index: be careful when handling long names

We currently use lower 12-bit (masked with CE_NAMEMASK) in the
ce_flags field to store the length of the name in cache_entry,
without checking the length parameter given to
create_ce_flags().  This can make us store incorrect length.

Currently we are mostly protected by the fact that many
codepaths first copy the path in a variable of size PATH_MAX,
which typically is 4096 that happens to match the limit, but
that feels like a bug waiting to happen.  Besides, that would
not allow us to shorten the width of CE_NAMEMASK to use the bits
for new flags.

This redefines the meaning of the name length stored in the
cache_entry.  A name that does not fit is represented by storing
CE_NAMEMASK in the field, and the actual length needs to be
computed by actually counting the bytes in the name[] field.
This way, only the unusually long paths need to suffer.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 15 insertions, 2 deletions

diff --git a/cache.h b/cache.h
index 4a054c540..9eaffdefd 100644
--- a/cache.h
+++ b/cache.h
@@ -131,8 +131,21 @@ struct cache_entry {
 #define CE_UPDATE    (0x10000)
 #define CE_REMOVE    (0x20000)
 
-#define create_ce_flags(len, stage) ((len) | ((stage) << CE_STAGESHIFT))
-#define ce_namelen(ce) (CE_NAMEMASK & (ce)->ce_flags)
+static inline unsigned create_ce_flags(size_t len, unsigned stage)
+{
+	if (len >= CE_NAMEMASK)
+		len = CE_NAMEMASK;
+	return (len | (stage << CE_STAGESHIFT));
+}
+
+static inline size_t ce_namelen(const struct cache_entry *ce)
+{
+	size_t len = ce->ce_flags & CE_NAMEMASK;
+	if (len < CE_NAMEMASK)
+		return len;
+	return strlen(ce->name + CE_NAMEMASK) + CE_NAMEMASK;
+}
+
 #define ce_size(ce) cache_entry_size(ce_namelen(ce))
 #define ondisk_ce_size(ce) ondisk_cache_entry_size(ce_namelen(ce))
 #define ce_stage(ce) ((CE_STAGEMASK & (ce)->ce_flags) >> CE_STAGESHIFT)