fix(zseri/store-ref-scanner): no_std support and runtime panics r/3385

This also changes the fuzzing infrastructure from proptest to cargo-fuzz,
and this lead to the discovery of two mishandlings of edge-cases:

* when a "path_to_store" is at the end of the input, it tried to access
  the input slice out-of-bounds (the `just_store` test covers that now)
* non-ASCII characters lead to an out-of-bounds access in HalfBytesMask
  (the `non_ascii` test covers that now)

Change-Id: Icaa2518dcd93e1789a2c0da4cf0fec46016d3bad
Reviewed-on: https://cl.tvl.fyi/c/depot/+/4604
Tested-by: BuildkiteCI
Reviewed-by: zseri <zseri.devel@ytrizja.de>

3 files changed, 59 insertions, 52 deletions

diff --git a/users/zseri/store-ref-scanner/src/hbm.rs b/users/zseri/store-ref-scanner/src/hbm.rs
index 881f1dfdeb..c2fd2950d5 100644
--- a/users/zseri/store-ref-scanner/src/hbm.rs
+++ b/users/zseri/store-ref-scanner/src/hbm.rs
@@ -1,8 +1,7 @@
 #[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
 pub struct HalfBytesMask(pub [u8; 16]);
 
-// fires erronously
-#[allow(clippy::zero_prefixed_literal)]
+#[allow(clippy::as_conversions, clippy::zero_prefixed_literal)]
 impl HalfBytesMask {
     pub const B32_REVSHA256: HalfBytesMask =
         HalfBytesMask([0, 0, 0, 0, 0, 0, 255, 3, 0, 0, 0, 0, 222, 127, 207, 7]);
@@ -11,6 +10,10 @@ impl HalfBytesMask {
         0, 0, 0, 0, 0, 8, 255, 3, 254, 255, 255, 135, 254, 255, 255, 7,
     ]);
 
+    pub const DFL_REST: HalfBytesMask = HalfBytesMask([
+        0, 0, 0, 0, 0, 104, 255, 163, 254, 255, 255, 135, 254, 255, 255, 7,
+    ]);
+
     #[inline]
     #[proc_unroll::unroll]
     pub const fn from_expanded(x: [bool; 128]) -> Self {
@@ -51,7 +54,11 @@ impl HalfBytesMask {
     }
 
     pub fn contains(&self, byte: u8) -> bool {
-        (self.0[usize::from(byte / 8)] >> u32::from(byte % 8)) & 0b1 != 0
+        if byte >= 0x80 {
+            false
+        } else {
+            (self.0[usize::from(byte / 8)] >> u32::from(byte % 8)) & 0b1 != 0
+        }
     }
 
     pub fn set(&mut self, byte: u8, allow: bool) {
@@ -96,6 +103,13 @@ mod tests {
     }
 
     #[test]
+    fn non_ascii() {
+        for i in 0x80..=0xff {
+            assert!(!HalfBytesMask::DFL_REST.contains(i));
+        }
+    }
+
+    #[test]
     fn dflmask() {
         assert_eq!(
             HalfBytesMask::from_expanded(
@@ -138,15 +152,12 @@ mod tests {
             ),
             HalfBytesMask::B64_BLAKE2B256,
         );
-    }
 
-    proptest::proptest! {
-        #[test]
-        fn hbm_roundtrip(s: [u8; 16]) {
-            let a = HalfBytesMask(s);
-            let b = a.into_expanded();
-            let c = HalfBytesMask::from_expanded(b);
-            assert_eq!(a, c);
-        }
+        assert_eq!(
+            HalfBytesMask::from_bytes(
+                b"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+-._?="
+            ),
+            HalfBytesMask::DFL_REST,
+        );
     }
 }
diff --git a/users/zseri/store-ref-scanner/src/lib.rs b/users/zseri/store-ref-scanner/src/lib.rs
index 63b3689978..ae1912c555 100644
--- a/users/zseri/store-ref-scanner/src/lib.rs
+++ b/users/zseri/store-ref-scanner/src/lib.rs
@@ -1,4 +1,6 @@
-// TODO: make this no_std if possible
+#![no_std]
+#![forbid(clippy::cast_ptr_alignment, trivial_casts, unconditional_recursion)]
+#![deny(clippy::as_conversions)]
 
