{"id":"CVE-2026-64191","summary":"i2c: stub: Reject I2C block transfers with invalid length","details":"In the Linux kernel, the following vulnerability has been resolved:\n\ni2c: stub: Reject I2C block transfers with invalid length\n\nThe I2C_SMBUS_I2C_BLOCK_DATA case in stub_xfer() uses data-\u003eblock[0]\nas the transfer length. The existing check only clamps it to avoid\noverrunning the chip-\u003ewords[256] register array, but does not validate\nit against I2C_SMBUS_BLOCK_MAX (32), which is the limit of the union\ni2c_smbus_data.block buffer (34 bytes total). The driver is a\ndevelopment/test tool (CONFIG_I2C_STUB=m, not built by default)\nthat must be loaded with a chip_addr= parameter.\n\nA local user with access to /dev/i2c-* can issue an I2C_SMBUS ioctl\nwith I2C_SMBUS_I2C_BLOCK_DATA and data-\u003eblock[0] \u003e 32, causing\nstub_xfer() to read or write past the end of the union\ni2c_smbus_data.block buffer:\n\n BUG: KASAN: stack-out-of-bounds in stub_xfer (drivers/i2c/i2c-stub.c:223)\n Read of size 1 at addr ffff88800abcfd92 by task exploit/81\n Call Trace:\n  \u003cTASK\u003e\n  stub_xfer (drivers/i2c/i2c-stub.c:223)\n  __i2c_smbus_xfer (drivers/i2c/i2c-core-smbus.c:593)\n  i2c_smbus_xfer (drivers/i2c/i2c-core-smbus.c:536)\n  i2cdev_ioctl_smbus (drivers/i2c/i2c-dev.c:391)\n  i2cdev_ioctl (drivers/i2c/i2c-dev.c:478)\n  __x64_sys_ioctl (fs/ioctl.c:583)\n  do_syscall_64 (arch/x86/entry/syscall_64.c:94)\n  entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)\n  \u003c/TASK\u003e\n\nThe bug exists because i2c-stub implements .smbus_xfer directly,\nbypassing the I2C_SMBUS_BLOCK_MAX validation in\ni2c_smbus_xfer_emulated(). The I2C_SMBUS_BLOCK_DATA case in the same\nfunction correctly validates against I2C_SMBUS_BLOCK_MAX, but the\nI2C_SMBUS_I2C_BLOCK_DATA case does not.\n\nFix by rejecting transfers with data-\u003eblock[0] == 0 or\ndata-\u003eblock[0] \u003e I2C_SMBUS_BLOCK_MAX with -EINVAL, consistent with\nboth the I2C_SMBUS_BLOCK_DATA case in the same function and the\nI2C_SMBUS_I2C_BLOCK_DATA validation in i2c_smbus_xfer_emulated().","modified":"2026-07-22T05:33:07.273707942Z","published":"2026-07-20T16:27:51.120Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/64xxx/CVE-2026-64191.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/0526931b16e5a118d367b7bfce7d797e63f7ac69"},{"type":"WEB","url":"https://git.kernel.org/stable/c/1c4ffe6b4f04365485ed58d64c9bb86b46fc9037"},{"type":"WEB","url":"https://git.kernel.org/stable/c/21e87f336ac6303fed54a69b1d0d79a23b25c8d0"},{"type":"WEB","url":"https://git.kernel.org/stable/c/3fd225f3e4cd67ec8ddab1afed9da03c7c43537c"},{"type":"WEB","url":"https://git.kernel.org/stable/c/4bd8635f28c135a08aac6badcd7d9b5cdb34335f"},{"type":"WEB","url":"https://git.kernel.org/stable/c/5f4d2bd028ebb6e4c09a9d64842546022321d4a7"},{"type":"WEB","url":"https://git.kernel.org/stable/c/6036b5067a8199ba7a2dc7b377d4b9dd276d5f9e"},{"type":"WEB","url":"https://git.kernel.org/stable/c/7e9072dbd5f2f17934751873450d2c22080ead80"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/64xxx/CVE-2026-64191.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-64191"},{"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":"4710317891e4824ce1510a6b5066abbd3e917750"},{"fixed":"7e9072dbd5f2f17934751873450d2c22080ead80"},{"fixed":"21e87f336ac6303fed54a69b1d0d79a23b25c8d0"},{"fixed":"3fd225f3e4cd67ec8ddab1afed9da03c7c43537c"},{"fixed":"1c4ffe6b4f04365485ed58d64c9bb86b46fc9037"},{"fixed":"4bd8635f28c135a08aac6badcd7d9b5cdb34335f"},{"fixed":"5f4d2bd028ebb6e4c09a9d64842546022321d4a7"},{"fixed":"0526931b16e5a118d367b7bfce7d797e63f7ac69"},{"fixed":"6036b5067a8199ba7a2dc7b377d4b9dd276d5f9e"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-64191.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"2.6.33"},{"fixed":"5.10.260"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.11.0"},{"fixed":"5.15.211"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.16.0"},{"fixed":"6.1.177"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.144"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.95"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.37"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.0.14"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-64191.json"}}],"schema_version":"1.7.5"}