gzip: do not store timestamp in gzip header

Storing the original file's modification time in the output file is
harmful (precludes deterministic results) and unlike official gzip,
the busybox version provides no way to suppress this behavior; the -n
option is silently ignored. Rather than trying to make -n work, this
patch just removes the timestamp-storing functionality. It should be
considered deprecated anyway; it's not Y2038-safe and gunzip ignores
it by default.

Per RFC 1952, 0 is the correct value to store to indicate that there
is no timestamp.

Signed-off-by: Rich Felker <dalias@libc.org>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 16 insertions, 4 deletions

diff --git a/archival/gzip.c b/archival/gzip.c
index a93d2175a..46367f9e6 100644
--- a/archival/gzip.c
+++ b/archival/gzip.c
@@ -2007,7 +2007,7 @@ static void ct_init(void)
  * IN assertions: the input and output buffers are cleared.
  */
 
-static void zip(ulg time_stamp)
+static void zip(void)
 {
         ush deflate_flags = 0;  /* pkzip -es, -en or -ex equivalent */
 
@@ -2018,7 +2018,7 @@ static void zip(ulg time_stamp)
         /* compression method: 8 (DEFLATED) */
         /* general flags: 0 */
         put_32bit(0x00088b1f);
-        put_32bit(time_stamp);
+        put_32bit(0);           /* Unix timestamp */
 
         /* Write deflated file to zip file */
         G1.crc = ~0;
@@ -2044,8 +2044,6 @@ static void zip(ulg time_stamp)
 static
 IF_DESKTOP(long long) int FAST_FUNC pack_gzip(transformer_state_t *xstate UNUSED_PARAM)
 {
-        struct stat s;
-
         /* Clear input and output buffers */
         G1.outcnt = 0;
 #ifdef DEBUG
@@ -2077,9 +2075,23 @@ IF_DESKTOP(long long) int FAST_FUNC pack_gzip(transformer_state_t *xstate UNUSED
         G2.bl_desc.max_length  = MAX_BL_BITS;
         //G2.bl_desc.max_code    = 0;
 
+#if 0
+        /* Saving of timestamp is disabled. Why?
+         * - it is not Y2038-safe.
+         * - some people want deterministic results
+         *   (normally they'd use -n, but our -n is a nop).
+         * - it's bloat.
+         * Per RFC 1952, gzfile.time=0 is "no timestamp".
+         * If users will demand this to be reinstated,
+         * implement -n "don't save timestamp".
+         */
+        struct stat s;
         s.st_ctime = 0;
         fstat(STDIN_FILENO, &s);
         zip(s.st_ctime);
+#else
+        zip();
+#endif
         return 0;
 }