# CVE-2021-47363: linux: In the Linux kernel, the following vulnerability has been resolved:  nexthop: Fix division by zero while replacing a...

CVE-2021-47363 is fixed in linux on 1 platform, first by DEBIAN-CVE-2021-47363, released May 21, 2024. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2021-47363
- Priority: Routine
- CVSS: 5.5 (medium)
- EPSS: 0.0021
- 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:  nexthop: Fix division by zero while replacing a resilient group  The resilient nexthop group torture tests in fib_nexthop.sh exposed a possible division by zero while replacing a resilient group [1]. The division by zero occurs when the data path sees a resilient nexthop group with zero buckets.  The tests replace a resilient nexthop group in a loop while traffic is forwarded through it. The tests do not specify the number of buckets while performing the replacement, resulting in the kernel allocating a stub resilient table (i.e, 'struct nh_res_table') with zero buckets.  This table should never be visible to the data path, but the old nexthop group (i.e., 'oldg') might still be used by the data path when the stub table is assigned to it.  Fix this by only assigning the stub table to the old nexthop group after making sure the group is no longer used by the data path.  Tested with fib_nexthops.sh:  Tests passed: 222 Tests failed:   0  [1]  divide error: 0000 [#1] PREEMPT SMP KASAN  CPU: 0 PID: 1850 Comm: ping Not tainted 5.14.0-custom-10271-ga86eb53057fe #1107  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-4.fc34 04/01/2014  RIP: 0010:nexthop_select_path+0x2d2/0x1a80 [...]  Call Trace:   fib_select_multipath+0x79b/0x1530   fib_select_path+0x8fb/0x1c10   ip_route_output_key_hash_rcu+0x1198/0x2da0   ip_route_output_key_hash+0x190/0x340   ip_route_output_flow+0x21/0x120   raw_sendmsg+0x91d/0x2e10   inet_sendmsg+0x9e/0xe0   __sys_sendto+0x23d/0x360   __x64_sys_sendto+0xe1/0x1b0   do_syscall_64+0x35/0x80   entry_SYSCALL_64_after_hwframe+0x44/0xae

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 5.14.9-1 | [DEBIAN-CVE-2021-47363](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47363.md) | May 21, 2024 |
| Linux | linux Debian 13.5 (trixie) | 5.14.9-1 | [DEBIAN-CVE-2021-47363](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47363.md) | May 21, 2024 |
| Linux | linux Debian 14 | 5.14.9-1 | [DEBIAN-CVE-2021-47363](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47363.md) | May 21, 2024 |

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