fs/buffer.c: support fscrypt in block_read_full_page()

After each filesystem block (as represented by a buffer_head) has been
read from disk by block_read_full_page(), decrypt it if needed.  The
decryption is done on the fscrypt_read_workqueue.

This is the final change needed to support ext4 encryption with
blocksize != PAGE_SIZE, and it's a fairly small change now that
CONFIG_FS_ENCRYPTION is a bool and fs/crypto/ exposes functions to
decrypt individual blocks and to enqueue work on the fscrypt workqueue.

Don't try to add fs-verity support yet, as the fs/verity/ support layer
isn't ready for sub-page blocks yet.  Just add fscrypt support for now.

Almost all the new code is compiled away when CONFIG_FS_ENCRYPTION=n.

Cc: Chandan Rajendra <chandan@linux.ibm.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20191023033312.361355-2-ebiggers@kernel.org
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/buffer.c b/fs/buffer.c
index 86a38b9..d398380 100644 (file)
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -47,6 +47,7 @@
 #include <linux/pagevec.h>
 #include <linux/sched/mm.h>
 #include <trace/events/block.h>
+#include <linux/fscrypt.h>
 
 static int fsync_buffers_list(spinlock_t *lock, struct list_head *list);
 static int submit_bh_wbc(int op, int op_flags, struct buffer_head *bh,
@@ -246,10 +247,6 @@ out:
        return ret;
 }
 
-/*
- * I/O completion handler for block_read_full_page() - pages
- * which come unlocked at the end of I/O.
- */
 static void end_buffer_async_read(struct buffer_head *bh, int uptodate)
 {
        unsigned long flags;
@@ -307,6 +304,47 @@ still_busy:
        return;
 }
 
+struct decrypt_bh_ctx {
+       struct work_struct work;
+       struct buffer_head *bh;
+};
+
+static void decrypt_bh(struct work_struct *work)
+{
+       struct decrypt_bh_ctx *ctx =
+               container_of(work, struct decrypt_bh_ctx, work);
+       struct buffer_head *bh = ctx->bh;
+       int err;
+
+       err = fscrypt_decrypt_pagecache_blocks(bh->b_page, bh->b_size,
+                                              bh_offset(bh));
+       end_buffer_async_read(bh, err == 0);
+       kfree(ctx);
+}
+
+/*
+ * I/O completion handler for block_read_full_page() - pages
+ * which come unlocked at the end of I/O.
+ */
+static void end_buffer_async_read_io(struct buffer_head *bh, int uptodate)
+{
+       /* Decrypt if needed */
+       if (uptodate && IS_ENABLED(CONFIG_FS_ENCRYPTION) &&
+           IS_ENCRYPTED(bh->b_page->mapping->host) &&
+           S_ISREG(bh->b_page->mapping->host->i_mode)) {
+               struct decrypt_bh_ctx *ctx = kmalloc(sizeof(*ctx), GFP_ATOMIC);
+
+               if (ctx) {
+                       INIT_WORK(&ctx->work, decrypt_bh);
+                       ctx->bh = bh;
+                       fscrypt_enqueue_decrypt_work(&ctx->work);
+                       return;
+               }
+               uptodate = 0;
+       }
+       end_buffer_async_read(bh, uptodate);
+}
+
 /*
  * Completion handler for block_write_full_page() - pages which are unlocked
  * during I/O, and which have PageWriteback cleared upon I/O completion.
@@ -379,7 +417,7 @@ EXPORT_SYMBOL(end_buffer_async_write);
  */
 static void mark_buffer_async_read(struct buffer_head *bh)
 {
-       bh->b_end_io = end_buffer_async_read;
+       bh->b_end_io = end_buffer_async_read_io;
        set_buffer_async_read(bh);
 }