[PATCH master] fs: ext4: fix bogus behavior on failure to read ext4 block

[Ahmad Fatoum]

The conversion of blknr from a signed 32-bit to an unsigned 64-type resulted
in the check for error to never return true. Fix this.

Affected configuration would behave incorrectly when served with invalid
blocks. Instead of aborting and having the filesystem bubble up an error
code, it would return invalid data. As there is no ext4 write support,
this wouldn't lead to ext4 data corruption however.

Reported-by: Bastian Krause <bst at pengutronix.de>
Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
---
 fs/ext4/ext4fs.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/ext4/ext4fs.c b/fs/ext4/ext4fs.c
index 54349aad3f3f..344d423fd9c4 100644
--- a/fs/ext4/ext4fs.c
+++ b/fs/ext4/ext4fs.c
@@ -74,11 +74,11 @@ loff_t ext4fs_read_file(struct ext2fs_node *node, loff_t pos,
 		loff_t blockend = blocksize;
 		loff_t skipfirst = 0;
 
-		blknr = read_allocated_block(node, i);
-		if (blknr < 0)
-			return blknr;
+		ret = read_allocated_block(node, i);
+		if (ret < 0)
+			return ret;
 
-		blknr = blknr << log2blocksize;
+		blknr = ret << log2blocksize;
 
 		/* Last block.  */
 		if (i == blockcnt - 1) {
-- 
2.29.2