{"cve":"CVE-2021-47069","nvd":{"published":"2024-03-01T22:15:46.857","modified":"2026-08-04T10:16:44.070","status":"Modified","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nipc/mqueue, msg, sem: avoid relying on a stack reference past its expiry\n\ndo_mq_timedreceive calls wq_sleep with a stack local address.  The\nsender (do_mq_timedsend) uses this address to later call pipelined_send.\n\nThis leads to a very hard to trigger race where a do_mq_timedreceive\ncall might return and leave do_mq_timedsend to rely on an invalid\naddress, causing the following crash:\n\n  RIP: 0010:wake_q_add_safe+0x13/0x60\n  Call Trace:\n   __x64_sys_mq_timedsend+0x2a9/0x490\n   do_syscall_64+0x80/0x680\n   entry_SYSCALL_64_after_hwframe+0x44/0xa9\n  RIP: 0033:0x7f5928e40343\n\nThe race occurs as:\n\n1. do_mq_timedreceive calls wq_sleep with the address of `struct\n   ext_wait_queue` on function stack (aliased as `ewq_addr` here) - it\n   holds a valid `struct ext_wait_queue *` as long as the stack has not\n   been overwritten.\n\n2. `ewq_addr` gets added to info->e_wait_q[RECV].list in wq_add, and\n   do_mq_timedsend receives it via wq_get_first_waiter(info, RECV) to call\n   __pipelined_op.\n\n3. Sender calls __pipelined_op::smp_store_release(&this->state,\n   STATE_READY).  Here is where the race window begins.  (`this` is\n   `ewq_addr`.)\n\n4. If the receiver wakes up now in do_mq_timedreceive::wq_sleep, it\n   will see `state == STATE_READY` and break.\n\n5. do_mq_timedreceive returns, and `ewq_addr` is no longer guaranteed\n   to be a `struct ext_wait_queue *` since it was on do_mq_timedreceive's\n   stack.  (Although the address may not get overwritten until another\n   function happens to touch it, which means it can persist around for an\n   indefinite time.)\n\n6. do_mq_timedsend::__pipelined_op() still believes `ewq_addr` is a\n   `struct ext_wait_queue *`, and uses it to find a task_struct to pass to\n   the wake_q_add_safe call.  In the lucky case where nothing has\n   overwritten `ewq_addr` yet, `ewq_addr->task` is the right task_struct.\n   In the unlucky case, __pipelined_op::wake_q_add_safe gets handed a\n   bogus address as the receiver's task_struct causing the crash.\n\ndo_mq_timedsend::__pipelined_op() should not dereference `this` after\nsetting STATE_READY, as the receiver counterpart is now free to return.\nChange __pipelined_op to call wake_q_add_safe on the receiver's\ntask_struct returned by get_task_struct, instead of dereferencing `this`\nwhich sits on the receiver's stack.\n\nAs Manfred pointed out, the race potentially also exists in\nipc/msg.c::expunge_all and ipc/sem.c::wake_up_sem_queue_prepare.  Fix\nthose in the same way.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H","score":7.0},"cwes":["CWE-672"],"references":["https://git.kernel.org/stable/c/4528c0c323085e645b8765913b4a7fd42cf49b65","https://git.kernel.org/stable/c/807fa14536b26803b858da878b643be72952a097","https://git.kernel.org/stable/c/a11ddb37bf367e6b5239b95ca759e5389bb46048","https://git.kernel.org/stable/c/4528c0c323085e645b8765913b4a7fd42cf49b65","https://git.kernel.org/stable/c/807fa14536b26803b858da878b643be72952a097"],"products":["linux:linux_kernel"],"source":"nvd","synced_at":"2026-10-19T21:46:54.846886191+00:00"},"epss":{"cve":"CVE-2021-47069","score":0.00263,"percentile":0.18143,"date":"2026-10-31"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}