lib/xz: Avoid overlapping memcpy() with invalid input with in-place decompression

[linux-2.6-microblaze.git] / lib / xz / xz_dec_lzma2.c

diff --git a/lib/xz/xz_dec_lzma2.c b/lib/xz/xz_dec_lzma2.c
index 7a6781e..d548cf0 100644 (file)
--- a/lib/xz/xz_dec_lzma2.c
+++ b/lib/xz/xz_dec_lzma2.c
@@ -387,7 +387,14 @@ static void dict_uncompressed(struct dictionary *dict, struct xz_buf *b,
 
                *left -= copy_size;
 
-               memcpy(dict->buf + dict->pos, b->in + b->in_pos, copy_size);
+               /*
+                * If doing in-place decompression in single-call mode and the
+                * uncompressed size of the file is larger than the caller
+                * thought (i.e. it is invalid input!), the buffers below may
+                * overlap and cause undefined behavior with memcpy().
+                * With valid inputs memcpy() would be fine here.
+                */
+               memmove(dict->buf + dict->pos, b->in + b->in_pos, copy_size);
                dict->pos += copy_size;
 
                if (dict->full < dict->pos)
@@ -397,7 +404,11 @@ static void dict_uncompressed(struct dictionary *dict, struct xz_buf *b,
                        if (dict->pos == dict->end)
                                dict->pos = 0;
 
-                       memcpy(b->out + b->out_pos, b->in + b->in_pos,
+                       /*
+                        * Like above but for multi-call mode: use memmove()
+                        * to avoid undefined behavior with invalid input.
+                        */
+                       memmove(b->out + b->out_pos, b->in + b->in_pos,
                                        copy_size);
                }
 
@@ -421,6 +432,12 @@ static uint32_t dict_flush(struct dictionary *dict, struct xz_buf *b)
                if (dict->pos == dict->end)
                        dict->pos = 0;
 
+               /*
+                * These buffers cannot overlap even if doing in-place
+                * decompression because in multi-call mode dict->buf
+                * has been allocated by us in this file; it's not
+                * provided by the caller like in single-call mode.
+                */
                memcpy(b->out + b->out_pos, dict->buf + dict->start,
                                copy_size);
        }