more fixes to tempfile writeback

Avoid overwriting symlinks with the temp file.

When renaming the temp file, restore the original file's permissions after.

diff --git a/sponge.c b/sponge.c
index dcd4abaaa37c30c00b15f3f0ef64391f90231a73..a02e0e737ceae80fe2eebe12289be801eb4085b2 100644 (file)
--- a/sponge.c
+++ b/sponge.c
@@ -199,7 +199,7 @@ static void write_buff_out(char* buff, size_t length, FILE *fd) {
        }
 }
 
-static void copy_tmpfile(FILE *tmpfile, FILE *outfd) {
+static void copy_tmpfile(FILE *tmpfile, FILE *outfile) {
        char buf[BUFF_SIZE];
        if (fseek(tmpfile, 0, SEEK_SET)) {
                perror("could to seek to start of temporary file");
@@ -207,7 +207,7 @@ static void copy_tmpfile(FILE *tmpfile, FILE *outfd) {
                exit(1);
        }
        while (fread(buf, BUFF_SIZE, 1, tmpfile) > 0) {
-               write_buff_out(buf, BUFF_SIZE, outfd);
+               write_buff_out(buf, BUFF_SIZE, outfile);
        }
        if (ferror(tmpfile)) {
                perror("read temporary file");
@@ -215,7 +215,7 @@ static void copy_tmpfile(FILE *tmpfile, FILE *outfd) {
                exit(1);
        }
        fclose(tmpfile);
-       fclose(outfd);
+       fclose(outfile);
 }
 
 FILE *open_tmpfile(void) {
@@ -247,7 +247,7 @@ int main (int argc, char **argv) {
        char *buf, *bufstart, *outname = NULL;
        size_t bufsize = BUFF_SIZE;
        size_t bufused = 0;
-       FILE *tmpfile = 0;
+       FILE *outfile, *tmpfile = 0;
        ssize_t i = 0;
        size_t mem_available = default_sponge_size();
 
@@ -293,41 +293,53 @@ int main (int argc, char **argv) {
                /* write whatever we have in memory to tmpfile */
                if (bufused) 
                        write_buff_tmp(bufstart, bufused, tmpfile);
-               fclose(tmpfile);
+               free(bufstart);
+               if (fflush(tmpfile) != 0) {
+                       perror("fflush");
+                       exit(1);
+               }
 
                if (outname) {
                        /* If it's a regular file, or does not yet exist,
                         * attempt a fast rename of the temp file. */
-                       if ((stat(outname, &statbuf) == 0 &&
-                            S_ISREG(statbuf.st_mode)) ||
-                           errno == ENOENT) {
-                               if (rename(tmpname, outname) != 0) {
-                                       /* Slow copy. */
-                                       FILE *outfd = fopen(outname, "w");
-                                               if (outfd < 0) {
-                                               perror("error opening output file");
-                                               exit(1);
-                                       }
-                                       copy_tmpfile(tmpfile, outfd);
+                       if (((lstat(outname, &statbuf) == 0 &&
+                             S_ISREG(statbuf.st_mode) &&
+                             ! S_ISLNK(statbuf.st_mode)
+                            ) || errno == ENOENT) &&
+                           rename(tmpname, outname) == 0) {
+                               /* Fix renamed file mode. */
+                               if (errno != ENOENT &&
+                                   chmod(outname, statbuf.st_mode) != 0) {
+                                       perror("chmod");
+                                       exit(1);
                                }
+                               return(0);
+                       }
+                       
+                       /* Fall back to slow copy. */
+                       outfile = fopen(outname, "w");
+                       if (!outfile) {
+                               perror("error opening output file");
+                               exit(1);
                        }
+                       copy_tmpfile(tmpfile, outfile);
                }
                else {
                        copy_tmpfile(tmpfile, stdout);
                }
        }
        else {
-               FILE *outfd = stdout;
+               outfile = stdout;
                if (outname) {
-                       outfd = fopen(outname, "w");
-                       if (outfd < 0) {
+                       outfile = fopen(outname, "w");
+                       if (!outfile) {
                                perror("error opening output file");
                                exit(1);
                        }
                }
                if (bufused)
-                       write_buff_out(bufstart, bufused, outfd);
-               fclose(outfd);
+                       write_buff_out(bufstart, bufused, outfile);
+               fclose(outfile);
        }
 
        return 0;