[PATCH v2 01/11] fsverity: use unsigned long for level_start

Eric Biggers
2022-12-23T20:37:00Z

From: Eric Biggers <ebiggers@google.com>

fs/verity/ isn't consistent with whether Merkle tree block indices are
'unsigned long' or 'u64'. There's no real point to using u64 for them,
though, since (a) a Merkle tree with over ULONG_MAX blocks would only be
needed for a file larger than MAX_LFS_FILESIZE, and (b) for reads, the
status of all Merkle tree blocks has to be tracked in memory.

Therefore, let's make things a bit more efficient on 32-bit systems by
using 'unsigned long[]' for merkle_tree_params::level_start, instead of
'u64[]'. Also, to be extra safe, explicitly check that there aren't
more than ULONG_MAX Merkle tree blocks.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
fs/verity/fsverity_private.h | 2 +-
fs/verity/open.c | 20 +++++++++++++++-----
2 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/fs/verity/fsverity_private.h b/fs/verity/fsverity_private.h
index a16038a0ee67d..e8b40c8000be7 100644
--- a/fs/verity/fsverity_private.h
+++ b/fs/verity/fsverity_private.h
@@ -52,7 +52,7 @@ struct merkle_tree_params {
* Starting block index for each tree level, ordered from leaf level (0)
* to root level ('num_levels - 1')
*/
- u64 level_start[FS_VERITY_MAX_LEVELS];
+ unsigned long level_start[FS_VERITY_MAX_LEVELS];
};

/*
diff --git a/fs/verity/open.c b/fs/verity/open.c
index e0ef1a6283943..83ccc3c137363 100644
--- a/fs/verity/open.c
+++ b/fs/verity/open.c
@@ -34,6 +34,7 @@ int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
struct fsverity_hash_alg *hash_alg;
int err;
u64 blocks;
+ u64 blocks_in_level[FS_VERITY_MAX_LEVELS];
u64 offset;
int level;

@@ -94,17 +95,26 @@ int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
}
blocks = (blocks + params->hashes_per_block - 1) >>
params->log_arity;
- /* temporarily using level_start[] to store blocks in level */
- params->level_start[params->num_levels++] = blocks;
+ blocks_in_level[params->num_levels++] = blocks;
}
- params->level0_blocks = params->level_start[0];
+ params->level0_blocks = blocks_in_level[0];

/* Compute the starting block of each level */
offset = 0;
for (level = (int)params->num_levels - 1; level >= 0; level--) {
- blocks = params->level_start[level];
params->level_start[level] = offset;
- offset += blocks;
+ offset += blocks_in_level[level];
+ }
+
+ /*
+ * Since the data, and thus also the Merkle tree, cannot have more than
+ * ULONG_MAX pages, hash block indices can always fit in an
+ * 'unsigned long'. To be safe, explicitly check for it too.
+ */
+ if (offset > ULONG_MAX) {
+ fsverity_err(inode, "Too many blocks in Merkle tree");
+ err = -EFBIG;
+ goto out_err;
}

params->tree_size = offset << log_blocksize;
--
2.39.0