tar: cry murder and bail out if file shrinks under us while we tar it up

2 files changed, 13 insertions, 4 deletions

diff --git a/archival/tar.c b/archival/tar.c
index 6aaa42273..99c4adb6a 100644
--- a/archival/tar.c
+++ b/archival/tar.c
@@ -59,7 +59,7 @@ struct TarHeader {		  /* byte offset */
 typedef struct TarHeader TarHeader;
 
 /*
-** writeTarFile(),  writeFileToTarball(), and writeTarHeader() are
+** writeTarFile(), writeFileToTarball(), and writeTarHeader() are
 ** the only functions that deal with the HardLinkInfo structure.
 ** Even these functions use the xxxHardLinkInfo() functions.
 */
@@ -397,7 +397,17 @@ static int writeFileToTarball(const char *fileName, struct stat *statbuf,
                 off_t readSize = 0;
 
                 /* write the file to the archive */
-                readSize = bb_copyfd_eof(inputFileFd, tbInfo->tarFd);
+                readSize = bb_copyfd_size(inputFileFd, tbInfo->tarFd, statbuf->st_size);
+                if (readSize != statbuf->st_size) {
+                        /* Deadly. We record size into header first, */
+                        /* and then write out file. If file shrinks in between, */
+                        /* tar will be corrupted. So bail out. */
+                        /* NB: GNU tar 1.16 warns and pads with zeroes */
+                        /* or even seeks back and updates header */
+                        bb_error_msg_and_die("short read from %s", fileName);
+                }
+                /* Check that file did not grow in between? */
+                /* if (safe_read(inputFileFd,1) == 1) warn but continue? */
                 close(inputFileFd);
 
                 /* Pad the file up to the tar block size */
diff --git a/libbb/copyfd.c b/libbb/copyfd.c
index 87126eb72..601c51ce4 100644
--- a/libbb/copyfd.c
+++ b/libbb/copyfd.c
@@ -46,8 +46,7 @@ static off_t bb_full_fd_action(int src_fd, int dst_fd, off_t size)
                 } else if (rd < 0) {
                         bb_perror_msg(bb_msg_read_error);
                         break;
-                } else if (rd == 0) {
-                        /* All done. */
+                } else { /* eof - all done. */
                         status = 0;
                         break;
                 }