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Message-ID: <20171008191749.GA26458@zzz.localdomain> Date: Sun, 8 Oct 2017 12:17:49 -0700 From: Eric Biggers <ebiggers3@...il.com> To: Theodore Ts'o <tytso@....edu> Cc: stable@...r.kernel.org, linux-ext4@...r.kernel.org Subject: Re: [FOR STABLE 4.1] ext4 crypto: don't regenerate the per-inode encryption key unnecessarily Hi Ted, On Sun, Oct 08, 2017 at 02:09:53PM -0400, Theodore Ts'o wrote: > diff --git a/fs/ext4/crypto_key.c b/fs/ext4/crypto_key.c > index 52170d0b7c40..c8c3bf0286be 100644 > --- a/fs/ext4/crypto_key.c > +++ b/fs/ext4/crypto_key.c > @@ -99,9 +99,14 @@ int ext4_generate_encryption_key(struct inode *inode) > struct ext4_encryption_context ctx; > struct user_key_payload *ukp; > struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb); > - int res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION, > - EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, > - &ctx, sizeof(ctx)); > + int res; > + > + if (ext4_has_encryption_key(inode)) > + return 0; > + > + res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION, > + EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, > + &ctx, sizeof(ctx)); > > if (res != sizeof(ctx)) { > if (res > 0) This is an improvement, but it's still broken because there is no locking. If two processes ->open() the same inode at the same time, one can observe ext4_has_encryption_key() as true before the key has been fully initialized. It may be a good idea to add a really simple DEFINE_MUTEX(ext4_key_generation_mutex), then do the ext4_has_encryption_key() check and key generation under the mutex... Eric
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