sys/fido2: fix CBOR parsing #17192
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sys/fido2: fix CBOR parsing #17192
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The TinyCBOR library takes a `size_t *` length argument in many functions which at function call contains the length of a buffer, and at exit the actual size of the data. The FIDO-2 code however uses `uint8_t` fields in `struct`s to store the data. Previously, a pointer to that `uint8_t` filed was just casted to `size_t *`, resulting in three neighboring bytes also being interpreted as being part of the buffer size - which could result in undetected buffer overflows. Similar, upon exit of the function not only the `uint8_t` sized length `struct` member but also three neighboring bytes were written to. I didn't care to investigate, but this really looks like crafted CBOR payloads send to the FIDO2 implementation could result in arbitrary code execution on the device.
benpicco
approved these changes
Nov 13, 2021
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thanks for the quick review! |
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Backport provided in #17193 |
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Contribution description
The TinyCBOR library takes a
size_t *length argument in many functions which at function call contains the length of a buffer, and at exit the actual size of the data. The FIDO-2 code however usesuint8_tfields instructs to store the data. Previously, a pointer to thatuint8_tfiled was just casted tosize_t *, resulting in three neighboring bytes also being interpreted as being part of the buffer size - which could result in undetected buffer overflows. Similar, upon exit of the function not only theuint8_tsized lengthstructmember but also three neighboring bytes were written to.I didn't care to investigate, but this really looks like crafted CBOR payloads send to the FIDO2 implementation could result in arbitrary code execution on the device.
Testing procedure
Normal operation should still work.
Issues/PRs references
Detected by #14955