# CVE-2021-47418: linux: In the Linux kernel, the following vulnerability has been resolved:  net_sched: fix NULL deref in fifo_set_limit()  s...

CVE-2021-47418 is fixed in linux on 1 platform, first by DEBIAN-CVE-2021-47418, released May 21, 2024. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2021-47418
- Priority: Routine
- CVSS: 5.5 (medium)
- EPSS: 0.0023
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: May 21, 2024

## Description

In the Linux kernel, the following vulnerability has been resolved:  net_sched: fix NULL deref in fifo_set_limit()  syzbot reported another NULL deref in fifo_set_limit() [1]  I could repro the issue with :  unshare -n tc qd add dev lo root handle 1:0 tbf limit 200000 burst 70000 rate 100Mbit tc qd replace dev lo parent 1:0 pfifo_fast tc qd change dev lo root handle 1:0 tbf limit 300000 burst 70000 rate 100Mbit  pfifo_fast does not have a change() operation. Make fifo_set_limit() more robust about this.  [1] BUG: kernel NULL pointer dereference, address: 0000000000000000 PGD 1cf99067 P4D 1cf99067 PUD 7ca49067 PMD 0 Oops: 0010 [#1] PREEMPT SMP KASAN CPU: 1 PID: 14443 Comm: syz-executor959 Not tainted 5.15.0-rc3-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 RIP: 0010:0x0 Code: Unable to access opcode bytes at RIP 0xffffffffffffffd6. RSP: 0018:ffffc9000e2f7310 EFLAGS: 00010246 RAX: dffffc0000000000 RBX: ffffffff8d6ecc00 RCX: 0000000000000000 RDX: 0000000000000000 RSI: ffff888024c27910 RDI: ffff888071e34000 RBP: ffff888071e34000 R08: 0000000000000001 R09: ffffffff8fcfb947 R10: 0000000000000001 R11: 0000000000000000 R12: ffff888024c27910 R13: ffff888071e34018 R14: 0000000000000000 R15: ffff88801ef74800 FS:  00007f321d897700(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: ffffffffffffffd6 CR3: 00000000722c3000 CR4: 00000000003506e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace:  fifo_set_limit net/sched/sch_fifo.c:242 [inline]  fifo_set_limit+0x198/0x210 net/sched/sch_fifo.c:227  tbf_change+0x6ec/0x16d0 net/sched/sch_tbf.c:418  qdisc_change net/sched/sch_api.c:1332 [inline]  tc_modify_qdisc+0xd9a/0x1a60 net/sched/sch_api.c:1634  rtnetlink_rcv_msg+0x413/0xb80 net/core/rtnetlink.c:5572  netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2504  netlink_unicast_kernel net/netlink/af_netlink.c:1314 [inline]  netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1340  netlink_sendmsg+0x86d/0xdb0 net/netlink/af_netlink.c:1929  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

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 5.14.12-1 | [DEBIAN-CVE-2021-47418](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47418.md) | May 21, 2024 |
| Linux | linux Debian 13.5 (trixie) | 5.14.12-1 | [DEBIAN-CVE-2021-47418](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47418.md) | May 21, 2024 |
| Linux | linux Debian 14 | 5.14.12-1 | [DEBIAN-CVE-2021-47418](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47418.md) | May 21, 2024 |

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