Don't just loop indefinitely when an obfuscated name comes up as a
duplicate. Count the number of times we've found a duplicate and if
if it gets excessive despite choosing names at random, just give up
and use the original name without obfuscation.
Technically, a typical 5-character name has 255 other names that can
have the same hash value. But the algorithm doesn't hit all
possible names (far from it) so duplicates are still possible.
Signed-off-by: Alex Elder <aelder@xxxxxxx>
Reviewed-by: Dave Chinner <dchinner@xxxxxxxxxx>
Updates (v4):
- Rearranged things a bit so that if too many duplicates are
encountered, a warning gets emitted.
Dave already signed off on it but the update was different enough I
thought I should post it once more.
---
db/metadump.c | 42 +++++++++++++++++++++++++++++++-----------
1 file changed, 31 insertions(+), 11 deletions(-)
Index: b/db/metadump.c
===================================================================
--- a/db/metadump.c
+++ b/db/metadump.c
@@ -29,6 +29,14 @@
#define DEFAULT_MAX_EXT_SIZE 1000
+/*
+ * It's possible that multiple files in a directory (or attributes
+ * in a file) produce the same obfuscated name. If that happens, we
+ * try to create another one. After several rounds of this though,
+ * we just give up and leave the original name as-is.
+ */
+#define DUP_MAX 5 /* Max duplicates before we give up */
+
/* copy all metadata structures to/from a file */
static int metadump_f(int argc, char **argv);
@@ -444,8 +452,9 @@ generate_obfuscated_name(
{
xfs_dahash_t hash;
name_ent_t *p;
- int dup;
+ int dup = 0;
uchar_t newname[NAME_MAX];
+ uchar_t *newp;
/*
* Our obfuscation algorithm requires at least 5-character
@@ -481,19 +490,17 @@ generate_obfuscated_name(
do {
int i;
xfs_dahash_t newhash = 0;
- uchar_t *newp = &newname[0];
uchar_t *first;
uchar_t high_bit;
int shift;
- dup = 0;
-
/*
* The beginning of the obfuscated name can be
* pretty much anything, so fill it in with random
* characters. Accumulate its new hash value as we
* go.
*/
+ newp = &newname[0];
for (i = 0; i < namelen - 5; i++) {
*newp = random_filename_char();
newhash = *newp ^ rol32(newhash, 7);
@@ -541,14 +548,31 @@ generate_obfuscated_name(
ASSERT(libxfs_da_hashname(newname, namelen) == hash);
+ /*
+ * Search the name table to be sure we don't produce
+ * a name that's already been used.
+ */
for (p = nametable[hash % NAME_TABLE_SIZE]; p; p = p->next) {
if (p->hash == hash && p->namelen == namelen &&
!memcmp(p->name, newname, namelen)) {
- dup = 1;
+ dup++;
break;
}
}
- } while (dup);
+ } while (dup && dup < DUP_MAX);
+
+ /*
+ * Update the caller's copy with the obfuscated name. Use
+ * the original name if we got too many duplicates--and if
+ * so, issue a warning.
+ */
+ if (dup < DUP_MAX)
+ memcpy(name, newname, namelen);
+ else
+ print_warning("duplicate name for inode %llu "
+ "in dir inode %llu\n",
+ (unsigned long long) ino,
+ (unsigned long long) cur_ino);
/* Create an entry for the name in the name table */
@@ -557,15 +581,11 @@ generate_obfuscated_name(
return;
p->namelen = namelen;
- memcpy(p->name, newname, namelen);
+ memcpy(p->name, name, namelen);
p->hash = hash;
p->next = nametable[hash % NAME_TABLE_SIZE];
nametable[hash % NAME_TABLE_SIZE] = p;
-
- /* Update the caller's copy with the obfuscated name */
-
- memcpy(name, newname, namelen);
}
static void
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