NULL Pointer Dereference Affecting bpftool package, versions <0:6.1.91-99.172.amzn2023
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Start learning- Snyk IDSNYK-AMZN2023-BPFTOOL-7445946
- published12 Jul 2024
- disclosed30 May 2024
Introduced: 30 May 2024
CVE-2024-36937 (opens in a new tab)How to fix?
Upgrade Amazon-Linux:2023 bpftool to version 0:6.1.91-99.172.amzn2023 or higher.
This issue was patched in ALAS2023-2024-643.
NVD Description
Note: Versions mentioned in the description apply only to the upstream bpftool package and not the bpftool package as distributed by Amazon-Linux.
See How to fix? for Amazon-Linux:2023 relevant fixed versions and status.
In the Linux kernel, the following vulnerability has been resolved:
xdp: use flags field to disambiguate broadcast redirect
When redirecting a packet using XDP, the bpf_redirect_map() helper will set up the redirect destination information in struct bpf_redirect_info (using the __bpf_xdp_redirect_map() helper function), and the xdp_do_redirect() function will read this information after the XDP program returns and pass the frame on to the right redirect destination.
When using the BPF_F_BROADCAST flag to do multicast redirect to a whole map, __bpf_xdp_redirect_map() sets the 'map' pointer in struct bpf_redirect_info to point to the destination map to be broadcast. And xdp_do_redirect() reacts to the value of this map pointer to decide whether it's dealing with a broadcast or a single-value redirect. However, if the destination map is being destroyed before xdp_do_redirect() is called, the map pointer will be cleared out (by bpf_clear_redirect_map()) without waiting for any XDP programs to stop running. This causes xdp_do_redirect() to think that the redirect was to a single target, but the target pointer is also NULL (since broadcast redirects don't have a single target), so this causes a crash when a NULL pointer is passed to dev_map_enqueue().
To fix this, change xdp_do_redirect() to react directly to the presence of the BPF_F_BROADCAST flag in the 'flags' value in struct bpf_redirect_info to disambiguate between a single-target and a broadcast redirect. And only read the 'map' pointer if the broadcast flag is set, aborting if that has been cleared out in the meantime. This prevents the crash, while keeping the atomic (cmpxchg-based) clearing of the map pointer itself, and without adding any more checks in the non-broadcast fast path.
References
- http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2024-36937
- https://git.kernel.org/stable/c/12481f30128fbebc2eeb55eb2d56390fdfa30c5e
- https://git.kernel.org/stable/c/272bfb019f3cc018f654b992115774e77b4f3ffc
- https://git.kernel.org/stable/c/5bcf0dcbf9066348058b88a510c57f70f384c92c
- https://git.kernel.org/stable/c/6fd81f9d333e7b3532036577b1beb74ba1323553
- https://git.kernel.org/stable/c/e22e25820fa04ea5eaac4ef7ee200e9923f466a4