[PATCH v5] fs/ntfs3: Validate parameter bytes and valid size

[eadavis@sina.com]

From: eadaivs <eadaivs@sina.com>

Syzbot reports a slab out of bounds read in ntfs_get_ea,
According to splat, the final problem is in the function find_ea,

1) If parameter "bytes" less than the structure EA_ FULL Pointer Object Size,
then the unpacked_ea_size() is an out of bounds read.

2) The *off + unpacked_ea_size() can have an integer overflow.

Change the type of the parameter bytes to size_t,
add sanity check for ensuring that the parameter bytes within reason.
And instead of calculating the offset, use the function size add.

Link: https://syzkaller.appspot.com/bug?extid=c4d950787fd5553287b7
Reported-and-tested-by: syzbot+c4d950787fd5553287b7@syzkaller.appspotmail.com
Fixes: (be71b5cba2e6) fs/ntfs3: Add attrib operations
Signed-off-by: eadaivs <eadaivs@sina.com>
---
Changes in v5:
  Refactor the code and pass syzbot test.

 fs/ntfs3/xattr.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/fs/ntfs3/xattr.c b/fs/ntfs3/xattr.c
index afd0ddad826f..188a76c28233 100644
--- a/fs/ntfs3/xattr.c
+++ b/fs/ntfs3/xattr.c
@@ -41,17 +41,23 @@ static inline size_t packed_ea_size(const struct EA_FULL *ea)
  *
  * Assume there is at least one xattr in the list.
  */
-static inline bool find_ea(const struct EA_FULL *ea_all, u32 bytes,
+static inline bool find_ea(const struct EA_FULL *ea_all, size_t bytes,
 			   const char *name, u8 name_len, u32 *off)
 {
+	const struct EA_FULL *eb;
+	u32 next_off;
 	*off = 0;
 
-	if (!ea_all || !bytes)
+	if (!ea_all || bytes < sizeof(*eb))
 		return false;
 
 	for (;;) {
 		const struct EA_FULL *ea = Add2Ptr(ea_all, *off);
-		u32 next_off = *off + unpacked_ea_size(ea);
+
+		if (sizeof(*ea) + *off > bytes)
+			return false;
+
+		next_off = size_add(*off, unpacked_ea_size(ea));
 
 		if (next_off > bytes)
 			return false;
@@ -61,8 +67,6 @@ static inline bool find_ea(const struct EA_FULL *ea_all, u32 bytes,
 			return true;
 
 		*off = next_off;
-		if (next_off >= bytes)
-			return false;
 	}
 }
 
-- 
2.37.2