txdb: Check GetKey() result when priming cursor #35784

pull 650DataNerd wants to merge 1 commits into bitcoin:master from 650DataNerd:fix-txdb-cursor-malformed-key changing 3 files +62 −5

650DataNerd commented at 12:11 PM on July 23, 2026: none

This fixes #35172.

CCoinsViewDB::Cursor() primed its cached key by calling GetKey() on the first database record but ignored its return value. A failed read leaves entry.key at its default-constructed value of DB_COIN, which is indistinguishable from a genuinely valid coin key, so Valid()/GetKey() on the returned cursor incorrectly report success.

This mirrors the same class of bug already fixed in CCoinsViewDBCursor::Next() (#7890); this PR applies the identical fix to Cursor()'s priming logic.

Added a regression test (txdb_tests.cpp) reproducing the exact failure from the issue, confirmed it fails before the fix and passes after. Ran the full unit test suite (773 test cases) with no regressions.

txdb: Check GetKey() result when priming cursor

CCoinsViewDB::Cursor() primed its cached key by calling GetKey()
on the first database record but ignored its return value. When
GetKey() fails to decode a malformed record, entry.key retains its
default-constructed value of DB_COIN, which is indistinguishable
from a genuinely valid coin key. As a result, Valid() and GetKey()
on the returned cursor incorrectly report success for a record that
was never actually read.

This mirrors the same class of bug already fixed in
CCoinsViewDBCursor::Next() (see #7890); this commit applies the
identical fix to Cursor()'s priming logic.

Fixes #35172

beaded80bf

DrahtBot added the label UTXO Db and Indexes on Jul 23, 2026
DrahtBot commented at 12:11 PM on July 23, 2026: contributor


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For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/35784.



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Possible places where named args for integral literals may be used (e.g. func(x, /*named_arg=*/0) in C++, and func(x, named_arg=0) in Python):
- Coin{CTxOut{1, CScript{}}, 1, false} in src/test/txdb_tests.cpp
<sup>2026-07-23 12:11:46</sup>
sedited commented at 12:17 PM on July 23, 2026: contributor

This is a duplicate of #35654 . If you are interested in the change, please consider reviewing the original pull request. Closing.
sedited closed this on Jul 23, 2026
650DataNerd commented at 12:21 PM on July 23, 2026: none

ooh yes, I see the similarity. thankyou

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#7890 master: `gettxoutsetinfo` -> crash #35172 txdb: Cursor warmup accepts malformed first coin key

txdb: Check GetKey() result when priming cursor #35784

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