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THREATINT
PUBLISHED

CVE-2024-49861

bpf: Fix helper writes to read-only maps



AssignerLinux
Reserved2024-10-21
Published2024-10-21
Updated2024-11-05

Description

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.

Product status

Default status
unaffected

57c3bb725a3d before a2c8dc7e2180
affected

57c3bb725a3d before 2ed98ee02d1e
affected

57c3bb725a3d before 1e75d2513315
affected

57c3bb725a3d before 32556ce93bc4
affected

Default status
affected

5.2
affected

Any version before 5.2
unaffected

6.6.54
unaffected

6.10.13
unaffected

6.11.2
unaffected

6.12-rc1
unaffected

References

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

cve.org CVE-2024-49861

nvd.nist.gov CVE-2024-49861

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