Merge pull request #9880 from squeek502/deflate-construct-errors

deflate: Better Huffman.construct errors and error handling

Author: andrewrk

lib/std/compress/deflate.zig

@@ -45,7 +45,9 @@ const Huffman = struct {
 
     min_code_len: u16,
 
-    fn construct(self: *Huffman, code_length: []const u16) !void {
+    const ConstructError = error{ Oversubscribed, IncompleteSet };
+
+    fn construct(self: *Huffman, code_length: []const u16) ConstructError!void {
         for (self.count) |*val| {
             val.* = 0;
         }
@@ -70,7 +72,7 @@ const Huffman = struct {
             // Make sure the number of codes with this length isn't too high.
             left -= @as(isize, @bitCast(i16, val));
             if (left < 0)
-                return error.InvalidTree;
+                return error.Oversubscribed;
         }
 
         // Compute the offset of the first symbol represented by a code of a
@@ -125,6 +127,9 @@ const Huffman = struct {
 
         self.last_code = codes[PREFIX_LUT_BITS + 1];
         self.last_index = offset[PREFIX_LUT_BITS + 1] - self.count[PREFIX_LUT_BITS + 1];
+
+        if (left > 0)
+            return error.IncompleteSet;
     }
 };
 
@@ -324,7 +329,13 @@ pub fn InflateStream(comptime ReaderType: type) type {
                 try lencode.construct(len_lengths[0..]);
 
                 const dist_lengths = [_]u16{5} ** MAXDCODES;
-                try distcode.construct(dist_lengths[0..]);
+                distcode.construct(dist_lengths[0..]) catch |err| switch (err) {
+                    // This error is expected because we only compute distance codes
+                    // 0-29, which is fine since "distance codes 30-31 will never actually
+                    // occur in the compressed data" (from section 3.2.6 of RFC1951).
+                    error.IncompleteSet => {},
+                    else => return err,
+                };
             }
 
             self.hlen = &lencode;
@@ -359,7 +370,7 @@ pub fn InflateStream(comptime ReaderType: type) type {
                     lengths[val] = @intCast(u16, try self.readBits(3));
                 }
 
-                try lencode.construct(lengths[0..]);
+                lencode.construct(lengths[0..]) catch return error.InvalidTree;
             }
 
             // Read the length/literal and distance code length tables.
@@ -408,8 +419,24 @@ pub fn InflateStream(comptime ReaderType: type) type {
             if (lengths[256] == 0)
                 return error.MissingEOBCode;
 
-            try self.huffman_tables[0].construct(lengths[0..nlen]);
-            try self.huffman_tables[1].construct(lengths[nlen .. nlen + ndist]);
+            self.huffman_tables[0].construct(lengths[0..nlen]) catch |err| switch (err) {
+                error.Oversubscribed => return error.InvalidTree,
+                error.IncompleteSet => {
+                    // incomplete code ok only for single length 1 code
+                    if (nlen != self.huffman_tables[0].count[0] + self.huffman_tables[0].count[1]) {
+                        return error.InvalidTree;
+                    }
+                },
+            };
+            self.huffman_tables[1].construct(lengths[nlen .. nlen + ndist]) catch |err| switch (err) {
+                error.Oversubscribed => return error.InvalidTree,
+                error.IncompleteSet => {
+                    // incomplete code ok only for single length 1 code
+                    if (ndist != self.huffman_tables[1].count[0] + self.huffman_tables[1].count[1]) {
+                        return error.InvalidTree;
+                    }
+                },
+            };
 
             self.hlen = &self.huffman_tables[0];
             self.hdist = &self.huffman_tables[1];
@@ -684,8 +711,22 @@ test "distance past beginning of output stream" {
 
 test "inflateStream fuzzing" {
     // see https://github.com/ziglang/zig/issues/9842
-    try std.testing.expectError(error.EndOfStream, testInflate("\x950000"));
+    try std.testing.expectError(error.EndOfStream, testInflate("\x95\x90=o\xc20\x10\x86\xf30"));
     try std.testing.expectError(error.OutOfCodes, testInflate("\x950\x00\x0000000"));
+
+    // Huffman.construct errors
+    // lencode
+    try std.testing.expectError(error.InvalidTree, testInflate("\x950000"));
+    try std.testing.expectError(error.InvalidTree, testInflate("\x05000"));
+    // hlen
+    try std.testing.expectError(error.InvalidTree, testInflate("\x05\xea\x01\t\x00\x00\x00\x01\x00\\\xbf.\t\x00"));
+    // hdist
+    try std.testing.expectError(error.InvalidTree, testInflate("\x05\xe0\x01A\x00\x00\x00\x00\x10\\\xbf."));
+
+    // Huffman.construct -> error.IncompleteSet returns that shouldn't give error.InvalidTree
+    // (like the "empty distance alphabet" test but for ndist instead of nlen)
+    try std.testing.expectError(error.EndOfStream, testInflate("\x05\xe0\x01\t\x00\x00\x00\x00\x10\\\xbf\xce"));
+    try testInflate("\x15\xe0\x01\t\x00\x00\x00\x00\x10\\\xbf.0");
 }
 
 fn testInflate(data: []const u8) !void {