CVE-2021-47598 (Moderate severity, published 2024-06-18)
CVSS score: 7.8 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H)
CWE: CWE-416
Description: In the Linux kernel, the following vulnerability has been resolved:

sch_cake: do not call cake_destroy() from cake_init()

qdiscs are not supposed to call their own destroy() method
from init(), because core stack already does that.

syzbot was able to trigger use after free:

DEBUG_LOCKS_WARN_ON(lock->magic != lock)
WARNING: CPU: 0 PID: 21902 at kernel/locking/mutex.c:586 __mutex_lock_common kernel/locking/mutex.c:586 [inline]
WARNING: CPU: 0 PID: 21902 at kernel/locking/mutex.c:586 __mutex_lock+0x9ec/0x12f0 kernel/locking/mutex.c:740
Modules linked in:
CPU: 0 PID: 21902 Comm: syz-executor189 Not tainted 5.16.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:__mutex_lock_common kernel/locking/mutex.c:586 [inline]
RIP: 0010:__mutex_lock+0x9ec/0x12f0 kernel/locking/mutex.c:740
Code: 08 84 d2 0f 85 19 08 00 00 8b 05 97 38 4b 04 85 c0 0f 85 27 f7 ff ff 48 c7 c6 20 00 ac 89 48 c7 c7 a0 fe ab 89 e8 bf 76 ba ff <0f> 0b e9 0d f7 ff ff 48 8b 44 24 40 48 8d b8 c8 08 00 00 48 89 f8
RSP: 0018:ffffc9000627f290 EFLAGS: 00010282
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: ffff88802315d700 RSI: ffffffff815f1db8 RDI: fffff52000c4fe44
RBP: ffff88818f28e000 R08: 0000000000000000 R09: 0000000000000000
R10: ffffffff815ebb5e R11: 0000000000000000 R12: 0000000000000000
R13: dffffc0000000000 R14: ffffc9000627f458 R15: 0000000093c30000
FS:  0000555556abc400(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fda689c3303 CR3: 000000001cfbb000 CR4: 0000000000350ef0
Call Trace:
 <TASK>
 tcf_chain0_head_change_cb_del+0x2e/0x3d0 net/sched/cls_api.c:810
 tcf_block_put_ext net/sched/cls_api.c:1381 [inline]
 tcf_block_put_ext net/sched/cls_api.c:1376 [inline]
 tcf_block_put+0xbc/0x130 net/sched/cls_api.c:1394
 cake_destroy+0x3f/0x80 net/sched/sch_cake.c:2695
 qdisc_create.constprop.0+0x9da/0x10f0 net/sched/sch_api.c:1293
 tc_modify_qdisc+0x4c5/0x1980 net/sched/sch_api.c:1660
 rtnetlink_rcv_msg+0x413/0xb80 net/core/rtnetlink.c:5571
 netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2496
 netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
 netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1345
 netlink_sendmsg+0x904/0xdf0 net/netlink/af_netlink.c:1921
 sock_sendmsg_nosec net/socket.c:704 [inline]
 sock_sendmsg+0xcf/0x120 net/socket.c:724
 ____sys_sendmsg+0x6e8/0x810 net/socket.c:2409
 ___sys_sendmsg+0xf3/0x170 net/socket.c:2463
 __sys_sendmsg+0xe5/0x1b0 net/socket.c:2492
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7f1bb06badb9
Code: Unable to access opcode bytes at RIP 0x7f1bb06bad8f.
RSP: 002b:00007fff3012a658 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f1bb06badb9
RDX: 0000000000000000 RSI: 00000000200007c0 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000003 R09: 0000000000000003
R10: 0000000000000003 R11: 0000000000000246 R12: 00007fff3012a688
R13: 00007fff3012a6a0 R14: 00007fff3012a6e0 R15: 00000000000013c2
 </TASK>
Statement: Red Hat Enterprise Linux is not impacted by this CVE, as the vulnerability in question does not affect the specific versions or configurations of the Linux kernel used in its distributions. This ensures that users of Red Hat Enterprise Linux are not exposed to the potential risks associated with this issue, and no further action or mitigation is necessary for systems running this operating system.
Mitigation: Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.