 mod hbm;
 pub use hbm::HalfBytesMask;
@@ -34,7 +36,7 @@ impl ScannerInput for &mut [u8] {
     fn split_to(&mut self, at: usize) -> Self {
         // Lifetime dance taken from `impl Write for &mut [u8]`.
         // Taken from crate `std`.
-        let (a, b) = std::mem::take(self).split_at_mut(at);
+        let (a, b) = core::mem::take(self).split_at_mut(at);
         *self = b;
         a
     }
@@ -50,14 +52,14 @@ impl ScannerInput for &mut [u8] {
 /// and implements an iterator interfaces which returns these as byte slices.
 pub struct StoreRefScanner<'x, Input: 'x> {
     input: Input,
-    spec: &'x StoreSpec,
+    spec: &'x StoreSpec<'x>,
 }
 
 impl<'x, Input> StoreRefScanner<'x, Input>
 where
     Input: ScannerInput + 'x,
 {
-    pub fn new(input: Input, spec: &'x StoreSpec) -> Self {
+    pub fn new(input: Input, spec: &'x StoreSpec<'x>) -> Self {
         for i in [&spec.valid_hashbytes, &spec.valid_restbytes] {
             for j in [b'\0', b' ', b'\t', b'\n', b'/', b'\\'] {
                 assert!(!i.contains(j));
@@ -74,11 +76,10 @@ where
     type Item = Input;
 
     fn next(&mut self) -> Option<Input> {
-        let empty_path = camino::Utf8Path::new("");
         let hbl: usize = self.spec.hashbytes_len.into();
         while !self.input.as_ref().is_empty() {
-            if self.spec.path_to_store != empty_path {
-                let p2sas = self.spec.path_to_store.as_str();
+            if !self.spec.path_to_store.is_empty() {
+                let p2sas = self.spec.path_to_store;
                 if self.input.as_ref().starts_with(p2sas.as_bytes()) {
                     self.input.split_to(p2sas.len());
                 } else {
@@ -87,6 +88,9 @@ where
                 }
             }
             let hsep = matches!(self.input.as_ref().iter().next(), Some(b'/') | Some(b'\\'));
+            if self.input.as_ref().is_empty() {
+                break;
+            }
             self.input.split_to(1);
             if hsep && self.spec.check_rest(self.input.as_ref()) {
                 // we have found a valid hash
@@ -114,6 +118,8 @@ where
 #[cfg(test)]
 mod tests {
     use super::*;
+    extern crate alloc;
+    use alloc::{vec, vec::Vec};
 
