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vuln-cve/data/2026/52xxx/CVE-2026-52946.json
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{
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"cveId": "CVE-2026-52946",
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"state": "PUBLISHED",
"assignerShortName": "Linux",
"dateReserved": "2026-06-09T07:44:35.371Z",
"datePublished": "2026-06-24T16:26:04.419Z",
"dateUpdated": "2026-11-10T12:47:51.036Z"
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"value": "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 ***"
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"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
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"value": "AV:N - A remote TCP peer can reach tcp_check_urg()->sk_send_sigurg()->send_sigurg() by sending TCP packets with the URG flag to a service whose socket owner is configured as a process group. The fix explicitly identifies TCP URG packet reception as a potential remote denial-of-service vector.\nAC:L - The vulnerable condition is a lock-order deadlock, but an attacker can repeatedly send URG packets and, in a plausible forking/waiting network service, induce connection churn that exercises the other tasklist_lock paths. There is no memory-layout dependency or other hard-to-satisfy condition.\nPR:N - The network attacker does not need local privileges or authentication to send TCP URG traffic to an exposed service. The fcntl process-group ownership is target service state, not an attacker privilege requirement.\nUI:N - Exploitation does not require a user to open a file or perform an interactive action. Once the service is reachable and configured, packets alone can trigger the vulnerable path.\nS:U - The impact is within the Linux kernel and the same host security authority. It does not cross a VM, sandbox, or hardware isolation boundary.\nC:N - The bug is a lock ordering deadlock, not a memory disclosure or use-after-free. The fixed traversal is RCU-safe and does not imply an attacker read primitive.\nI:N - The vulnerability does not corrupt memory or provide a write/control-flow primitive. It only causes unsafe lock acquisition ordering during signal delivery.\nA:H - The deadlock can hang kernel execution in softirq/tasklist_lock paths and deny service to the affected system. A kernel deadlock is a high availability impact."
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