Per some comments from Lars Kellogg-Stedman <lars@larsshack.org>,

make xreadlink() return NULL on failure, and make sure everyone
uses the interface correctly.
 -Erik

7 files changed, 16 insertions, 11 deletions

diff --git a/applets/busybox.c b/applets/busybox.c
index badd53d79..41b6069ed 100644
--- a/applets/busybox.c
+++ b/applets/busybox.c
@@ -37,10 +37,7 @@ typedef int (*__link_f)(const char *, const char *);
  */
 static char *busybox_fullpath()
 {
-        char proc[256];
-
-        sprintf(proc, "/proc/%d/exe", getpid());
-        return xreadlink(proc);
+        return xreadlink("/proc/self/exe");
 }
 
 /* create (sym)links for each applet */
diff --git a/archival/tar.c b/archival/tar.c
index eb085c770..135bfd186 100644
--- a/archival/tar.c
+++ b/archival/tar.c
@@ -922,6 +922,8 @@ writeTarHeader(struct TarBallInfo *tbInfo, const char *header_name,
                 strncpy(header.linkname, tbInfo->hlInfo->name, sizeof(header.linkname));
         } else if (S_ISLNK(statbuf->st_mode)) {
                 char *lpath = xreadlink(real_name);
+                if (!lpath) /* Already printed err msg inside xreadlink() */
+                        return ( FALSE);
                 header.typeflag  = SYMTYPE;
                 strncpy(header.linkname, lpath, sizeof(header.linkname)); 
                 free(lpath);
diff --git a/busybox.c b/busybox.c
index badd53d79..41b6069ed 100644
--- a/busybox.c
+++ b/busybox.c
@@ -37,10 +37,7 @@ typedef int (*__link_f)(const char *, const char *);
  */
 static char *busybox_fullpath()
 {
-        char proc[256];
-
-        sprintf(proc, "/proc/%d/exe", getpid());
-        return xreadlink(proc);
+        return xreadlink("/proc/self/exe");
 }
 
 /* create (sym)links for each applet */
diff --git a/libbb/xreadlink.c b/libbb/xreadlink.c
index 66f63b883..932e487a5 100644
--- a/libbb/xreadlink.c
+++ b/libbb/xreadlink.c
@@ -1,5 +1,6 @@
 /*
- *  xreadlink.c - safe implementation of readlink
+ *  xreadlink.c - safe implementation of readlink.
+ *  Returns a NULL on failure...
  */
 
 #include <stdio.h>
@@ -22,8 +23,10 @@ extern char *xreadlink(const char *path)
         do {
                 buf = xrealloc(buf, bufsize += GROWBY);
                 readsize = readlink(path, buf, bufsize); /* 1st try */
-                if (readsize == -1)
-                        perror_msg("%s:%s", applet_name, path);
+                if (readsize == -1) {
+                    perror_msg("%s:%s", applet_name, path);
+                    return NULL;
+                }
         }           
         while (bufsize < readsize + 1);
 
diff --git a/miscutils/readlink.c b/miscutils/readlink.c
index 226649544..c46ebd108 100644
--- a/miscutils/readlink.c
+++ b/miscutils/readlink.c
@@ -37,6 +37,8 @@ int readlink_main(int argc, char **argv)
                 show_usage();
 
         buf = xreadlink(argv[1]);
+        if (!buf)
+                return EXIT_FAILURE;
         puts(buf);
 #ifdef BB_FEATURE_CLEAN_UP
         free(buf);
diff --git a/readlink.c b/readlink.c
index 226649544..c46ebd108 100644
--- a/readlink.c
+++ b/readlink.c
@@ -37,6 +37,8 @@ int readlink_main(int argc, char **argv)
                 show_usage();
 
         buf = xreadlink(argv[1]);
+        if (!buf)
+                return EXIT_FAILURE;
         puts(buf);
 #ifdef BB_FEATURE_CLEAN_UP
         free(buf);
diff --git a/tar.c b/tar.c
index eb085c770..135bfd186 100644
--- a/tar.c
+++ b/tar.c
@@ -922,6 +922,8 @@ writeTarHeader(struct TarBallInfo *tbInfo, const char *header_name,
                 strncpy(header.linkname, tbInfo->hlInfo->name, sizeof(header.linkname));
         } else if (S_ISLNK(statbuf->st_mode)) {
                 char *lpath = xreadlink(real_name);
+                if (!lpath) /* Already printed err msg inside xreadlink() */
+                        return ( FALSE);
                 header.typeflag  = SYMTYPE;
                 strncpy(header.linkname, lpath, sizeof(header.linkname)); 
                 free(lpath);