CVE-2024-49861: bpf: Fix helper writes to read-only maps
First published: Mon Oct 21 2024(Updated: )
In the Linux kernel, the following vulnerability has been resolved: bpf: Fix helper writes to read-only maps Lonial found an issue that despite user- and BPF-side frozen BPF map (like in case of .rodata), it was still possible to write into it from a BPF program side through specific helpers having ARG_PTR_TO_{LONG,INT} as arguments. In check_func_arg() when the argument is as mentioned, the meta->raw_mode is never set. Later, check_helper_mem_access(), under the case of PTR_TO_MAP_VALUE as register base type, it assumes BPF_READ for the subsequent call to check_map_access_type() and given the BPF map is read-only it succeeds. The helpers really need to be annotated as ARG_PTR_TO_{LONG,INT} | MEM_UNINIT when results are written into them as opposed to read out of them. The latter indicates that it's okay to pass a pointer to uninitialized memory as the memory is written to anyway. However, ARG_PTR_TO_{LONG,INT} is a special case of ARG_PTR_TO_FIXED_SIZE_MEM just with additional alignment requirement. So it is better to just get rid of the ARG_PTR_TO_{LONG,INT} special cases altogether and reuse the fixed size memory types. For this, add MEM_ALIGNED to additionally ensure alignment given these helpers write directly into the args via *<ptr> = val. The .arg*_size has been initialized reflecting the actual sizeof(*<ptr>). MEM_ALIGNED can only be used in combination with MEM_FIXED_SIZE annotated argument types, since in !MEM_FIXED_SIZE cases the verifier does not know the buffer size a priori and therefore cannot blindly write *<ptr> = val.
Credit: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
| Affected Software | Affected Version | How to fix |
|---|---|---|
| Linux Kernel | >=5.2<6.6.54 | |
| Linux Kernel | >=6.7<6.10.13 | |
| Linux Kernel | >=6.11<6.11.2 |
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Reference Links
- https://git.kernel.org/stable/c/988e55abcf7fdb8fc9a76a7cf3f4e939a4d4fb3a
- https://git.kernel.org/stable/c/a2c8dc7e21803257e762b0bf067fd13e9c995da0
- https://git.kernel.org/stable/c/2ed98ee02d1e08afee88f54baec39ea78dc8a23c
- https://git.kernel.org/stable/c/1e75d25133158b525e0456876e9bcfd6b2993fd5
- https://git.kernel.org/stable/c/32556ce93bc45c730829083cb60f95a2728ea48b
- https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2024-49861
- https://nvd.nist.gov/vuln/detail/CVE-2024-49861
- https://launchpad.net/bugs/cve/CVE-2024-49861
- https://security-tracker.debian.org/tracker/CVE-2024-49861
- https://ubuntu.com/security/CVE-2024-49861
Frequently Asked Questions
What is the severity of CVE-2024-49861?
CVE-2024-49861 has been classified as a medium severity vulnerability in the Linux kernel.
How do I fix CVE-2024-49861?
To fix CVE-2024-49861, you should update to the latest patched version of the Linux kernel as recommended by your distribution.
Which versions of the Linux kernel are affected by CVE-2024-49861?
CVE-2024-49861 affects Linux kernel versions from 5.2 through 6.6.54, 6.7 through 6.10.13, and 6.11 up to 6.11.2.
What does CVE-2024-49861 involve?
CVE-2024-49861 involves a bug that allows write access to read-only maps within the BPF framework of the Linux kernel.
Who identified CVE-2024-49861?
CVE-2024-49861 was identified by a researcher named Lonial.
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