Improve unzip's handling of stream ZIP files

Search harder for the ZIP magic numbers at the end of a file by checking
16 KiB from the end instead of just 1 KiB.  ZIP files with long comments
(such as certain cryptographically signed files) or those sitting in a
wrapper could have more than 1 KiB of data after the magic numbers, so
they couldn't be read.

Signed-off-by: Dan Fandrich <dan@coneharvesters.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 9 insertions, 4 deletions

diff --git a/archival/unzip.c b/archival/unzip.c
index 1d3291ab8..84081c021 100644
--- a/archival/unzip.c
+++ b/archival/unzip.c
@@ -150,23 +150,26 @@ enum { zip_fd = 3 };
 
 
 #if ENABLE_DESKTOP
+
+#define PEEK_FROM_END 16384
+
 /* NB: does not preserve file position! */
 static uint32_t find_cdf_offset(void)
 {
-        unsigned char buf[1024];
         cde_header_t cde_header;
         unsigned char *p;
         off_t end;
+        unsigned char *buf = xzalloc(PEEK_FROM_END);
 
         end = xlseek(zip_fd, 0, SEEK_END);
-        end -= 1024;
+        end -= PEEK_FROM_END;
         if (end < 0)
                 end = 0;
         xlseek(zip_fd, end, SEEK_SET);
-        full_read(zip_fd, buf, 1024);
+        full_read(zip_fd, buf, PEEK_FROM_END);
 
         p = buf;
-        while (p <= buf + 1024 - CDE_HEADER_LEN - 4) {
+        while (p <= buf + PEEK_FROM_END - CDE_HEADER_LEN - 4) {
                 if (*p != 'P') {
                         p++;
                         continue;
@@ -180,8 +183,10 @@ static uint32_t find_cdf_offset(void)
                 /* we found CDE! */
                 memcpy(cde_header.raw, p + 1, CDE_HEADER_LEN);
                 FIX_ENDIANNESS_CDE(cde_header);
+                free(buf);
                 return cde_header.formatted.cdf_offset;
         }
+        //free(buf);
         bb_error_msg_and_die("can't find file table");
 };