{"dataType":"CVE_RECORD","dataVersion":"5.1","cveMetadata":{"cveId":"CVE-2021-47118","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","state":"PUBLISHED","assignerShortName":"Linux","dateReserved":"2024-03-04T18:12:48.838Z","datePublished":"2024-03-15T20:14:25.116Z","dateUpdated":"2025-05-04T07:04:30.329Z"},"containers":{"cna":{"providerMetadata":{"orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux","dateUpdated":"2025-05-04T07:04:30.329Z"},"descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\npid: take a reference when initializing `cad_pid`\n\nDuring boot, kernel_init_freeable() initializes `cad_pid` to the init\ntask's struct pid.  Later on, we may change `cad_pid` via a sysctl, and\nwhen this happens proc_do_cad_pid() will increment the refcount on the\nnew pid via get_pid(), and will decrement the refcount on the old pid\nvia put_pid().  As we never called get_pid() when we initialized\n`cad_pid`, we decrement a reference we never incremented, can therefore\nfree the init task's struct pid early.  As there can be dangling\nreferences to the struct pid, we can later encounter a use-after-free\n(e.g.  when delivering signals).\n\nThis was spotted when fuzzing v5.13-rc3 with Syzkaller, but seems to\nhave been around since the conversion of `cad_pid` to struct pid in\ncommit 9ec52099e4b8 (\"[PATCH] replace cad_pid by a struct pid\") from the\npre-KASAN stone age of v2.6.19.\n\nFix this by getting a reference to the init task's struct pid when we\nassign it to `cad_pid`.\n\nFull KASAN splat below.\n\n   ==================================================================\n   BUG: KASAN: use-after-free in ns_of_pid include/linux/pid.h:153 [inline]\n   BUG: KASAN: use-after-free in task_active_pid_ns+0xc0/0xc8 kernel/pid.c:509\n   Read of size 4 at addr ffff23794dda0004 by task syz-executor.0/273\n\n   CPU: 1 PID: 273 Comm: syz-executor.0 Not tainted 5.12.0-00001-g9aef892b2d15 #1\n   Hardware name: linux,dummy-virt (DT)\n   Call trace:\n    ns_of_pid include/linux/pid.h:153 [inline]\n    task_active_pid_ns+0xc0/0xc8 kernel/pid.c:509\n    do_notify_parent+0x308/0xe60 kernel/signal.c:1950\n    exit_notify kernel/exit.c:682 [inline]\n    do_exit+0x2334/0x2bd0 kernel/exit.c:845\n    do_group_exit+0x108/0x2c8 kernel/exit.c:922\n    get_signal+0x4e4/0x2a88 kernel/signal.c:2781\n    do_signal arch/arm64/kernel/signal.c:882 [inline]\n    do_notify_resume+0x300/0x970 arch/arm64/kernel/signal.c:936\n    work_pending+0xc/0x2dc\n\n   Allocated by task 0:\n    slab_post_alloc_hook+0x50/0x5c0 mm/slab.h:516\n    slab_alloc_node mm/slub.c:2907 [inline]\n    slab_alloc mm/slub.c:2915 [inline]\n    kmem_cache_alloc+0x1f4/0x4c0 mm/slub.c:2920\n    alloc_pid+0xdc/0xc00 kernel/pid.c:180\n    copy_process+0x2794/0x5e18 kernel/fork.c:2129\n    kernel_clone+0x194/0x13c8 kernel/fork.c:2500\n    kernel_thread+0xd4/0x110 kernel/fork.c:2552\n    rest_init+0x44/0x4a0 init/main.c:687\n    arch_call_rest_init+0x1c/0x28\n    start_kernel+0x520/0x554 init/main.c:1064\n    0x0\n\n   Freed by task 270:\n    slab_free_hook mm/slub.c:1562 [inline]\n    slab_free_freelist_hook+0x98/0x260 mm/slub.c:1600\n    slab_free mm/slub.c:3161 [inline]\n    kmem_cache_free+0x224/0x8e0 mm/slub.c:3177\n    put_pid.part.4+0xe0/0x1a8 kernel/pid.c:114\n    put_pid+0x30/0x48 kernel/pid.c:109\n    proc_do_cad_pid+0x190/0x1b0 kernel/sysctl.c:1401\n    proc_sys_call_handler+0x338/0x4b0 fs/proc/proc_sysctl.c:591\n    proc_sys_write+0x34/0x48 fs/proc/proc_sysctl.c:617\n    call_write_iter include/linux/fs.h:1977 [inline]\n    new_sync_write+0x3ac/0x510 fs/read_write.c:518\n    vfs_write fs/read_write.c:605 [inline]\n    vfs_write+0x9c4/0x1018 fs/read_write.c:585\n    ksys_write+0x124/0x240 fs/read_write.c:658\n    __do_sys_write fs/read_write.c:670 [inline]\n    __se_sys_write fs/read_write.c:667 [inline]\n    __arm64_sys_write+0x78/0xb0 fs/read_write.c:667\n    __invoke_syscall arch/arm64/kernel/syscall.c:37 [inline]\n    invoke_syscall arch/arm64/kernel/syscall.c:49 [inline]\n    el0_svc_common.constprop.1+0x16c/0x388 arch/arm64/kernel/syscall.c:129\n    do_el0_svc+0xf8/0x150 arch/arm64/kernel/syscall.c:168\n    el0_svc+0x28/0x38 arch/arm64/kernel/entry-common.c:416\n    el0_sync_handler+0x134/0x180 arch/arm64/kernel/entry-common.c:432\n    el0_sync+0x154/0x180 arch/arm64/kernel/entry.S:701\n\n   