     #[test]
     fn simple_nix2() {
@@ -121,7 +127,7 @@ mod tests {
             Derive([("out","","r:sha256","")],[("/nix/store/2ax7bvjdfkzim69q957i0jlg0nvmapg0-util-linux-2.37.2.drv",["dev"]),("/nix/store/6b55ssmh8pzqsc4q4kw1yl3kqvr4fvqj-bash-5.1-p12.drv",["out"]),("/nix/store/fp2vx24kczlzv84avds28wyzsmrn8kyv-source.drv",["out"]),("/nix/store/s6c2lm5hpsvdwnxq9y1g3ngncghjzc3k-stdenv-linux.drv",["out"]),("/nix/store/xlnzpf4mzghi8vl0krabrgcbnqk5qjf3-pkg-config-wrapper-0.29.2.drv",["out"])],["/nix/store/03sl46khd8gmjpsad7223m32ma965vy9-fix-static.patch","/nix/store/2q3z7587yhlz0i2xvfvvap42zk5carlv-bcache-udev-modern.patch","/nix/store/9krlzvny65gdc8s7kpb6lkx8cd02c25b-default-builder.sh"],"x86_64-linux","/0g15yibzzi3rmw29gqlbms05x9dbghbvh61v1qggydvmzh3bginw/bin/bash",["-e","/nix/store/9krlzvny65gdc8s7kpb6lkx8cd02c25b-default-builder.sh"],[("buildInputs","/0sdk1r4l43yw4g6lmqdhd92vhdfhlwz3m76jxzvzsqsv63czw2km"),("builder","/0g15yibzzi3rmw29gqlbms05x9dbghbvh61v1qggydvmzh3bginw/bin/bash"),("configureFlags",""),("depsBuildBuild",""),("depsBuildBuildPropagated",""),("depsBuildTarget",""),("depsBuildTargetPropagated",""),("depsHostHost",""),("depsHostHostPropagated",""),("depsTargetTarget",""),("depsTargetTargetPropagated",""),("doCheck",""),("doInstallCheck",""),("makeFlags","PREFIX=/1rz4g4znpzjwh1xymhjpm42vipw92pr73vdgl6xs1hycac8kf2n9 UDEVLIBDIR=/1rz4g4znpzjwh1xymhjpm42vipw92pr73vdgl6xs1hycac8kf2n9/lib/udev/"),("name","bcache-tools-1.0.7"),("nativeBuildInputs","/1kw0rwgdyq9q69wmmsa5d2kap6p52b0yldbzi4w17bhcq5g5cp2f"),("out","/1rz4g4znpzjwh1xymhjpm42vipw92pr73vdgl6xs1hycac8kf2n9"),("outputHashAlgo","sha256"),("outputHashMode","recursive"),("outputs","out"),("patches","/nix/store/2q3z7587yhlz0i2xvfvvap42zk5carlv-bcache-udev-modern.patch /nix/store/03sl46khd8gmjpsad7223m32ma965vy9-fix-static.patch"),("pname","bcache-tools"),("preBuild","sed -e \"s|/bin/sh|/0g15yibzzi3rmw29gqlbms05x9dbghbvh61v1qggydvmzh3bginw/bin/sh|\" -i *.rules\n"),("preInstall","mkdir -p \"$out/sbin\" \"$out/lib/udev/rules.d\" \"$out/share/man/man8\"\n"),("prePatch","sed -e \"/INSTALL.*initramfs\\/hook/d\" \\\n    -e \"/INSTALL.*initcpio\\/install/d\" \\\n    -e \"/INSTALL.*dracut\\/module-setup.sh/d\" \\\n    -e \"s/pkg-config/$PKG_CONFIG/\" \\\n    -i Makefile\n"),("propagatedBuildInputs",""),("propagatedNativeBuildInputs",""),("src","/nix/store/6izcafvfcbz19chi7hl20834g0fa043n-source"),("stdenv","/01ncyv8bxibj0imgfvmxgqy648n697bachil6aw6i46g1jk0bbds"),("strictDeps",""),("system","x86_64-linux"),("version","1.0.7")])
         "#;
         // we convert everything into strings because it is way easier to compare elements in error messages
-        let refs: Vec<&str> = StoreRefScanner::new(drv, &*SPEC_DFL_NIX2)
+        let refs: Vec<&str> = StoreRefScanner::new(drv, &StoreSpec::DFL_NIX2)
             .map(|i| core::str::from_utf8(i).unwrap())
             .collect();
         let refs_expect: Vec<&[u8]> = vec![
@@ -168,7 +174,7 @@ mod tests {
             /yzixs/xvwEcXIob_rQynUEtQiQbwaDXEobTVKEGaBMir9oH9k:         unified diff output, ASCII text
             /yzixs/ZPvQbRJrtyeSITvW3FUZvw99hhNOO3CFqGgmWgScxcg:         ASCII text
         "#;
-        let refs: Vec<&str> = StoreRefScanner::new(fake, &*SPEC_DFL_YZIX1)
+        let refs: Vec<&str> = StoreRefScanner::new(fake, &StoreSpec::DFL_YZIX1)
             .map(|i| core::str::from_utf8(i).unwrap())
             .collect();
         let refs_expect: Vec<&[u8]> = vec![
@@ -198,15 +204,11 @@ mod tests {
         assert_eq!(refs, refs_expect);
     }
 
