fcp_meter_ctl_get()\n\nfcp_ioctl_set_meter_map() bounds the user-supplied Level Meter map size\nby the driver's own limit of 255\n\n\tif (map.map_size < 1 || map.map_size > 255 ||\n\t map.meter_slots < 1 || map.meter_slots > 255)\n\t\treturn -EINVAL;\n\nand passes it to fcp_add_new_ctl() as the control's channel count, where\nit is stored as elem->channels.\n\nEvery control read writes into struct snd_ctl_elem_value, whose integer\narray is declared long value[128], so the limit is 128, not 255.\nfcp_meter_ctl_get() stores one 64-bit word per channel into that array\nwith no bound of its own:\n\n\tfor (i = 0; i < elem->channels; i++) {\n\t\tint idx = private->meter_level_map[i];\n\t\tint value = idx < 0 ? 0 : le32_to_cpu(resp[idx]);\n\n\t\tucontrol->value.integer.value[i] = value;\n\t}\n\nsnd_ctl_elem_read_user() serves that object from\nmemdup_user(_control, sizeof(*control)), 1224 bytes on LP64 out of\nkmalloc-2048. offsetof(struct snd_ctl_elem_value, value) is 72, so\nelement i is written at byte 72 + 8 * i and element 144 already lands\npast the allocation. At map_size 255 the last store ends at byte 2112,\n888 bytes past the object and 64 bytes into the adjacent slab object.\nThe stored words come from the device and meter_level_map[] selects\nwhich word lands in which slot, so extent and contents are both\ncontrolled.\n\nThe core does not catch this. snd_ctl_check_elem_info() is reached only\nfrom __snd_ctl_elem_info(), which snd_ctl_elem_read() calls under\nCONFIG_SND_CTL_DEBUG; without that option snd_ctl_skip_validation() is a\ncompile-time true. __snd_ctl_add_replace() validates kcontrol->count and\nnever inspects elem->channels.\n\nInstalling an oversized map needs CAP_SYS_RAWIO, but the control outlives\nthe hwdep descriptor that created it, so the out-of-bounds stores are\nissued by any process able to read controls on /dev/snd/controlC0.\n\nKASAN on 7.2.0-rc5 (arm64), triggered by an unprivileged control read:\n\n BUG: KASAN: slab-out-of-bounds in fcp_meter_ctl_get\n Write of size 8 at addr ffff000017af04c8 by task fcp_trigger/185\n __asan_store8\n fcp_meter_ctl_get\n snd_ctl_elem_read\n snd_ctl_ioctl\n Allocated by task 185:\n memdup_user\n snd_ctl_ioctl\n The buggy address is located 0 bytes to the right of\n allocated 1224-byte region [ffff000017af0000, ffff000017af04c8)\n\nBound the map size by the ABI limit rather than by 255, and bound the\nstore loop at the sink so it cannot run past the value array whatever\nelem->channels holds.\n\nDiscovered by XBOW, triaged by Baul Lee ","state":0,"publishedAt":"2026-08-22T15:32:18.957+00:00","modifiedAt":"2026-10-16T19:06:04.418+00:00","affected":[{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n \"product\": \"Linux\",\n \"vendor\": \"Linux\",\n \"defaultStatus\": \"unaffected\",\n \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n \"programFiles\": [\n \"sound/usb/fcp.c\"\n ],\n \"versions\": [\n {\n \"version\": \"46757a3e7d50dac923888e7fbe68377736f13c70\",\n \"lessThan\": \"bb30e35c36ed00f24fa39aded811f64230a913b0\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"46757a3e7d50dac923888e7fbe68377736f13c70\",\n \"lessThan\": \"bb61dc2ae59026f76db26e1909746908bc5b6f31\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"46757a3e7d50dac923888e7fbe68377736f13c70\",\n \"lessThan\": \"620f1e52a46f604635efd0fb78138afd6a513b5d\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n }\n ]\n }"},{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n \"product\": \"Linux\",\n \"vendor\": \"Linux\",\n \"defaultStatus\": \"affected\",\n \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n \"programFiles\": [\n \"sound/usb/fcp.c\"\n ],\n \"versions\": [\n {\n \"version\": \"6.14\",\n \"status\": \"affected\"\n },\n {\n \"version\": \"0\",\n \"lessThan\": \"6.14\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.18.45\",\n \"lessThanOrEqual\": \"6.18.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"7.1.9\",\n \"lessThanOrEqual\": \"7.1.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"7.2\",\n \"lessThanOrEqual\": \"*\",\n \"status\": \"unaffected\",\n \"versionType\": \"original_commit_for_fix\"\n }\n ]\n }"}],"metrics":[{"system":"CVSS 3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","score":7.8,"severity":"HIGH"}],"references":["https://git.kernel.org/stable/c/bb30e35c36ed00f24fa39aded811f64230a913b0","https://git.kernel.org/stable/c/bb61dc2ae59026f76db26e1909746908bc5b6f31","https://git.kernel.org/stable/c/620f1e52a46f604635efd0fb78138afd6a513b5d"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-74640","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-74640","identifiers":["CVE-2026-74640"]},"retained":false,"historicalAffected":[]}],"coverage":[]}