[PATCH 0/5] Be careful about lstat()-vs-readlink()

[Linus Torvalds <torvalds@linux-foundation.org>]

This series of five patches makes us a lot more careful about readlink(), 
and in particular it avoids the code that depends on doing an lstat(), and 
then using st_size as the length of the link. That's what POSIX says 
_should_ happen, but Ramon Tayag reported git failing on NTFS under Linux 
because st_size doesn't match readlink() return value.

It doesn't seem to be unknown elsewhere either, since coreutils (through 
gnulib's areadlink_with_size) also has a big compatibility layer around 
readlink().

This series has been 'tested' by running it with the appended totally 
hacky patch that fakes out the lstat() st_size values for symlinks, so it 
has actually had some testing. 

The complete series does:

Linus Torvalds (5):
  Add generic 'strbuf_readlink()' helper function
  Make 'ce_compare_link()' use the new 'strbuf_readlink()'
  Make 'index_path()' use 'strbuf_readlink()'
  Make 'diff_populate_filespec()' use the new 'strbuf_readlink()'
  Make 'prepare_temp_file()' ignore st_size for symlinks

 builtin-apply.c |    6 ++----
 diff.c          |   25 +++++++++++--------------
 read-cache.c    |   22 ++++++++--------------
 sha1_file.c     |   14 +++++---------
 strbuf.c        |   28 ++++++++++++++++++++++++++++
 strbuf.h        |    1 +
 6 files changed, 55 insertions(+), 41 deletions(-)

and the hacky test-patch (which is obviously _not_ meant to be applied) is 
as follows...

		Linus

---
diff --git a/cache.h b/cache.h
index 231c06d..2d85fca 100644
--- a/cache.h
+++ b/cache.h
@@ -943,4 +943,7 @@ void overlay_tree_on_cache(const char *tree_name, const char *prefix);
 char *alias_lookup(const char *alias);
 int split_cmdline(char *cmdline, const char ***argv);
 
+extern int gitlstat(const char *, struct stat *);
+#define lstat gitlstat
+
 #endif /* CACHE_H */
diff --git a/read-cache.c b/read-cache.c
index b1475ff..defbb20 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -15,6 +15,16 @@
 #include "revision.h"
 #include "blob.h"
 
+#undef lstat
+int gitlstat(const char *path, struct stat *buf)
+{
+	int retval = lstat(path, buf);
+	if (!retval && S_ISLNK(buf->st_mode))
+		buf->st_size = 1;
+	return retval;
+}
+#define lstat gitlstat
+
 /* Index extensions.
  *
  * The first letter should be 'A'..'Z' for extensions that are not