CVE-2021-47118 Affecting kernel-rt-debug-core package, versions <0:4.18.0-553.5.1.rt7.346.el8_10
Threat Intelligence
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- published5 Jun 2024
- disclosed5 Jun 2024
Introduced: 5 Jun 2024
CVE-2021-47118 (opens in a new tab)How to fix?
Upgrade AlmaLinux:8 kernel-rt-debug-core to version 0:4.18.0-553.5.1.rt7.346.el8_10 or higher.
This issue was patched in ALSA-2024:3627.
NVD Description
Note: Versions mentioned in the description apply only to the upstream kernel-rt-debug-core package and not the kernel-rt-debug-core package as distributed by AlmaLinux.
See How to fix? for AlmaLinux:8 relevant fixed versions and status.
In the Linux kernel, the following vulnerability has been resolved:
pid: take a reference when initializing cad_pid
During boot, kernel_init_freeable() initializes cad_pid to the init
task's struct pid. Later on, we may change cad_pid via a sysctl, and
when this happens proc_do_cad_pid() will increment the refcount on the
new pid via get_pid(), and will decrement the refcount on the old pid
via put_pid(). As we never called get_pid() when we initialized
cad_pid, we decrement a reference we never incremented, can therefore
free the init task's struct pid early. As there can be dangling
references to the struct pid, we can later encounter a use-after-free
(e.g. when delivering signals).
This was spotted when fuzzing v5.13-rc3 with Syzkaller, but seems to
have been around since the conversion of cad_pid to struct pid in
commit 9ec52099e4b8 ("[PATCH] replace cad_pid by a struct pid") from the
pre-KASAN stone age of v2.6.19.
Fix this by getting a reference to the init task's struct pid when we
assign it to cad_pid.
Full KASAN splat below.
================================================================== BUG: KASAN: use-after-free in ns_of_pid include/linux/pid.h:153 [inline] BUG: KASAN: use-after-free in task_active_pid_ns+0xc0/0xc8 kernel/pid.c:509 Read of size 4 at addr ffff23794dda0004 by task syz-executor.0/273
CPU: 1 PID: 273 Comm: syz-executor.0 Not tainted 5.12.0-00001-g9aef892b2d15 #1 Hardware name: linux,dummy-virt (DT) Call trace: ns_of_pid include/linux/pid.h:153 [inline] task_active_pid_ns+0xc0/0xc8 kernel/pid.c:509 do_notify_parent+0x308/0xe60 kernel/signal.c:1950 exit_notify kernel/exit.c:682 [inline] do_exit+0x2334/0x2bd0 kernel/exit.c:845 do_group_exit+0x108/0x2c8 kernel/exit.c:922 get_signal+0x4e4/0x2a88 kernel/signal.c:2781 do_signal arch/arm64/kernel/signal.c:882 [inline] do_notify_resume+0x300/0x970 arch/arm64/kernel/signal.c:936 work_pending+0xc/0x2dc
Allocated by task 0: slab_post_alloc_hook+0x50/0x5c0 mm/slab.h:516 slab_alloc_node mm/slub.c:2907 [inline] slab_alloc mm/slub.c:2915 [inline] kmem_cache_alloc+0x1f4/0x4c0 mm/slub.c:2920 alloc_pid+0xdc/0xc00 kernel/pid.c:180 copy_process+0x2794/0x5e18 kernel/fork.c:2129 kernel_clone+0x194/0x13c8 kernel/fork.c:2500 kernel_thread+0xd4/0x110 kernel/fork.c:2552 rest_init+0x44/0x4a0 init/main.c:687 arch_call_rest_init+0x1c/0x28 start_kernel+0x520/0x554 init/main.c:1064 0x0
Freed by task 270: slab_free_hook mm/slub.c:1562 [inline] slab_free_freelist_hook+0x98/0x260 mm/slub.c:1600 slab_free mm/slub.c:3161 [inline] kmem_cache_free+0x224/0x8e0 mm/slub.c:3177 put_pid.part.4+0xe0/0x1a8 kernel/pid.c:114 put_pid+0x30/0x48 kernel/pid.c:109 proc_do_cad_pid+0x190/0x1b0 kernel/sysctl.c:1401 proc_sys_call_handler+0x338/0x4b0 fs/proc/proc_sysctl.c:591 proc_sys_write+0x34/0x48 fs/proc/proc_sysctl.c:617 call_write_iter include/linux/fs.h:1977 [inline] new_sync_write+0x3ac/0x510 fs/read_write.c:518 vfs_write fs/read_write.c:605 [inline] vfs_write+0x9c4/0x1018 fs/read_write.c:585 ksys_write+0x124/0x240 fs/read_write.c:658 __do_sys_write fs/read_write.c:670 [inline] __se_sys_write fs/read_write.c:667 [inline] __arm64_sys_write+0x78/0xb0 fs/read_write.c:667 __invoke_syscall arch/arm64/kernel/syscall.c:37 [inline] invoke_syscall arch/arm64/kernel/syscall.c:49 [inline] el0_svc_common.constprop.1+0x16c/0x388 arch/arm64/kernel/syscall.c:129 do_el0_svc+0xf8/0x150 arch/arm64/kernel/syscall.c:168 el0_svc+0x28/0x38 arch/arm64/kernel/entry-common.c:416 el0_sync_handler+0x134/0x180 arch/arm64/kernel/entry-common.c:432 el0_sync+0x154/0x180 arch/arm64/kernel/entry.S:701
The buggy address belongs to the object at ffff23794dda0000 which belongs to the cache pid of size 224 The buggy address is located 4 bytes inside of 224-byte region [ff ---truncated---
References
- https://errata.almalinux.org/8/ALSA-2024-3618.html
- https://errata.almalinux.org/8/ALSA-2024-3627.html
- https://access.redhat.com/security/cve/CVE-2021-47118
- https://access.redhat.com/errata/RHSA-2024:3618
- https://access.redhat.com/errata/RHSA-2024:3627
- https://git.kernel.org/stable/c/0711f0d7050b9e07c44bc159bbc64ac0a1022c7f
- https://git.kernel.org/stable/c/2cd6eedfa6344f5ef5c3dac3aee57a39b5b46dff
- https://git.kernel.org/stable/c/4dbd8808a591b49b717862e6e0081bcf14a87788
- https://git.kernel.org/stable/c/7178be006d495ffb741c329012da289b62dddfe6
- https://git.kernel.org/stable/c/764c2e892d1fe895392aff62fb353fdce43bb529
- https://git.kernel.org/stable/c/b8ff869f20152fbe66b6c2e2715d26a2f9897cca
- https://git.kernel.org/stable/c/d106f05432e60f9f62d456ef017687f5c73cb414
- https://git.kernel.org/stable/c/f86c80515a8a3703e0ca2e56deb50fc2879c5ea4