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fscrypt_initialize(), which allocates the global bounce page pool when
an encrypted file is first accessed, uses "double-checked locking" to
try to avoid locking fscrypt_init_mutex. However, it doesn't use any
memory barriers, so it's theoretically possible for a thread to observe
a bounce page pool which has not been fully initialized. This is a
classic bug with "double-checked locking".
While "only a theoretical issue" in the latest kernel, in pre-4.8
kernels the pointer that was checked was not even the last to be
initialized, so it was easily possible for a crash (NULL pointer
dereference) to happen. This was changed only incidentally by the large
refactor to use fs/crypto/.
Solve both problems in a trivial way that can easily be backported: just
always take the mutex. It's theoretically less efficient, but it
shouldn't be noticeable in practice as the mutex is only acquired very
briefly once per encrypted file.
Later I'd like to make this use a helper macro like DO_ONCE(). However,
DO_ONCE() runs in atomic context, so we'd need to add a new macro that
allows blocking.
Cc: stable@vger.kernel.org # v4.1+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
(cherry-picked from commit a0b3bc855374c50b5ea85273553485af48caf2f7
and fixed up for android-3.18)
Change-Id: I18c7231af7de2319883934d2e36ea54e1eb44466
Signed-off-by: Eric Biggers <ebiggers@google.com>
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Cc: stable@kernel.org
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: "Theodore Ts'o" <tytso@google.com>
Change-Id: Ia13629b6512a0c5dd2a09e7e3676c74af20c96a3
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Return value of ext4_derive_key_aes() is stored but not used.
Add test to exit cleanly if ext4_derive_key_aes() fail.
Also fix coverity CID 1309760.
Signed-off-by: Laurent Navet <laurent.navet@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: "Theodore Ts'o" <tytso@google.com>
Change-Id: I796cdfc65386e546f332a3dbbf9f2c2cd76e3301
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Buggy (or hostile) userspace should not be able to cause the kernel to
crash.
Change-Id: I67f7b32dd458d577b506ddff6ef07955e804e3ff
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: "Theodore Ts'o" <tytso@google.com>
Cc: stable@vger.kernel.org
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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.
Change-Id: I4ae5c07d0e5d99ec1e26eeb49d833c4a284d9a5f
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Theodore Ts'o <tytso@google.com>
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The ci_mode field was superfluous, and getting rid of it gets rid of
an unused hole in the structure.
Change-Id: I0f4c38a1162fa9c6da8a3529b7477ff5560c21df
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: "Theodore Ts'o" <tytso@google.com>
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Use slab caches the ext4_crypto_ctx and ext4_crypt_info structures for
slighly better memory efficiency and debuggability.
Change-Id: If47986e2e29fa181d113864dcd9d1cae79c72639
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: "Theodore Ts'o" <tytso@google.com>
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This is a pretty massive patch which does a number of different things:
1) The per-inode encryption information is now stored in an allocated
data structure, ext4_crypt_info, instead of directly in the node.
This reduces the size usage of an in-memory inode when it is not
using encryption.
2) We drop the ext4_fname_crypto_ctx entirely, and use the per-inode
encryption structure instead. This remove an unnecessary memory
allocation and free for the fname_crypto_ctx as well as allowing us
to reuse the ctfm in a directory for multiple lookups and file
creations.
3) We also cache the inode's policy information in the ext4_crypt_info
structure so we don't have to continually read it out of the
extended attributes.
4) We now keep the keyring key in the inode's encryption structure
instead of releasing it after we are done using it to derive the
per-inode key. This allows us to test to see if the key has been
revoked; if it has, we prevent the use of the derived key and free
it.
5) When an inode is released (or when the derived key is freed), we
will use memset_explicit() to zero out the derived key, so it's not
left hanging around in memory. This implies that when a user logs
out, it is important to first revoke the key, and then unlink it,
and then finally, to use "echo 3 > /proc/sys/vm/drop_caches" to
release any decrypted pages and dcache entries from the system
caches.
6) All this, and we also shrink the number of lines of code by around
100. :-)
Change-Id: I948f7844d425c0ce616f800446ecb0b6bea686f8
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Theodore Ts'o <tytso@google.com>
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Use struct ext4_encryption_key only for the master key passed via the
kernel keyring.
For internal kernel space users, we now use struct ext4_crypt_info.
This will allow us to put information from the policy structure so we
can cache it and avoid needing to constantly looking up the extended
attribute. We will do this in a spearate patch. This patch is mostly
mechnical to make it easier for patch review.
Change-Id: I208472675d0550df5f60b3b58652a9a1b434caed
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Theodore Ts'o <tytso@google.com>
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This obscures the length of the filenames, to decrease the amount of
information leakage. By default, we pad the filenames to the next 4
byte boundaries. This costs nothing, since the directory entries are
aligned to 4 byte boundaries anyway. Filenames can also be padded to
8, 16, or 32 bytes, which will consume more directory space.
Change-Id: I2d4ab2b76797ab93fada683f405e3876e0cff9dc
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Theodore Ts'o <tytso@google.com>
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Also add the test dummy encryption mode flag so we can more easily
test the encryption patches using xfstests.
Change-Id: Iaae44110ab5870e5da60aca76197828f0ebc139b
Signed-off-by: Michael Halcrow <mhalcrow@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Theodore Ts'o <tytso@google.com>
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Change-Id: I4e59c73febff7041c9db6c58c775413e2f5bd0e8
Signed-off-by: Michael Halcrow <mhalcrow@google.com>
Signed-off-by: Ildar Muslukhov <muslukhovi@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Theodore Ts'o <tytso@google.com>
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