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ntfs: only alias volume $UpCase to default on exact match

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load_and_init_upcase() currently aliases vol->upcase to the global
default upcase whenever the shared prefix matches, and then truncates
vol->upcase_len to that shorter prefix.  The result is correct only by
accident: upcase[] accesses in name collation are gated by upcase_len,
so the prefix-equality alias produces the same fold output as keeping
the volume's own shorter table.

Still, prefix equality is not equality: the volume table is logically
distinct from the default and should not be replaced by it unless they
are byte-for-byte identical.  Use memcmp() to compare the complete table
in one expression and drop the now-redundant upcase_len rewrite.

No user-visible change is expected for compliant volumes whose $UpCase
has exactly default_upcase_len entries; shorter volume tables are no
longer aliased to the default.

Cc: stable@vger.kernel.org # v7.1
Signed-off-by: DaeMyung Kang <charsyam@gmail.com>
Reviewed-by: Hyunchul Lee <hyc.lee@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
This commit is contained in:
DaeMyung Kang 2026-05-21 19:17:51 +09:00 committed by Namjae Jeon
parent a9523a7d3b
commit 8f4b6e8bda
1 changed files with 3 additions and 9 deletions
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12
fs/ntfs/super.c
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@ -1323,7 +1323,6 @@ static bool load_and_init_upcase(struct ntfs_volume *vol)
u8 *addr;
pgoff_t index, max_index;
unsigned int size;
int i, max;
ntfs_debug("Entering.");
/* Read upcase table and setup vol->upcase and vol->upcase_len. */
@ -1374,16 +1373,11 @@ static bool load_and_init_upcase(struct ntfs_volume *vol)
mutex_unlock(&ntfs_lock);
return true;
}
max = default_upcase_len;
if (max > vol->upcase_len)
max = vol->upcase_len;
for (i = 0; i < max; i++)
if (vol->upcase[i] != default_upcase[i])
break;
if (i == max) {
if (default_upcase_len == vol->upcase_len &&
!memcmp(vol->upcase, default_upcase,
default_upcase_len * sizeof(*default_upcase))) {
kvfree(vol->upcase);
vol->upcase = default_upcase;
vol->upcase_len = max;
ntfs_nr_upcase_users++;
mutex_unlock(&ntfs_lock);
ntfs_debug("Volume specified $UpCase matches default. Using default.");