ext4: avoid divide by zero fault when deleting corrupted inline directories

A specially crafted file system can trick empty_inline_dir() into
reading past the last valid entry in a inline directory, and then run
into the end of xattr marker. This will trigger a divide by zero
fault.  Fix this by using the size of the inline directory instead of
dir->i_size.

Also clean up error reporting in __ext4_check_dir_entry so that the
message is clearer and more understandable --- and avoids the division
by zero trap if the size passed in is zero.  (I'm not sure why we
coded it that way in the first place; printing offset % size is
actually more confusing and less useful.)

https://bugzilla.kernel.org/show_bug.cgi?id=200933

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reported-by: Wen Xu <wen.xu@gatech.edu>
Cc: stable@vger.kernel.org

fs/ext4/dir.c

@@ -76,7 +76,7 @@ int __ext4_check_dir_entry(const char *function, unsigned int line,
 	else if (unlikely(rlen < EXT4_DIR_REC_LEN(de->name_len)))
 		error_msg = "rec_len is too small for name_len";
 	else if (unlikely(((char *) de - buf) + rlen > size))
-		error_msg = "directory entry across range";
+		error_msg = "directory entry overrun";
 	else if (unlikely(le32_to_cpu(de->inode) >
 			le32_to_cpu(EXT4_SB(dir->i_sb)->s_es->s_inodes_count)))
 		error_msg = "inode out of bounds";
@@ -85,18 +85,16 @@ int __ext4_check_dir_entry(const char *function, unsigned int line,
 
 	if (filp)
 		ext4_error_file(filp, function, line, bh->b_blocknr,
-				"bad entry in directory: %s - offset=%u(%u), "
-				"inode=%u, rec_len=%d, name_len=%d",
-				error_msg, (unsigned) (offset % size),
-				offset, le32_to_cpu(de->inode),
-				rlen, de->name_len);
+				"bad entry in directory: %s - offset=%u, "
+				"inode=%u, rec_len=%d, name_len=%d, size=%d",
+				error_msg, offset, le32_to_cpu(de->inode),
+				rlen, de->name_len, size);
 	else
 		ext4_error_inode(dir, function, line, bh->b_blocknr,
-				"bad entry in directory: %s - offset=%u(%u), "
-				"inode=%u, rec_len=%d, name_len=%d",
-				error_msg, (unsigned) (offset % size),
-				offset, le32_to_cpu(de->inode),
-				rlen, de->name_len);
+				"bad entry in directory: %s - offset=%u, "
+				"inode=%u, rec_len=%d, name_len=%d, size=%d",
+				 error_msg, offset, le32_to_cpu(de->inode),
+				 rlen, de->name_len, size);
 
 	return 1;
 }

fs/ext4/inline.c

@@ -1753,6 +1753,7 @@ bool empty_inline_dir(struct inode *dir, int *has_inline_data)
 {
 	int err, inline_size;
 	struct ext4_iloc iloc;
+	size_t inline_len;
 	void *inline_pos;
 	unsigned int offset;
 	struct ext4_dir_entry_2 *de;
@@ -1780,8 +1781,9 @@ bool empty_inline_dir(struct inode *dir, int *has_inline_data)
 		goto out;
 	}
 
+	inline_len = ext4_get_inline_size(dir);
 	offset = EXT4_INLINE_DOTDOT_SIZE;
-	while (offset < dir->i_size) {
+	while (offset < inline_len) {
 		de = ext4_get_inline_entry(dir, &iloc, offset,
 					   &inline_pos, &inline_size);
 		if (ext4_check_dir_entry(dir, NULL, de,