unzip: fix a case where we find wrong CDE. Closes 8821

function                                             old     new   delta
unzip_main                                          2472    2490     +18

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

1 files changed, 35 insertions, 8 deletions

diff --git a/archival/unzip.c b/archival/unzip.c
index f41ab6f44..b0a6ca836 100644
--- a/archival/unzip.c
+++ b/archival/unzip.c
@@ -45,6 +45,12 @@
 #include "libbb.h"
 #include "bb_archive.h"
 
+#if 0
+# define dbg(...) bb_error_msg(__VA_ARGS__)
+#else
+# define dbg(...) ((void)0)
+#endif
+
 enum {
 #if BB_BIG_ENDIAN
         ZIP_FILEHEADER_MAGIC = 0x504b0304,
@@ -193,15 +199,17 @@ static uint32_t find_cdf_offset(void)
         unsigned char *p;
         off_t end;
         unsigned char *buf = xzalloc(PEEK_FROM_END);
+        uint32_t found;
 
         end = xlseek(zip_fd, 0, SEEK_END);
         end -= PEEK_FROM_END;
         if (end < 0)
                 end = 0;
-        xlseek(zip_fd, end, SEEK_SET);
+        dbg("Looking for cdf_offset starting from 0x%"OFF_FMT"x", end);
+        xlseek(zip_fd, end, SEEK_SET);
         full_read(zip_fd, buf, PEEK_FROM_END);
 
-        cde_header.formatted.cdf_offset = BAD_CDF_OFFSET;
+        found = BAD_CDF_OFFSET;
         p = buf;
         while (p <= buf + PEEK_FROM_END - CDE_HEADER_LEN - 4) {
                 if (*p != 'P') {
@@ -220,14 +228,25 @@ static uint32_t find_cdf_offset(void)
                 /*
                  * I've seen .ZIP files with seemingly valid CDEs
                  * where cdf_offset points past EOF - ??
-                 * Ignore such CDEs:
+                 * This check ignores such CDEs:
                  */
-                if (cde_header.formatted.cdf_offset < end + (p - buf))
-                        break;
-                cde_header.formatted.cdf_offset = BAD_CDF_OFFSET;
+                if (cde_header.formatted.cdf_offset < end + (p - buf)) {
+                        found = cde_header.formatted.cdf_offset;
+                        dbg("Possible cdf_offset:0x%x at 0x%"OFF_FMT"x",
+                                (unsigned)found, end + (p-3 - buf));
+                        dbg("  cdf_offset+cdf_size:0x%x",
+                                (unsigned)(found + SWAP_LE32(cde_header.formatted.cdf_size)));
+                        /*
+                         * We do not "break" here because only the last CDE is valid.
+                         * I've seen a .zip archive which contained a .zip file,
+                         * uncompressed, and taking the first CDE was using
+                         * the CDE inside that file!
+                         */
+                }
         }
         free(buf);
-        return cde_header.formatted.cdf_offset;
+        dbg("Found cdf_offset:0x%x", (unsigned)found);
+        return found;
 };
 
 static uint32_t read_next_cdf(uint32_t cdf_offset, cdf_header_t *cdf_ptr)
@@ -240,9 +259,13 @@ static uint32_t read_next_cdf(uint32_t cdf_offset, cdf_header_t *cdf_ptr)
                 cdf_offset = find_cdf_offset();
 
         if (cdf_offset != BAD_CDF_OFFSET) {
+                dbg("Reading CDF at 0x%x", (unsigned)cdf_offset);
                 xlseek(zip_fd, cdf_offset + 4, SEEK_SET);
                 xread(zip_fd, cdf_ptr->raw, CDF_HEADER_LEN);
                 FIX_ENDIANNESS_CDF(*cdf_ptr);
+                dbg("file_name_length:%u", (unsigned)cdf_ptr->formatted.file_name_length);
+                dbg("extra_field_length:%u", (unsigned)cdf_ptr->formatted.extra_field_length);
+                dbg("file_comment_length:%u", (unsigned)cdf_ptr->formatted.file_comment_length);
                 cdf_offset += 4 + CDF_HEADER_LEN
                         + cdf_ptr->formatted.file_name_length
                         + cdf_ptr->formatted.extra_field_length
@@ -532,11 +555,14 @@ int unzip_main(int argc, char **argv)
                 /* Check magic number */
                 xread(zip_fd, &magic, 4);
                 /* Central directory? It's at the end, so exit */
-                if (magic == ZIP_CDF_MAGIC)
+                if (magic == ZIP_CDF_MAGIC) {
+                        dbg("got ZIP_CDF_MAGIC");
                         break;
+                }
 #if ENABLE_DESKTOP
                 /* Data descriptor? It was a streaming file, go on */
                 if (magic == ZIP_DD_MAGIC) {
+                        dbg("got ZIP_DD_MAGIC");
                         /* skip over duplicate crc32, cmpsize and ucmpsize */
                         unzip_skip(3 * 4);
                         continue;
@@ -544,6 +570,7 @@ int unzip_main(int argc, char **argv)
 #endif
                 if (magic != ZIP_FILEHEADER_MAGIC)
                         bb_error_msg_and_die("invalid zip magic %08X", (int)magic);
+                dbg("got ZIP_FILEHEADER_MAGIC");
 
                 /* Read the file header */
                 xread(zip_fd, zip_header.raw, ZIP_HEADER_LEN);