[PATCH v3] erofs-utils: fix battach on full buffer blocks

[Gao Xiang via Linux-erofs <linux-erofs@lists.ozlabs.org>]

From: Hu Weiwen <sehuww@mail.scut.edu.cn>

When the subsequent erofs_battach() is called on an buffer block of
which (bb->buffers.off % EROFS_BLKSIZ == 0), `tail_blkaddr' won't be
updated correctly. This bug can be reproduced by:

mkdir bug-repo
head -c 4032 /dev/urandom > bug-repo/1
head -c 4095 /dev/urandom > bug-repo/2
head -c 12345 /dev/urandom > bug-repo/3  # arbitrary size
mkfs.erofs -Eforce-inode-compact bug-repo.erofs.img bug-repo
Then mount this image and see that file `3' in the image is different
from `bug-repo/3'.

This patch fix this by:
 * Handle `oob' and `tail_blkaddr' for the case above properly;
 * Don't inline tail-packing data for such case, since the tail-packing
   data is actually in a different block from inode itself even kernel
   can handle such cases properly.

Signed-off-by: Hu Weiwen <sehuww@mail.scut.edu.cn>
Reviewed-by: Gao Xiang <hsiangkao@aol.com>
Signed-off-by: Gao Xiang <hsiangkao@aol.com>
---
changes since v2:
 - update commit message;
 - refine 2 asserts from < 0 to != EROFS_BLKSIZ.

 lib/cache.c    | 4 ++--
 lib/compress.c | 3 ++-
 lib/inode.c    | 2 +-
 3 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/lib/cache.c b/lib/cache.c
index 40d3b1f3f4d5..e3327c3f1586 100644
--- a/lib/cache.c
+++ b/lib/cache.c
@@ -102,7 +102,7 @@ static int __erofs_battach(struct erofs_buffer_block *bb,
 			   bool dryrun)
 {
 	const erofs_off_t alignedoffset = roundup(bb->buffers.off, alignsize);
-	const int oob = cmpsgn(roundup(bb->buffers.off % EROFS_BLKSIZ,
+	const int oob = cmpsgn(roundup((bb->buffers.off - 1) % EROFS_BLKSIZ + 1,
 				       alignsize) + incr + extrasize,
 			       EROFS_BLKSIZ);
 	bool tailupdate = false;
@@ -134,7 +134,7 @@ static int __erofs_battach(struct erofs_buffer_block *bb,
 			tail_blkaddr = blkaddr + BLK_ROUND_UP(bb->buffers.off);
 		erofs_bupdate_mapped(bb);
 	}
-	return (alignedoffset + incr) % EROFS_BLKSIZ;
+	return (alignedoffset + incr - 1) % EROFS_BLKSIZ + 1;
 }
 
 int erofs_bh_balloon(struct erofs_buffer_head *bh, erofs_off_t incr)
diff --git a/lib/compress.c b/lib/compress.c
index 2b1f93c389ff..4b685cd27080 100644
--- a/lib/compress.c
+++ b/lib/compress.c
@@ -456,8 +456,9 @@ int erofs_write_compressed_file(struct erofs_inode *inode)
 	vle_write_indexes_final(&ctx);
 
 	close(fd);
+	DBG_BUGON(!compressed_blocks);
 	ret = erofs_bh_balloon(bh, blknr_to_addr(compressed_blocks));
-	DBG_BUGON(ret);
+	DBG_BUGON(ret != EROFS_BLKSIZ);
 
 	erofs_info("compressed %s (%llu bytes) into %u blocks",
 		   inode->i_srcpath, (unsigned long long)inode->i_size,
diff --git a/lib/inode.c b/lib/inode.c
index 6371aa563673..40189fed37dd 100644
--- a/lib/inode.c
+++ b/lib/inode.c
@@ -531,7 +531,7 @@ int erofs_prepare_tail_block(struct erofs_inode *inode)
 	}
 	/* expend a block as the tail block (should be successful) */
 	ret = erofs_bh_balloon(bh, EROFS_BLKSIZ);
-	DBG_BUGON(ret);
+	DBG_BUGON(ret != EROFS_BLKSIZ);
 	return 0;
 }
 
-- 
2.24.0