[PATCH v2 17/20] btrfs: reuse encrypted filename hash when possible.

Sweet Tea Dorminy
2022-09-06T00:36:19Z

From: Omar Sandoval <osandov@osandov.com>

For encrypted fscrypt_names, we can reuse fscrypt's precomputed hash of
the encrypted name to generate our own hash, instead of rehashing the
unencrypted name (which may not be possible if it's a nokey name).

Signed-off-by: Omar Sandoval <osandov@osandov.com>
Signed-off-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
---
fs/btrfs/ctree.h | 21 ++++++++++++++++++---
1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index e8d000fcc85d..aa599518c057 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -2842,7 +2842,10 @@ static inline void btrfs_crc32c_final(u32 crc, u8 *result)

static inline u64 btrfs_name_hash(const struct fscrypt_name *name)
{
- return crc32c((u32)~1, fname_name(name), fname_len(name));
+ if (fname_name(name))
+ return crc32c((u32)~1, fname_name(name), fname_len(name));
+ else
+ return name->hash | ((u64)name->minor_hash << 32);
}

/*
@@ -2851,8 +2854,20 @@ static inline u64 btrfs_name_hash(const struct fscrypt_name *name)
static inline u64 btrfs_extref_hash(u64 parent_objectid,
const struct fscrypt_name *name)
{
- return (u64) crc32c(parent_objectid, fname_name(name),
- fname_len(name));
+ /*
+ * If the name is encrypted and we don't have the key, we can use the
+ * fscrypt-provided hash instead of the normal name, and do the steps
+ * of crc32c() manually. Else, just hash the name, parent objectid,
+ * and name length.
+ */
+ if (fname_name(name))
+ return (u64) crc32c(parent_objectid, fname_name(name),
+ fname_len(name));
+ else
+ return (__crc32c_le_combine(parent_objectid,
+ name->hash,
+ fname_len(name)) ^
+ __crc32c_le_shift(~1, fname_len(name)));
}

static inline gfp_t btrfs_alloc_write_mask(struct address_space *mapping)
--
2.35.1