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 <lasse.collin@tukaani.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Alain Knaff <alain@knaff.lu>
Cc: Albin Tonnerre <albin.tonnerre@free-electrons.com>
Cc: Phillip Lougher <phillip@lougher.demon.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/lib/decompress_unlzma.c b/lib/decompress_unlzma.c
index f30c899241ef..476c65af9709 100644
--- a/lib/decompress_unlzma.c
+++ b/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;