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 <chandan@xxxxxxxxxxxxx>
---
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
