hfsplus: fix possible deadlock when handling corrupted extents

A corrupted extent for the extent file itself may try to get an impossible
extent, causing a deadlock if I see it correctly.

Check the inode number after the first_blocks checks and fail if it's the
extent file, as according to the spec the extent file should have no
extent for itself.
Signed-off-by: NEric Sesterhenn <snakebyte@gmx.de>
Cc: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

fs/hfsplus/extents.c

@@ -199,6 +199,9 @@ int hfsplus_get_block(struct inode *inode, sector_t iblock,
 		goto done;
 	}
 
+	if (inode->i_ino == HFSPLUS_EXT_CNID)
+		return -EIO;
+
 	mutex_lock(&HFSPLUS_I(inode).extents_lock);
 	res = hfsplus_ext_read_extent(inode, ablock);
 	if (!res) {