From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Chandan Rajendra Subject: [PATCH V5 1/7] buffer_head: Introduce BH_Read_Cb flag Date: Fri, 23 Aug 2019 18:55:36 +0530 Message-Id: <20190823132542.13434-2-chandan@linux.ibm.com> In-Reply-To: <20190823132542.13434-1-chandan@linux.ibm.com> References: <20190823132542.13434-1-chandan@linux.ibm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit To: linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-fscrypt@vger.kernel.org Cc: Chandan Rajendra , tytso@mit.edu, adilger.kernel@dilger.ca, ebiggers@kernel.org, hch@infradead.org, chandanrlinux@gmail.com List-ID: Decryption of file content encrypted using fscrypt relies on bio->bi_private holding a pointer to an encryption context i.e. Decryption operation is not performed for bios having a NULL value at bio->bi_private. The same logic cannot be used on buffer heads because, 1. In Btrfs, write_dev_supers() sets bh->b_private to 'struct btrfs_device' pointer and submits the buffer head for a write operation. 1. In btrfs/146 test, the write operation fails and hence the endio function clears the BH_Uptodate flag. 2. A read operation initiated later will submit the buffer head to the block layer. During endio processing, bh_>b_private would have a non-NULL value. 2. Another instance is when an Ext4 metadata block with BH_Uptodate set and also part of the in-memory JBD list undergoes the following, 1. A sync() syscall is invoked by the userspace and the write operation on the metadata block is initiated. 2. Due to an I/O failure, the BH_Uptodate flag is cleared by end_buffer_async_write(). The bh->b_private member would be pointing to a journal head structure. 3. In such a case, a read operation invoked on the block mapped by the buffer head will initiate a read from the disk since the buffer head is missing the BH_Uptodate flag. 4. After the read I/O request is submitted, end_buffer_async_read() will find a non-NULL value at bh->b_private. This scenario was observed when executing generic/475 test case. Hence this commit introduces a new buffer head flag to reliably check for decryption of a buffer head's contents after the block has been read from the disk. Signed-off-by: Chandan Rajendra --- include/linux/buffer_head.h | 2 ++ 1 file changed, 2 insertions(+) diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h index 7b73ef7f902d..08f217ba8114 100644 --- a/include/linux/buffer_head.h +++ b/include/linux/buffer_head.h @@ -38,6 +38,7 @@ enum bh_state_bits { BH_Meta, /* Buffer contains metadata */ BH_Prio, /* Buffer should be submitted with REQ_PRIO */ BH_Defer_Completion, /* Defer AIO completion to workqueue */ + BH_Read_Cb, /* Block's contents needs to be decrypted */ BH_PrivateStart,/* not a state bit, but the first bit available * for private allocation by other entities @@ -134,6 +135,7 @@ BUFFER_FNS(Unwritten, unwritten) BUFFER_FNS(Meta, meta) BUFFER_FNS(Prio, prio) BUFFER_FNS(Defer_Completion, defer_completion) +BUFFER_FNS(Read_Cb, read_cb) #define bh_offset(bh) ((unsigned long)(bh)->b_data & ~PAGE_MASK) -- 2.19.1