linux-kernel - [PATCH 5.4 05/56] fs-verity: fix signed integer overflow with i_size near S64

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Message-Id: <20211004125030.183851324@linuxfoundation.org>
Date:   Mon,  4 Oct 2021 14:52:25 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Boris Burkov <boris@....io>,
        Eric Biggers <ebiggers@...gle.com>
Subject: [PATCH 5.4 05/56] fs-verity: fix signed integer overflow with i_size near S64_MAX

From: Eric Biggers <ebiggers@...gle.com>

commit 80f6e3080bfcf865062a926817b3ca6c4a137a57 upstream.

If the file size is almost S64_MAX, the calculated number of Merkle tree
levels exceeds FS_VERITY_MAX_LEVELS, causing FS_IOC_ENABLE_VERITY to
fail.  This is unintentional, since as the comment above the definition
of FS_VERITY_MAX_LEVELS states, it is enough for over U64_MAX bytes of
data using SHA-256 and 4K blocks.  (Specifically, 4096*128**8 >= 2**64.)

The bug is actually that when the number of blocks in the first level is
calculated from i_size, there is a signed integer overflow due to i_size
being signed.  Fix this by treating i_size as unsigned.

This was found by the new test "generic: test fs-verity EFBIG scenarios"
(https://lkml.kernel.org/r/b1d116cd4d0ea74b9cd86f349c672021e005a75c.1631558495.git.boris@bur.io).

This didn't affect ext4 or f2fs since those have a smaller maximum file
size, but it did affect btrfs which allows files up to S64_MAX bytes.

Reported-by: Boris Burkov <boris@....io>
Fixes: 3fda4c617e84 ("fs-verity: implement FS_IOC_ENABLE_VERITY ioctl")
Fixes: fd2d1acfcadf ("fs-verity: add the hook for file ->open()")
Cc: <stable@...r.kernel.org> # v5.4+
Reviewed-by: Boris Burkov <boris@....io>
Link: https://lore.kernel.org/r/20210916203424.113376-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@...gle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/verity/enable.c |    2 +-
 fs/verity/open.c   |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

--- a/fs/verity/enable.c
+++ b/fs/verity/enable.c
@@ -136,7 +136,7 @@ static int build_merkle_tree(struct inod
 	 * (level 0) and ascending to the root node (level 'num_levels - 1').
 	 * Then at the end (level 'num_levels'), calculate the root hash.
 	 */
-	blocks = (inode->i_size + params->block_size - 1) >>
+	blocks = ((u64)inode->i_size + params->block_size - 1) >>
 		 params->log_blocksize;
 	for (level = 0; level <= params->num_levels; level++) {
 		err = build_merkle_tree_level(inode, level, blocks, params,
--- a/fs/verity/open.c
+++ b/fs/verity/open.c
@@ -89,7 +89,7 @@ int fsverity_init_merkle_tree_params(str
 	 */
 
 	/* Compute number of levels and the number of blocks in each level */
-	blocks = (inode->i_size + params->block_size - 1) >> log_blocksize;
+	blocks = ((u64)inode->i_size + params->block_size - 1) >> log_blocksize;
 	pr_debug("Data is %lld bytes (%llu blocks)\n", inode->i_size, blocks);
 	while (blocks > 1) {
 		if (params->num_levels >= FS_VERITY_MAX_LEVELS) {