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fs-verity: fix signed integer overflow with i_size near S64_MAX

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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@bur.io>
Fixes: 3fda4c617e ("fs-verity: implement FS_IOC_ENABLE_VERITY ioctl")
Fixes: fd2d1acfca ("fs-verity: add the hook for file ->open()")
Cc: <stable@vger.kernel.org> # v5.4+
Reviewed-by: Boris Burkov <boris@bur.io>
Link: https://lore.kernel.org/r/20210916203424.113376-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
This commit is contained in:
Eric Biggers 2021-09-16 13:34:24 -07:00
parent e4e737bb5c
commit 80f6e3080b
2 changed files with 2 additions and 2 deletions
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2
fs/verity/enable.c
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@ -177,7 +177,7 @@ static int build_merkle_tree(struct file *filp,
* (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(filp, level, blocks, params,

2
fs/verity/open.c
View File

@ -89,7 +89,7 @@ int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
*/
/* 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) {