{"id":"CVE-2026-74640","state":"PUBLISHED","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 <baul.lee@xbow.com>","publishedAt":"2026-08-22T15:32:18.957Z","updatedAt":"2026-10-16T19:06:04.418Z","severity":{"score":7.8,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"46757a3e7d50dac923888e7fbe68377736f13c70","status":"affected","lessThan":"bb30e35c36ed00f24fa39aded811f64230a913b0","versionType":"git"},{"version":"46757a3e7d50dac923888e7fbe68377736f13c70","status":"affected","lessThan":"bb61dc2ae59026f76db26e1909746908bc5b6f31","versionType":"git"},{"version":"46757a3e7d50dac923888e7fbe68377736f13c70","status":"affected","lessThan":"620f1e52a46f604635efd0fb78138afd6a513b5d","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["sound/usb/fcp.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.14","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.14","versionType":"semver"},{"version":"6.18.45","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.9","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["sound/usb/fcp.c"]}],"references":["https://git.kernel.org/stable/c/bb30e35c36ed00f24fa39aded811f64230a913b0","https://git.kernel.org/stable/c/bb61dc2ae59026f76db26e1909746908bc5b6f31","https://git.kernel.org/stable/c/620f1e52a46f604635efd0fb78138afd6a513b5d"],"weaknesses":[],"ingestedAt":"2026-10-29T20:12:58.252Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/74xxx/CVE-2026-74640.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-74640","state":"PUBLISHED","datePublished":"2026-08-22T15:32:18.957Z","dateUpdated":"2026-10-16T19:06:04.418Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-08-15T05:44:03.922Z"},"containers":{"cna":{"title":"ALSA: FCP: fix OOB write in fcp_meter_ctl_get()","descriptions":[{"lang":"en","value":"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 <baul.lee@xbow.com>"}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"46757a3e7d50dac923888e7fbe68377736f13c70","status":"affected","lessThan":"bb30e35c36ed00f24fa39aded811f64230a913b0","versionType":"git"},{"version":"46757a3e7d50dac923888e7fbe68377736f13c70","status":"affected","lessThan":"bb61dc2ae59026f76db26e1909746908bc5b6f31","versionType":"git"},{"version":"46757a3e7d50dac923888e7fbe68377736f13c70","status":"affected","lessThan":"620f1e52a46f604635efd0fb78138afd6a513b5d","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["sound/usb/fcp.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.14","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.14","versionType":"semver"},{"version":"6.18.45","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.9","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["sound/usb/fcp.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/bb30e35c36ed00f24fa39aded811f64230a913b0"},{"url":"https://git.kernel.org/stable/c/bb61dc2ae59026f76db26e1909746908bc5b6f31"},{"url":"https://git.kernel.org/stable/c/620f1e52a46f604635efd0fb78138afd6a513b5d"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","baseScore":7.8,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:L - Exploitation is triggered by a local process issuing SNDRV_CTL_IOCTL_ELEM_READ on /dev/snd/controlC0, which reaches fcp_meter_ctl_get() via snd_ctl_elem_read_user(); there is no network, Bluetooth, or remote packet path to this code.\nAC:L - After a Level Meter map with map_size above 128 is configured, each control read deterministically performs up to 888 bytes of out-of-bounds 64-bit stores past the kmalloc-2048 buffer; no races or attacker-uncontrollable timing are required.\nPR:L - KASAN reproduced the slab OOB write from an unprivileged control read; snd_ctl_open has no capability check and the Level Meter control persists after hwdep close, so any local user with /dev/snd/controlC0 access can trigger it after normal fcp-server setup.\nUI:N - The attacker directly opens /dev/snd/controlC0 and issues the elem-read ioctl themselves; no separate victim action such as opening a file or mounting a filesystem is required.\nS:U - Impact is kernel heap corruption and local privilege escalation within the host kernel; it does not cross VM, container, or IOMMU security boundaries.\nC:H - Out-of-bounds writes corrupt up to 888 bytes beyond snd_ctl_elem_value into adjacent slab objects; attacker-influenced meter_level_map selects written values, enabling heap grooming and potential arbitrary kernel memory disclosure.\nI:H - Unbounded 64-bit stores past the 128-element value array corrupt adjacent kmalloc-2048 slab data with partially attacker-controlled contents, providing a heap corruption primitive suitable for kernel code or data overwrite.\nA:H - KASAN reported slab-out-of-bounds writes during an unprivileged control read; corrupting adjacent slab objects can cause kernel oops, panic, or hang, confirming high availability impact."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-08-25T05:41:01.874Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.14","versionEndExcluding":"6.18.45"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.14","versionEndExcluding":"7.1.9"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.14","versionEndExcluding":"7.2"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2026-74640","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"total"}],"version":"2.0.3","timestamp":"2026-10-16T19:03:29.066751Z"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-16T19:06:04.418Z"}}]}}}