add a 'mangle prefix' option to allow people to tune the number of

characters used in the prefix for 8.3 names in the hash2
algorithm. The longer the prefix the more readable the 8.3 names will
be, but the weaker the hash.

this was added because of someone complaining that the new hashing
algorithm was unreadable but the old one was broken :)
(This used to be commit 3ca3cc838e5b957c7244b21947daddc4ee4c3099)

1 files changed, 41 insertions, 16 deletions

diff --git a/source3/smbd/mangle_hash2.c b/source3/smbd/mangle_hash2.c
index 5adde19eea..bbc9020eab 100644
--- a/source3/smbd/mangle_hash2.c
+++ b/source3/smbd/mangle_hash2.c
@@ -87,6 +87,13 @@ static unsigned char char_flags[256];
 
 #define FLAG_CHECK(c, flag) (char_flags[(unsigned char)(c)] & (flag))
 
+/*
+  this determines how many characters are used from the original filename
+  in the 8.3 mangled name. A larger value leads to a weaker hash and more collisions.
+  The largest possible value is 6.
+*/
+static unsigned mangle_prefix;
+
 /* we will use a very simple direct mapped prefix cache. The big
    advantage of this cache structure is speed and low memory usage 
 
@@ -217,16 +224,18 @@ static BOOL is_mangled_component(const char *name)
 		}
 	}
 	
-	/* check first character */
-	if (! FLAG_CHECK(name[0], FLAG_ASCII)) {
-		return False;
+	/* check lead characters */
+	for (i=0;i<mangle_prefix;i++) {
+		if (! FLAG_CHECK(name[i], FLAG_ASCII)) {
+			return False;
+		}
 	}
 	
 	/* check rest of hash */
 	if (! FLAG_CHECK(name[7], FLAG_BASECHAR)) {
 		return False;
 	}
-	for (i=1;i<6;i++) {
+	for (i=mangle_prefix;i<6;i++) {
 		if (! FLAG_CHECK(name[i], FLAG_BASECHAR)) {
 			return False;
 		}
@@ -371,7 +380,7 @@ static BOOL check_cache(char *name)
 
 	/* we need to extract the hash from the 8.3 name */
 	hash = base_reverse[(unsigned char)name[7]];
-	for (multiplier=36, i=5;i>=1;i--) {
+	for (multiplier=36, i=5;i>=mangle_prefix;i--) {
 		u32 v = base_reverse[(unsigned char)name[i]];
 		hash += multiplier * v;
 		multiplier *= 36;
@@ -478,7 +487,7 @@ static BOOL is_legal_name(const char *name)
 static void name_map(char *name, BOOL need83, BOOL cache83)
 {
 	char *dot_p;
-	char lead_char;
+	char lead_chars[7];
 	char extension[4];
 	int extension_length, i;
 	int prefix_len;
@@ -516,15 +525,20 @@ static void name_map(char *name, BOOL need83, BOOL cache83)
 		if (i == 0 || i == 4) dot_p = NULL;
 	}
 
-	/* the leading character in the mangled name is taken from
-	   the first character of the name, if it is ascii 
-	   otherwise '_' is used
+	/* the leading characters in the mangled name is taken from
+	   the first characters of the name, if they are ascii otherwise
+	   '_' is used
 	*/
-	lead_char = name[0];
-	if (! FLAG_CHECK(lead_char, FLAG_ASCII)) {
-		lead_char = '_';
+	for (i=0;i<mangle_prefix && name[i];i++) {
+		lead_chars[i] = name[i];
+		if (! FLAG_CHECK(lead_chars[i], FLAG_ASCII)) {
+			lead_chars[i] = '_';
+		}
+		lead_chars[i] = toupper(lead_chars[i]);
+	}
+	for (;i<mangle_prefix;i++) {
+		lead_chars[i] = '_';
 	}
-	lead_char = toupper(lead_char);
 
 	/* the prefix is anything up to the first dot */
 	if (dot_p) {
@@ -549,10 +563,12 @@ static void name_map(char *name, BOOL need83, BOOL cache83)
 	v = hash = mangle_hash(name, prefix_len);
 
 	/* now form the mangled name. */
-	new_name[0] = lead_char;
+	for (i=0;i<mangle_prefix;i++) {
+		new_name[i] = lead_chars[i];
+	}
 	new_name[7] = base_forward(v % 36);
 	new_name[6] = '~';	
-	for (i=5; i>=1; i--) {
+	for (i=5; i>=mangle_prefix; i--) {
 		v = v / 36;
 		new_name[i] = base_forward(v % 36);
 	}
@@ -594,7 +610,7 @@ static void init_tables(void)
 
 	memset(char_flags, 0, sizeof(char_flags));
 
-	for (i=0;i<128;i++) {
+	for (i=1;i<128;i++) {
 		if ((i >= '0' && i <= '9') || 
 		    (i >= 'a' && i <= 'z') || 
 		    (i >= 'A' && i <= 'Z')) {
@@ -656,6 +672,15 @@ static struct mangle_fns mangle_fns = {
 /* return the methods for this mangling implementation */
 struct mangle_fns *mangle_hash2_init(void)
 {
+	/* the mangle prefix can only be in the mange 1 to 6 */
+	mangle_prefix = lp_mangle_prefix();
+	if (mangle_prefix > 6) {
+		mangle_prefix = 6;
+	}
+	if (mangle_prefix < 1) {
+		mangle_prefix = 1;
+	}
+
 	init_tables();
 	mangle_reset();