bcachefs: Remove incorrect __counted_by annotation

commit 6846100b00d97d3d6f05766ae86a0d821d849e78 upstream.

This actually reverts 86e92ee ("bcachefs: Annotate struct bch_xattr
with __counted_by()").

After the x_name, there is a value. According to the disscussion[1],
__counted_by assumes that the flexible array member contains exactly
the amount of elements that are specified. Now there are users came across
a false positive detection of an out of bounds write caused by
the __counted_by here[2], so revert that.

[1] https://lore.kernel.org/lkml/Zv8VDKWN1GzLRT-_@archlinux/T/#m0ce9541c5070146320efd4f928cc1ff8de69e9b2
[2] https://privatebin.net/?a0d4e97d590d71e1#9bLmp2Kb5NU6X6cZEucchDcu88HzUQwHUah8okKPReEt

Signed-off-by: Alan Huang <[email protected]>
Signed-off-by: Kent Overstreet <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
(cherry picked from commit 6b6cd389104c2dc34dbdea2b1ba48fea8c39b24e)
Signed-off-by: Jack Vogel <[email protected]>

Author: alanskind

fs/bcachefs/xattr_format.h

@@ -13,7 +13,13 @@ struct bch_xattr {
 	__u8			x_type;
 	__u8			x_name_len;
 	__le16			x_val_len;
-	__u8			x_name[] __counted_by(x_name_len);
+	/*
+	 * x_name contains the name and value counted by
+	 * x_name_len + x_val_len. The introduction of
+	 * __counted_by(x_name_len) caused a false positive
+	 * detection of an out of bounds write.
+	 */
+	__u8			x_name[];
 } __packed __aligned(8);
 
 #endif /* _BCACHEFS_XATTR_FORMAT_H */