gzip: fix compression level bug. Closes 9131

fix broken logic to get the gzip_level_config value from options -1 to
-9.

This fixes an off-by-one bug that caused gzip -9 output bigger files
than the other compression levels.

It fixes so that compression level 1 to 3 are actually mapped to level 4
as comments say.

It also fixes that levels -4 to -9 is mapped to correct level and avoids
out-of-bounds access.

Signed-off-by: Natanael Copa <ncopa@alpinelinux.org>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

diff --git a/archival/gzip.c b/archival/gzip.c
index 8f1e4ff2961ebde9b6fe2605e4ee0b3d1a9eb526..9e0bee8153eb82450b68e0b3f9fba8f501fb2e20 100644 (file)
--- a/archival/gzip.c
+++ b/archival/gzip.c
@@ -2220,10 +2220,7 @@ int gzip_main(int argc UNUSED_PARAM, char **argv)
        opt >>= ENABLE_GUNZIP ? 7 : 5; /* drop cfv[dt]qn bits */
        if (opt == 0)
                opt = 1 << 6; /* default: 6 */
-       /* Map 1..3 to 4 */
-       if (opt & 0x7)
-               opt |= 1 << 4;
-       opt = ffs(opt >> 3);
+       opt = ffs(opt >> 4); /* Maps -1..-4 to [0], -5 to [1] ... -9 to [5] */
        max_chain_length = 1 << gzip_level_config[opt].chain_shift;
        good_match       = gzip_level_config[opt].good;
        max_lazy_match   = gzip_level_config[opt].lazy2 * 2;