The buggy address belongs to the object at ffff23794dda0000\n    which belongs to the cache pid of size 224\n   The buggy address is located 4 bytes inside of\n    224-byte region [ff\n---truncated---"}],"affected":[{"product":"Linux","vendor":"Linux","defaultStatus":"unaffected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["init/main.c"],"versions":[{"version":"9ec52099e4b8678a60e9f93e41ad87885d64f3e6","lessThan":"764c2e892d1fe895392aff62fb353fdce43bb529","status":"affected","versionType":"git"},{"version":"9ec52099e4b8678a60e9f93e41ad87885d64f3e6","lessThan":"f86c80515a8a3703e0ca2e56deb50fc2879c5ea4","status":"affected","versionType":"git"},{"version":"9ec52099e4b8678a60e9f93e41ad87885d64f3e6","lessThan":"4dbd8808a591b49b717862e6e0081bcf14a87788","status":"affected","versionType":"git"},{"version":"9ec52099e4b8678a60e9f93e41ad87885d64f3e6","lessThan":"d106f05432e60f9f62d456ef017687f5c73cb414","status":"affected","versionType":"git"},{"version":"9ec52099e4b8678a60e9f93e41ad87885d64f3e6","lessThan":"2cd6eedfa6344f5ef5c3dac3aee57a39b5b46dff","status":"affected","versionType":"git"},{"version":"9ec52099e4b8678a60e9f93e41ad87885d64f3e6","lessThan":"7178be006d495ffb741c329012da289b62dddfe6","status":"affected","versionType":"git"},{"version":"9ec52099e4b8678a60e9f93e41ad87885d64f3e6","lessThan":"b8ff869f20152fbe66b6c2e2715d26a2f9897cca","status":"affected","versionType":"git"},{"version":"9ec52099e4b8678a60e9f93e41ad87885d64f3e6","lessThan":"0711f0d7050b9e07c44bc159bbc64ac0a1022c7f","status":"affected","versionType":"git"}]},{"product":"Linux","vendor":"Linux","defaultStatus":"affected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["init/main.c"],"versions":[{"version":"2.6.19","status":"affected"},{"version":"0","lessThan":"2.6.19","status":"unaffected","versionType":"semver"},{"version":"4.4.272","lessThanOrEqual":"4.4.*","status":"unaffected","versionType":"semver"},{"version":"4.9.272","lessThanOrEqual":"4.9.*","status":"unaffected","versionType":"semver"},{"version":"4.14.236","lessThanOrEqual":"4.14.*","status":"unaffected","versionType":"semver"},{"version":"4.19.194","lessThanOrEqual":"4.19.*","status":"unaffected","versionType":"semver"},{"version":"5.4.125","lessThanOrEqual":"5.4.*","status":"unaffected","versionType":"semver"},{"version":"5.10.43","lessThanOrEqual":"5.10.*","status":"unaffected","versionType":"semver"},{"version":"5.12.10","lessThanOrEqual":"5.12.*","status":"unaffected","versionType":"semver"},{"version":"5.13","lessThanOrEqual":"*","status":"unaffected","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.19","versionEndExcluding":"4.4.272"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.19","versionEndExcluding":"4.9.272"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.19","versionEndExcluding":"4.14.236"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.19","versionEndExcluding":"4.19.194"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.19","versionEndExcluding":"5.4.125"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.19","versionEndExcluding":"5.10.43"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.19","versionEndExcluding":"5.12.10"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.19","versionEndExcluding":"5.13"}]}]}],"references":[{"url":"https://git.kernel.org/stable/c/764c2e892d1fe895392aff62fb353fdce43bb529"},{"url":"https://git.kernel.org/stable/c/f86c80515a8a3703e0ca2e56deb50fc2879c5ea4"},{"url":"https://git.kernel.org/stable/c/4dbd8808a591b49b717862e6e0081bcf14a87788"},{"url":"https://git.kernel.org/stable/c/d106f05432e60f9f62d456ef017687f5c73cb414"},{"url":"https://git.kernel.org/stable/c/2cd6eedfa6344f5ef5c3dac3aee57a39b5b46dff"},{"url":"https://git.kernel.org/stable/c/7178be006d495ffb741c329012da289b62dddfe6"},{"url":"https://git.kernel.org/stable/c/b8ff869f20152fbe66b6c2e2715d26a2f9897cca"},{"url":"https://git.kernel.org/stable/c/0711f0d7050b9e07c44bc159bbc64ac0a1022c7f"}],"title":"pid: 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Coordinator","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"partial"}],"version":"2.0.3","timestamp":"2024-09-10T15:55:32.497500Z"}}}],"title":"CISA ADP Vulnrichment","providerMetadata":{"orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","shortName":"CISA-ADP","dateUpdated":"2024-09-11T17:33:25.590Z"}}]}}