{"cve":"CVE-2026-52946","nvd":{"published":"2026-06-24T17:17:04.610","modified":"2026-10-19T20:18:49.283","status":"Modified","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nfs/fcntl: fix SOFTIRQ-unsafe lock order in fasync signaling\n\nA SOFTIRQ-safe to SOFTIRQ-unsafe lock order deadlock can occur in\nsend_sigio() and send_sigurg() when a process group receives a signal.\n\nWhen FASYNC is configured for a process group (PIDTYPE_PGID), both\nfunctions use read_lock(&tasklist_lock) to traverse the task list.\nHowever, they are frequently called from softirq context:\n- send_sigio() via input_inject_event -> kill_fasync\n- send_sigurg() via tcp_check_urg -> sk_send_sigurg (NET_RX_SOFTIRQ)\n\nThe deadlock is caused by the rwlock writer fairness mechanism:\n1. CPU 0 (process context) holds read_lock(&tasklist_lock) in do_wait().\n2. CPU 1 (process context) attempts write_lock(&tasklist_lock) in\n   fork() or exit() and spins, which blocks all new readers.\n3. CPU 0 is interrupted by a softirq (e.g., TCP URG packet reception).\n4. The softirq calls send_sigurg() and attempts to acquire\n   read_lock(&tasklist_lock), deadlocking because CPU 1 is waiting.\n\nSince PID hashing and do_each_pid_task() traversals are already\nRCU-protected, the read_lock on tasklist_lock is no longer strictly\nrequired for safe traversal. Fix this by replacing tasklist_lock with\nrcu_read_lock(), aligning the process group signaling path with the\nsingle-PID path. This also mitigates a potential remote denial of\nservice vector via TCP URG packets.\n\nLockdep splat:\n=====================================================\nWARNING: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected\n[...]\nChain exists of:\n  &dev->event_lock --> &f_owner->lock --> tasklist_lock\n\nPossible interrupt unsafe locking scenario:\n       CPU0                    CPU1\n       ----                    ----\n  lock(tasklist_lock);\n                           local_irq_disable();\n                           lock(&dev->event_lock);\n                           lock(&f_owner->lock);\n  <Interrupt>\n    lock(&dev->event_lock);\n\n*** DEADLOCK ***","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","score":7.5},"cwes":["CWE-667","CWE-362"],"references":["https://git.kernel.org/stable/c/00633c4683828acd5256fa8d5163f440d74bbe71","https://git.kernel.org/stable/c/1bee417678f1135e35b25a37734db46aa94258d2","https://git.kernel.org/stable/c/20a93e397abe850c49b6fa0e8cc827b5f634a8f5","https://git.kernel.org/stable/c/32dbd5ce4be3a3ed7e00f8af18795cc84fc50a33","https://git.kernel.org/stable/c/36c1b57b2ecf3c61ac93f5f07bd29b6f21e226ed"],"products":["linux:linux_kernel"],"source":"nvd","synced_at":"2026-10-21T03:43:09.190223697+00:00"},"epss":{"cve":"CVE-2026-52946","score":0.00467,"percentile":0.40169,"date":"2026-10-25"},"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."]}