-    proptest::proptest! {
-        #[test]
-        fn nocrash_nix2(s: Vec<u8>) {
-            let _ = StoreRefScanner::new(&s[..], &*SPEC_DFL_NIX2).count();
-        }
-
-        #[test]
-        fn nocrash_yzix1(s: Vec<u8>) {
-            let _ = StoreRefScanner::new(&s[..], &*SPEC_DFL_YZIX1).count();
+    #[test]
+    fn just_store() {
+        for i in [&StoreSpec::DFL_NIX2, &StoreSpec::DFL_YZIX1] {
+            let refs: Vec<&[u8]> = StoreRefScanner::new(i.path_to_store.as_bytes(), i).collect();
+            assert!(refs.is_empty());
         }
     }
 }
diff --git a/users/zseri/store-ref-scanner/src/spec.rs b/users/zseri/store-ref-scanner/src/spec.rs
index 034779e8e8..79da0842c5 100644
--- a/users/zseri/store-ref-scanner/src/spec.rs
+++ b/users/zseri/store-ref-scanner/src/spec.rs
@@ -1,10 +1,8 @@
 use crate::hbm::HalfBytesMask;
-use camino::Utf8PathBuf;
-use once_cell::sync::Lazy;
 
-pub struct StoreSpec {
+pub struct StoreSpec<'path> {
     /// path to store without trailing slash
-    pub path_to_store: Utf8PathBuf,
+    pub path_to_store: &'path str,
 
     /// compressed map of allowed ASCII characters in hash part
     pub valid_hashbytes: HalfBytesMask,
@@ -16,7 +14,7 @@ pub struct StoreSpec {
     pub hashbytes_len: u8,
 }
 
-impl StoreSpec {
+impl StoreSpec<'_> {
     pub(crate) fn check_rest(&self, rest: &[u8]) -> bool {
         let hbl = self.hashbytes_len.into();
         rest.iter()
@@ -25,22 +23,18 @@ impl StoreSpec {
             .count()
             == hbl
     }
-}
 
-pub static SPEC_DFL_NIX2: Lazy<StoreSpec> = Lazy::new(|| StoreSpec {
-    path_to_store: "/nix/store".into(),
-    valid_hashbytes: HalfBytesMask::B32_REVSHA256,
-    valid_restbytes: HalfBytesMask::from_bytes(
-        b"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+-._?=",
-    ),
-    hashbytes_len: 32,
-});
+    pub const DFL_NIX2: StoreSpec<'static> = StoreSpec {
+        path_to_store: "/nix/store",
+        valid_hashbytes: HalfBytesMask::B32_REVSHA256,
+        valid_restbytes: HalfBytesMask::DFL_REST,
+        hashbytes_len: 32,
+    };
 
-pub static SPEC_DFL_YZIX1: Lazy<StoreSpec> = Lazy::new(|| StoreSpec {
-    path_to_store: "/yzixs".into(),
-    valid_hashbytes: HalfBytesMask::B64_BLAKE2B256,
-    valid_restbytes: HalfBytesMask::from_bytes(
-        b"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+-._?=",
-    ),
-    hashbytes_len: 43,
-});
+    pub const DFL_YZIX1: StoreSpec<'static> = StoreSpec {
+        path_to_store: "/yzixs",
+        valid_hashbytes: HalfBytesMask::B64_BLAKE2B256,
+        valid_restbytes: HalfBytesMask::DFL_REST,
+        hashbytes_len: 43,
+    };
+}