GHSA-qwgh-2vcv-g2f7 block_buffer: panic corrupts inline buffer position

• crates.io block_buffer: >= 0.11.0, < 0.12.1 → fixed in 0.12.1

Summary A caught panic may leave the cursor position of `EagerBuffer` or `ReadBuffer` in a corrupted state; this in turn allows out-of-bounds reads/writes. Details & PoC The following two tests fail miri: ```rust [cfg(miri)] [test] fn eager_digest_blocks_panic_corrupts_inline_position() { // `EagerBuffer` stores its cursor in the last byte of the internal block. // When `digest_blocks` completes a previously partial block, it overwrites // that byte with input data before invoking the caller-provided `compress` // callback. If the callback panics, safe code can catch the panic and keep // using the buffer while its cursor byte no longer satisfies the internal // `pos ::new(&[1, 2]); let _ = std::panic::catch_unwind(std::panic::AssertUnwindSafe(|| { buf.digest_blocks(&[3, 0xff], |_| panic!("simulated compression failure")); })); let _ = buf.get_pos(); } [cfg(miri)] [test] fn read_buffer_generator_panic_corrupts_inline_position() { // `ReadBuffer` stores its cursor in `buffer[0]`, but `write_block` gives // `gen_block` mutable access to the whole internal block before restoring // `buffer[0]` to a valid cursor. If `gen_block` writes an arbitrary first // byte and panics, safe code can catch the panic and later observe an // invalid cursor. Under Miri this `get_pos` call reaches the // `unreachable_unchecked` used for the assumed-valid cursor. let mut buf = ReadBuffer::::default(); let _ = std::panic::catch_unwind(std::panic::AssertUnwindSafe(|| { buf.write_block( 1, |block| { block[0] = 0xff; panic!("simulated block generation failure"); }, |_| {}, ); })); let _ = buf.get_pos(); } ``` They fail on an `unreachable_unchecked!()` under the invariant for the `pos` to always be within bounds of the block. Impact While the byte that overwrites `pos` may come from untrusted input and is therefore attacker-controlled, this still relies on the surrounding code catching the panic and carrying on, which should be uncommon in practice. For this to be exploitable, the attacker also needs a way to trigger a panic here; I have not investigated how feasible that is. Credits The issue was discovered by GPT-5.5