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author | Lasse Collin <lasse.collin@tukaani.org> | 2020-02-03 00:18:32 +0200 |
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committer | Lasse Collin <lasse.collin@tukaani.org> | 2020-02-03 00:18:32 +0200 |
commit | cfc1499e9fc23d8caa6dfdf1cc3ccf60d6fcd947 (patch) | |
tree | dc3e070899450cfc8e6453e8b0e0c42c49cb5506 /linux/lib/xz | |
parent | 40d291b609d0cc6344f3e26ed34b4fd755e403da (diff) | |
download | xz-embedded-cfc1499e9fc23d8caa6dfdf1cc3ccf60d6fcd947.tar.gz |
Avoid overlapping memcpy() with invalid input with in-place decompression.
With valid files, the safety margin described in lib/decompress_unxz.c
ensures that these buffers cannot overlap. But if the uncompressed size
of the input is larger than the caller thought, which is possible when
the input file is invalid/corrupt, the buffers can overlap. Obviously
the result will then be garbage (and usually the decoder will return
an error too) but no other harm will happen when such an over-run occurs.
This change only affects uncompressed LZMA2 chunks and so this
should have no effect on performance.
Diffstat (limited to 'linux/lib/xz')
-rw-r--r-- | linux/lib/xz/xz_dec_lzma2.c | 21 |
1 files changed, 19 insertions, 2 deletions
diff --git a/linux/lib/xz/xz_dec_lzma2.c b/linux/lib/xz/xz_dec_lzma2.c index 156f26f..dd80989 100644 --- a/linux/lib/xz/xz_dec_lzma2.c +++ b/linux/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); } |