{"id":"CVE-2026-52946","state":"PUBLISHED","title":"fs/fcntl: fix SOFTIRQ-unsafe lock order in fasync signaling","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 ***","publishedAt":"2026-06-24T16:26:04.419Z","updatedAt":"2026-10-19T19:47:09.047Z","severity":{"score":7.5,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"54626335ea4174ab2d9a183b511d825f6765e47b","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"897d6a7247739fb1528f98c575df4f2e5de7f994","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"32dbd5ce4be3a3ed7e00f8af18795cc84fc50a33","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"b5fa9e32fb6718f70c986ee14dd5d01b4846f331","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"1bee417678f1135e35b25a37734db46aa94258d2","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"20a93e397abe850c49b6fa0e8cc827b5f634a8f5","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"bfcc8e8d8a495bb34cae9e620adfb75fb13a3954","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"36c1b57b2ecf3c61ac93f5f07bd29b6f21e226ed","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"00633c4683828acd5256fa8d5163f440d74bbe71","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/fcntl.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"2.6.12","status":"affected"},{"version":"0","status":"unaffected","lessThan":"2.6.12","versionType":"semver"},{"version":"5.10.259","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.210","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.176","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.143","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.94","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.36","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.0.13","status":"unaffected","lessThanOrEqual":"7.0.*","versionType":"semver"},{"version":"7.1.1","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":["fs/fcntl.c"]}],"references":["https://git.kernel.org/stable/c/54626335ea4174ab2d9a183b511d825f6765e47b","https://git.kernel.org/stable/c/897d6a7247739fb1528f98c575df4f2e5de7f994","https://git.kernel.org/stable/c/32dbd5ce4be3a3ed7e00f8af18795cc84fc50a33","https://git.kernel.org/stable/c/b5fa9e32fb6718f70c986ee14dd5d01b4846f331","https://git.kernel.org/stable/c/1bee417678f1135e35b25a37734db46aa94258d2","https://git.kernel.org/stable/c/20a93e397abe850c49b6fa0e8cc827b5f634a8f5","https://git.kernel.org/stable/c/bfcc8e8d8a495bb34cae9e620adfb75fb13a3954","https://git.kernel.org/stable/c/36c1b57b2ecf3c61ac93f5f07bd29b6f21e226ed","https://git.kernel.org/stable/c/00633c4683828acd5256fa8d5163f440d74bbe71","https://cert-portal.siemens.com/productcert/html/ssa-019113.html","https://cert-portal.siemens.com/productcert/html/ssa-457936.html","https://cert-portal.siemens.com/productcert/html/ssa-784472.html"],"weaknesses":["CWE-362"],"ingestedAt":"2026-10-29T20:12:16.098Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/52xxx/CVE-2026-52946.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-52946","state":"PUBLISHED","datePublished":"2026-06-24T16:26:04.419Z","dateUpdated":"2026-10-19T19:47:09.047Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-06-09T07:44:35.371Z"},"containers":{"cna":{"title":"fs/fcntl: fix SOFTIRQ-unsafe lock order in fasync signaling","descriptions":[{"lang":"en","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 ***"}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"54626335ea4174ab2d9a183b511d825f6765e47b","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"897d6a7247739fb1528f98c575df4f2e5de7f994","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"32dbd5ce4be3a3ed7e00f8af18795cc84fc50a33","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"b5fa9e32fb6718f70c986ee14dd5d01b4846f331","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"1bee417678f1135e35b25a37734db46aa94258d2","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"20a93e397abe850c49b6fa0e8cc827b5f634a8f5","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"bfcc8e8d8a495bb34cae9e620adfb75fb13a3954","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"36c1b57b2ecf3c61ac93f5f07bd29b6f21e226ed","versionType":"git"},{"version":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2","status":"affected","lessThan":"00633c4683828acd5256fa8d5163f440d74bbe71","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/fcntl.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"2.6.12","status":"affected"},{"version":"0","status":"unaffected","lessThan":"2.6.12","versionType":"semver"},{"version":"5.10.259","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.210","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.176","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.143","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.94","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.36","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.0.13","status":"unaffected","lessThanOrEqual":"7.0.*","versionType":"semver"},{"version":"7.1.1","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":["fs/fcntl.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/54626335ea4174ab2d9a183b511d825f6765e47b"},{"url":"https://git.kernel.org/stable/c/897d6a7247739fb1528f98c575df4f2e5de7f994"},{"url":"https://git.kernel.org/stable/c/32dbd5ce4be3a3ed7e00f8af18795cc84fc50a33"},{"url":"https://git.kernel.org/stable/c/b5fa9e32fb6718f70c986ee14dd5d01b4846f331"},{"url":"https://git.kernel.org/stable/c/1bee417678f1135e35b25a37734db46aa94258d2"},{"url":"https://git.kernel.org/stable/c/20a93e397abe850c49b6fa0e8cc827b5f634a8f5"},{"url":"https://git.kernel.org/stable/c/bfcc8e8d8a495bb34cae9e620adfb75fb13a3954"},{"url":"https://git.kernel.org/stable/c/36c1b57b2ecf3c61ac93f5f07bd29b6f21e226ed"},{"url":"https://git.kernel.org/stable/c/00633c4683828acd5256fa8d5163f440d74bbe71"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","baseScore":7.5,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","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. 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