bzip2: fix two crashes on corrupted archives

As it turns out, longjmp'ing into freed stack is not healthy...

function                                             old     new   delta
unpack_usage_messages                                  -      97     +97
unpack_bz2_stream                                    369     409     +40
get_next_block                                      1667    1677     +10
get_bits                                             156     155      -1
start_bunzip                                         212     183     -29
bb_show_usage                                        181     120     -61
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 2/3 up/down: 147/-91)            Total: 56 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 12 insertions, 5 deletions

diff --git a/libbb/appletlib.c b/libbb/appletlib.c
index 022455da4..769b7881c 100644
--- a/libbb/appletlib.c
+++ b/libbb/appletlib.c
@@ -102,14 +102,21 @@ static const char *unpack_usage_messages(void)
         char *outbuf = NULL;
         bunzip_data *bd;
         int i;
+        jmp_buf jmpbuf;
 
-        i = start_bunzip(&bd,
+        /* Setup for I/O error handling via longjmp */
+        i = setjmp(jmpbuf);
+        if (i == 0) {
+                i = start_bunzip(&jmpbuf,
+                        &bd,
                         /* src_fd: */ -1,
                         /* inbuf:  */ packed_usage,
-                        /* len:    */ sizeof(packed_usage));
-        /* read_bunzip can longjmp to start_bunzip, and ultimately
-         * end up here with i != 0 on read data errors! Not trivial */
-        if (!i) {
+                        /* len:    */ sizeof(packed_usage)
+                );
+        }
+        /* read_bunzip can longjmp and end up here with i != 0
+         * on read data errors! Not trivial */
+        if (i == 0) {
                 /* Cannot use xmalloc: will leak bd in NOFORK case! */
                 outbuf = malloc_or_warn(sizeof(UNPACKED_USAGE));
                 if (outbuf)