ex->ee_block is not host-endian (note that accesses of other fields
of *ex right next to that line go through the helpers that do proper
conversion from little-endian to host-endian; it might make sense
to add similar for ->ee_block to avoid reintroducing that kind of
bugs...)

Cc: stable@vger.kernel.org # v4.1+
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Fix multiple bugs in ext4_encrypted_zeroout(), including one that
could cause us to write an encrypted zero page to the wrong location
on disk, potentially causing data and file system corruption.
Fortunately, this tends to only show up in stress tests, but even with
these fixes, we are seeing some test failures with generic/127 --- but
these are now caused by data failures instead of metadata corruption.

Since ext4_encrypted_zeroout() is only used for some optimizations to
keep the extent tree from being too fragmented, and
ext4_encrypted_zeroout() itself isn't all that optimized from a time
or IOPS perspective, disable the extent tree optimization for
encrypted inodes for now.  This prevents the data corruption issues
reported by generic/127 until we can figure out what's going wrong.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org

Buggy (or hostile) userspace should not be able to cause the kernel to
crash.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org

Since ext4_page_crypto() doesn't need an encryption context (at least
not any more), this allows us to simplify a number function signature
and also allows us to avoid needing to allocate a context in
ext4_block_write_begin().  It also means we no longer need a separate
ext4_decrypt_one() function.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Previously we allocated bounce pages using a combination of
alloc_page() and mempool_alloc() with the __GFP_WAIT bit set.
Instead, use mempool_alloc() with GFP_NOWAIT.  The mempool_alloc()
function will try using alloc_pages() initially, and then only use the
mempool reserve of pages if alloc_pages() is unable to fulfill the
request.

This minimizes the the impact on the mm layer when we need to do a
large amount of writeback of encrypted files, as Jaeguk Kim had
reported that under a heavy fio workload on a system with restricted
amounts memory (which unfortunately, includes many mobile handsets),
he had observed the the OOM killer getting triggered several times.
Using GFP_NOWAIT

If the mempool_alloc() function fails, we will retry the page
writeback at a later time; the function of the mempool is to ensure
that we can writeback at least 32 pages at a time, so we can more
efficiently dispatch I/O under high memory pressure situations.  In
the future we should make this be a tunable so we can determine the
best tradeoff between permanently sequestering memory and the ability
to quickly launder pages so we can free up memory quickly when
necessary.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Fix up attempts by users to try to write to a file when they don't
have access to the encryption key.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>

ext4_encrypted_zeroout() could end up leaking a bio and bounce page.
Fortunately it's not used much.  While we're fixing things up,
refactor out common code into the static function alloc_bounce_page()
and fix up error handling if mempool_alloc() fails.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>

As suggested by Herbert Xu, we shouldn't allocate a new tfm each time
we read or write a page.  Instead we can use a single tfm hanging off
the inode's crypt_info structure for all of our encryption needs for
that inode, since the tfm can be used by multiple crypto requests in
parallel.

Also use cmpxchg() to avoid races that could result in crypt_info
structure getting doubly allocated or doubly freed.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Some fields are only used when the crypto_ctx is being used on the
read path, some are only used on the write path, and some are only
used when the structure is on free list.  Optimize memory use by using
a union.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>