Whoops, apparently stat::st_size isn't set to the string length of a …

…symlink's linkdest, so we were misallocating buffers here for the readlink(). With that in mind, I made an platform layer abstraction for readlink() and made the unix one robust to handle when we don't know the linkdest's size (er...which is always, but readlink() isn't real helpful here either).
icculus · Jul 2, 2007 · 504d310 · 504d310
1 parent d8bf02c
commit 504d310
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Showing 3 changed files with 33 additions and 12 deletions.
diff --git a/fileio.c b/fileio.c
@@ -6,7 +6,6 @@
  *  This file written by Ryan C. Gordon.
  */
 
-#include <unistd.h>  // !!! FIXME: unix dependency for readlink().
 #include <sys/stat.h>  // !!! FIXME: unix dependency for stat().
 
 #include "fileio.h"
@@ -415,13 +414,12 @@ static const MojoArchiveEntry *MojoArchive_dir_enumNext(MojoArchive *ar)
         else if (S_ISLNK(statbuf.st_mode))
         {
             ar->prevEnum.type = MOJOARCHIVE_ENTRY_SYMLINK;
-            ar->prevEnum.linkdest = (char *) xmalloc(statbuf.st_size + 1);
-            if (readlink(fullpath, ar->prevEnum.linkdest, statbuf.st_size) < 0)
+            ar->prevEnum.linkdest = MojoPlatform_readlink(fullpath);
+            if (ar->prevEnum.linkdest == NULL)
             {
                 free(fullpath);
                 return MojoArchive_dir_enumNext(ar);
             } // if
-            ar->prevEnum.linkdest[statbuf.st_size] = '\0';
         } // else if
 
         else if (S_ISDIR(statbuf.st_mode))

diff --git a/platform.h b/platform.h
@@ -49,6 +49,11 @@ char *MojoPlatform_realpath(const char *path);
 //  syscall! Returns true if link was created, false otherwise.
 boolean MojoPlatform_symlink(const char *src, const char *dst);
 
+// Read the destination from symlink (linkname). Returns a pointer
+//  allocated with xmalloc() containing the linkdest on success, and NULL
+//  on failure. The caller is responsible for freeing the returned pointer!
+char *MojoPlatform_readlink(const char *linkname);
+
 // !!! FIXME: comment me.
 boolean MojoPlatform_mkdir(const char *path, uint16 perms);
 

diff --git a/platform_unix.c b/platform_unix.c
@@ -82,6 +82,29 @@ char *MojoPlatform_currentWorkingDir(void)
 } // MojoPlatform_currentWorkingDir
 
 
+char *MojoPlatform_readlink(const char *linkname)
+{
+    size_t alloclen = 16;
+    char *retval = NULL;
+    char *buf = NULL;
+    size_t len = -1;
+
+    do
+    {
+        alloclen *= 2;
+        buf = xrealloc(buf, alloclen);
+        len = readlink(linkname, buf, alloclen-1);
+        if ( (len != -1) && (len < (alloclen-1)) )  // !error && !overflow
+        {
+            buf[len] = '\0';  // readlink() doesn't null-terminate!
+            retval = xrealloc(buf, len+1);  // shrink it down.
+        } // if
+    } while (len >= (alloclen-1));  // loop if we need a bigger buffer.
+
+    return retval;  // caller must free() this.
+} // MojoPlatform_readlink
+
+
 static void *guaranteeAllocation(void *ptr, size_t len, size_t *_alloclen)
 {
     void *retval = NULL;
@@ -176,19 +199,13 @@ static char *realpathInternal(char *path, const char *cwd, int linkloop)
         else if (S_ISLNK(statbuf.st_mode))
         {
             char *newresolve = NULL;
-            int br = 0;
-
             if (linkloop > 255)
                 goto realpathInternal_failed;
 
-            linkname = (char *) xmalloc(statbuf.st_size + 1);
-            br = readlink(retval, linkname, statbuf.st_size);
-            if (br < 0)
+            linkname = MojoPlatform_readlink(retval);
+            if (linkname == NULL)
                 goto realpathInternal_failed;
 
-            // readlink() doesn't null-terminate!
-            linkname[br] = '\0';
-
             // chop off symlink name for its cwd.
             retval[len] = '\0';
 
@@ -202,6 +219,7 @@ static char *realpathInternal(char *path, const char *cwd, int linkloop)
             strcpy(retval, newresolve);
             free(newresolve);
             free(linkname);
+            linkname = NULL;
         } // else if
 
         else