Commit e252e6c696192729e576fffbd26991bd4b19e434 | zig

author	Andrew Kelley <andrew@ziglang.org> 2025-08-14 16:08:06-07:00
committer	GitHub <noreply@github.com> 2025-08-14 16:08:06-07:00
log	e252e6c696192729e576fffbd26991bd4b19e434
tree	481c8137999a5a650066e2d5229b21b69cf23e76
parent	2761cc8be0ef89772a41cb0aaf512ac463aa5c23
parent	353cf1f671b9127e7f425aaf3dcba655117ee45b
signature	Signed by PGP key B5690EEEBB952194

zstd.Decompress: Treat a partial magic number as a failure

2 files changed, 18 insertions(+), 3 deletions(-)

lib/std/compress/zstd.zig+6

...	@@ -121,6 +121,12 @@ test Decompress {	...	@@ -121,6 +121,12 @@ test Decompress {
121	try testExpectDecompress(uncompressed, compressed19);	121	try testExpectDecompress(uncompressed, compressed19);
122	}	122	}
123		123
		124	test "partial magic number" {
		125	const input_raw =
		126	"\x28\xb5\x2f"; // 3 bytes of the 4-byte zstandard frame magic number
		127	try testExpectDecompressError(error.BadMagic, input_raw);
		128	}
		129
124	test "zero sized raw block" {	130	test "zero sized raw block" {
125	const input_raw =	131	const input_raw =
126	"\x28\xb5\x2f\xfd" ++ // zstandard frame magic number	132	"\x28\xb5\x2f\xfd" ++ // zstandard frame magic number

lib/std/compress/zstd/Decompress.zig+12-3

 @@ -17,7 +17,6 @@ const State = union(enum) {
     new_frame,
     in_frame: InFrame,
     skipping_frame: usize,
-    end,
     const InFrame = struct {
         frame: Frame,
 @@ -158,7 +157,18 @@ fn stream(r: *Reader, w: *Writer, limit: Limit) Reader.StreamError!usize {
     switch (d.state) {
         .new_frame => {
-            // Allow error.EndOfStream only on the frame magic.
+            // Only return EndOfStream when there are exactly 0 bytes remaining on the
+            // frame magic. Any partial magic bytes should be considered a failure.
+            in.fill(@sizeOf(Frame.Magic)) catch |err| switch (err) {
+                error.EndOfStream => {
+                    if (in.bufferedLen() != 0) {
+                        d.err = error.BadMagic;
+                        return error.ReadFailed;
+                    }
+                    return err;
+                },
+                else => |e| return e,
+            };
             const magic = try in.takeEnumNonexhaustive(Frame.Magic, .little);
             initFrame(d, w.buffer.len, magic) catch |err| {
                 d.err = err;
 @@ -192,7 +202,6 @@ fn stream(r: *Reader, w: *Writer, limit: Limit) Reader.StreamError!usize {
             if (remaining.* == 0) d.state = .new_frame;
             return 0;
         },
-        .end => return error.EndOfStream,
     }
 }