[PATCH] fs/squashfs: fix reading of fragmented files

[Joao Marcos Costa]

The fragmented files were not correctly read because of two issues:

- The squashfs_file_info struct has a field named 'comp', which tells if
the file's fragment is compressed or not. This field was always set to
'true' in sqfs_get_regfile_info and sqfs_get_lregfile_info. It should
actually take sqfs_frag_lookup's return value. This patch addresses
these two assignments.

- In sqfs_read, the fragments (compressed or not) were copied to the
output buffer through a for loop which was reading data at the wrong
offset. Replace these loops by equivalent calls to memcpy, with the
right parameters.

I tested this patch by comparing the MD5 checksum of a few fragmented
files with the respective md5sum output in sandbox, considering both
compressed and uncompressed fragments.

Signed-off-by: Joao Marcos Costa <jmcosta944 at gmail.com>
---
 fs/squashfs/sqfs.c | 16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

diff --git a/fs/squashfs/sqfs.c b/fs/squashfs/sqfs.c
index 29805c3c6f..22ef4f2691 100644
--- a/fs/squashfs/sqfs.c
+++ b/fs/squashfs/sqfs.c
@@ -1253,7 +1253,7 @@ static int sqfs_get_regfile_info(struct squashfs_reg_inode *reg,
 				       fentry);
 		if (ret < 0)
 			return -EINVAL;
-		finfo->comp = true;
+		finfo->comp = ret;
 		if (fentry->size < 1 || fentry->start == 0x7FFFFFFF)
 			return -EINVAL;
 	} else {
@@ -1291,7 +1291,7 @@ static int sqfs_get_lregfile_info(struct squashfs_lreg_inode *lreg,
 				       fentry);
 		if (ret < 0)
 			return -EINVAL;
-		finfo->comp = true;
+		finfo->comp = ret;
 		if (fentry->size < 1 || fentry->start == 0x7FFFFFFF)
 			return -EINVAL;
 	} else {
@@ -1547,20 +1547,16 @@ int sqfs_read(const char *filename, void *buf, loff_t offset, loff_t len,
 			goto out;
 		}
 
-		for (j = *actread; j < finfo.size; j++) {
-			memcpy(buf + j, &fragment_block[finfo.offset + j], 1);
-			(*actread)++;
-		}
+		memcpy(buf + *actread, &fragment_block[finfo.offset], finfo.size - *actread);
+		*actread = finfo.size;
 
 		free(fragment_block);
 
 	} else if (finfo.frag && !finfo.comp) {
 		fragment_block = (void *)fragment + table_offset;
 
-		for (j = *actread; j < finfo.size; j++) {
-			memcpy(buf + j, &fragment_block[finfo.offset + j], 1);
-			(*actread)++;
-		}
+		memcpy(buf + *actread, &fragment_block[finfo.offset], finfo.size - *actread);
+		*actread = finfo.size;
 	}
 
 out:
-- 
2.25.1