From a5b16a54a5b7b7d8bd04e504e6c99da8c142f0b8 Mon Sep 17 00:00:00 2001
From: delphij <delphij@FreeBSD.org>
Date: Sat, 14 Mar 2020 05:57:22 +0000
Subject: [PATCH] Remove unneeded checks for prelen.

In order to determine the type of a compressed file, we have to read
in the first four bytes which may also be important for decompression
purposes, to do that we would pass the buffer that we have already
read in, along with the size of it.

Rename header1 to fourbytes to make that explicit, and remove all
checks for prelen.

Reported by:	cem
Reviewed by:	cem
MFC after:	2 weeks
Differential Revision:	https://reviews.freebsd.org/D24034
---
 usr.bin/gzip/gzip.c   | 34 +++++++++++++++++-----------------
 usr.bin/gzip/unlz.c   |  2 --
 usr.bin/gzip/unpack.c |  3 ---
 3 files changed, 17 insertions(+), 22 deletions(-)

diff --git a/usr.bin/gzip/gzip.c b/usr.bin/gzip/gzip.c
index b348733eee6b..47cfd225b844 100644
--- a/usr.bin/gzip/gzip.c
+++ b/usr.bin/gzip/gzip.c
@@ -1443,7 +1443,7 @@ file_uncompress(char *file, char *outfile, size_t outsize)
 	struct stat isb, osb;
 	off_t size;
 	ssize_t rbytes;
-	unsigned char header1[4];
+	unsigned char fourbytes[4];
 	enum filetype method;
 	int fd, ofd, zfd = -1;
 	int error;
@@ -1477,8 +1477,8 @@ file_uncompress(char *file, char *outfile, size_t outsize)
 		goto lose;
 	}
 
-	rbytes = read(fd, header1, sizeof header1);
-	if (rbytes != sizeof header1) {
+	rbytes = read(fd, fourbytes, sizeof fourbytes);
+	if (rbytes != sizeof fourbytes) {
 		/* we don't want to fail here. */
 #ifndef SMALL
 		if (fflag)
@@ -1492,7 +1492,7 @@ file_uncompress(char *file, char *outfile, size_t outsize)
 	}
 	infile_newdata(rbytes);
 
-	method = file_gettype(header1);
+	method = file_gettype(fourbytes);
 #ifndef SMALL
 	if (fflag == 0 && method == FT_UNKNOWN) {
 		maybe_warnx("%s: not in gzip format", file);
@@ -1516,7 +1516,7 @@ file_uncompress(char *file, char *outfile, size_t outsize)
 		infile_newdata(rv);
 		timestamp = le32dec(&ts[0]);
 
-		if (header1[3] & ORIG_NAME) {
+		if (fourbytes[3] & ORIG_NAME) {
 			rbytes = pread(fd, name, sizeof(name) - 1, GZIP_ORIGNAME);
 			if (rbytes < 0) {
 				maybe_warn("can't read %s", file);
@@ -1818,7 +1818,7 @@ static void
 handle_stdin(void)
 {
 	struct stat isb;
-	unsigned char header1[4];
+	unsigned char fourbytes[4];
 	size_t in_size;
 	off_t usize, gsize;
 	enum filetype method;
@@ -1849,16 +1849,16 @@ handle_stdin(void)
 		goto out;
 	}
 
-	bytes_read = read_retry(STDIN_FILENO, header1, sizeof header1);
+	bytes_read = read_retry(STDIN_FILENO, fourbytes, sizeof fourbytes);
 	if (bytes_read == -1) {
 		maybe_warn("can't read stdin");
 		goto out;
-	} else if (bytes_read != sizeof(header1)) {
+	} else if (bytes_read != sizeof(fourbytes)) {
 		maybe_warnx("(stdin): unexpected end of file");
 		goto out;
 	}
 
-	method = file_gettype(header1);
+	method = file_gettype(fourbytes);
 	switch (method) {
 	default:
 #ifndef SMALL
@@ -1866,17 +1866,17 @@ handle_stdin(void)
 			maybe_warnx("unknown compression format");
 			goto out;
 		}
-		usize = cat_fd(header1, sizeof header1, &gsize, STDIN_FILENO);
+		usize = cat_fd(fourbytes, sizeof fourbytes, &gsize, STDIN_FILENO);
 		break;
 #endif
 	case FT_GZIP:
 		usize = gz_uncompress(STDIN_FILENO, STDOUT_FILENO,
-			      (char *)header1, sizeof header1, &gsize, "(stdin)");
+			      (char *)fourbytes, sizeof fourbytes, &gsize, "(stdin)");
 		break;
 #ifndef NO_BZIP2_SUPPORT
 	case FT_BZIP2:
 		usize = unbzip2(STDIN_FILENO, STDOUT_FILENO,
-				(char *)header1, sizeof header1, &gsize);
+				(char *)fourbytes, sizeof fourbytes, &gsize);
 		break;
 #endif
 #ifndef NO_COMPRESS_SUPPORT
@@ -1886,27 +1886,27 @@ handle_stdin(void)
 			goto out;
 		}
 
-		usize = zuncompress(in, stdout, (char *)header1,
-		    sizeof header1, &gsize);
+		usize = zuncompress(in, stdout, (char *)fourbytes,
+		    sizeof fourbytes, &gsize);
 		fclose(in);
 		break;
 #endif
 #ifndef NO_PACK_SUPPORT
 	case FT_PACK:
 		usize = unpack(STDIN_FILENO, STDOUT_FILENO,
-			       (char *)header1, sizeof header1, &gsize);
+			       (char *)fourbytes, sizeof fourbytes, &gsize);
 		break;
 #endif
 #ifndef NO_XZ_SUPPORT
 	case FT_XZ:
 		usize = unxz(STDIN_FILENO, STDOUT_FILENO,
-			     (char *)header1, sizeof header1, &gsize);
+			     (char *)fourbytes, sizeof fourbytes, &gsize);
 		break;
 #endif
 #ifndef NO_LZ_SUPPORT
 	case FT_LZ:
 		usize = unlz(STDIN_FILENO, STDOUT_FILENO,
-			     (char *)header1, sizeof header1, &gsize);
+			     (char *)fourbytes, sizeof fourbytes, &gsize);
 		break;
 #endif
 	}
diff --git a/usr.bin/gzip/unlz.c b/usr.bin/gzip/unlz.c
index f3c20ecb0f49..0bfea3f439d3 100644
--- a/usr.bin/gzip/unlz.c
+++ b/usr.bin/gzip/unlz.c
@@ -618,8 +618,6 @@ unlz(int fin, int fout, char *pre, size_t prelen, off_t *bytes_in)
 
 	char header[HDR_SIZE];
 
-	if (prelen > sizeof(header))
-		return -1;
 	if (pre && prelen)
 		memcpy(header, pre, prelen);
 	
diff --git a/usr.bin/gzip/unpack.c b/usr.bin/gzip/unpack.c
index 5ddb8d3fdf86..2ebfaf108be4 100644
--- a/usr.bin/gzip/unpack.c
+++ b/usr.bin/gzip/unpack.c
@@ -156,9 +156,6 @@ unpack_parse_header(int in, int out, char *pre, size_t prelen, off_t *bytes_in,
 	ssize_t bytesread;		/* Bytes read from the file */
 	int i, j, thisbyte;
 
-	if (prelen > sizeof hdr)
-		maybe_err("prelen too long");
-
 	/* Prepend the header buffer if we already read some data */
 	if (prelen != 0)
 		memcpy(hdr, pre, prelen);