Decompressors: validate match distance in decompress_unlzma.c

Validate the newly decoded distance (rep0) in process_bit1().  This is to
detect corrupt LZMA data quickly.  The old code can run for long time
producing garbage until it hits the end of the input.

Signed-off-by: Lasse Collin <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Alain Knaff <[email protected]>
Cc: Albin Tonnerre <[email protected]>
Cc: Phillip Lougher <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

lib/decompress_unlzma.c

@@ -522,6 +522,9 @@ static inline int INIT process_bit1(struct writer *wr, struct rc *rc,
 			cst->rep0 = pos_slot;
 		if (++(cst->rep0) == 0)
 			return 0;
+		if (cst->rep0 > wr->header->dict_size
+				|| cst->rep0 > get_pos(wr))
+			return -1;
 	}
 
 	len += LZMA_MATCH_MIN_LEN;