On Tue, Nov 01, 2022 at 10:33:12PM -0700, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@xxxxxxxxxx>
>
> Mounting a filesystem whose journal inode has the encrypt flag causes a
> NULL dereference in fscrypt_limit_io_blocks() when the 'inlinecrypt'
> mount option is used.
>
> The problem is that when jbd2_journal_init_inode() calls bmap(), it
> eventually finds its way into ext4_iomap_begin(), which calls
> fscrypt_limit_io_blocks(). fscrypt_limit_io_blocks() requires that if
> the inode is encrypted, then its encryption key must already be set up.
> That's not the case here, since the journal inode is never "opened" like
> a normal file would be. Hence the crash.
>
> A reproducer is:
>
> mkfs.ext4 -F /dev/vdb
> debugfs -w /dev/vdb -R "set_inode_field <8> flags 0x80808"
> mount /dev/vdb /mnt -o inlinecrypt
>
> To fix this, make ext4 consider journal inodes with the encrypt flag to
> be invalid. (Note, maybe other flags should be rejected on the journal
> inode too. For now, this is just the minimal fix for the above issue.)
>
> I've marked this as fixing the commit that introduced the call to
> fscrypt_limit_io_blocks(), since that's what made an actual crash start
> being possible. But this fix could be applied to any version of ext4
> that supports the encrypt feature.
>
> Reported-by: syzbot+ba9dac45bc76c490b7c3@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: 38ea50daa7a4 ("ext4: support direct I/O with fscrypt using blk-crypto")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
> ---
> fs/ext4/super.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 7950904fbf04f..2274f730b87e5 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -5723,7 +5723,7 @@ static struct inode *ext4_get_journal_inode(struct super_block *sb,
>
> ext4_debug("Journal inode found at %p: %lld bytes\n",
> journal_inode, journal_inode->i_size);
> - if (!S_ISREG(journal_inode->i_mode)) {
> + if (!S_ISREG(journal_inode->i_mode) || IS_ENCRYPTED(journal_inode)) {
> ext4_msg(sb, KERN_ERR, "invalid journal inode");
> iput(journal_inode);
> return NULL;
>
> base-commit: 8f71a2b3f435f29b787537d1abedaa7d8ebe6647
> --
Ping.
- Eric
