Add advisory for git2: DiffBinaryFile::data() for empty data triggers UB

Author: DanielEScherzer

crates/git2/RUSTSEC-0000-0000.md

@@ -0,0 +1,16 @@
+```toml
+[advisory]
+id = "RUSTSEC-0000-0000"
+package = "git2"
+date = "2026-06-12"
+url = "https://github.com/rust-lang/git2-rs/pull/1279"
+informational = "unsound"
+keywords = ["git2"]
+
+[versions]
+patched = ["> 0.21.0"]
+```
+
+# Potential undefined behavior when calling DiffBinaryFile::data()
+
+Git diffs with binary file changes do not always include the raw data of such changes, but sometimes just report *that* a change was made (e.g. with a line `Binary files /dev/null and b/binary.pdf differ` for a new file addition). When examining such a diff, `DiffBinaryFile::data()` caused git2 to pass a null pointer to the unsafe function `slice::from_raw_parts()`. Based on the safety section documentation of function, data must be non-null even for slices of length zero. Thus, the use of a null pointer leads to undefined behavior.