From 04f052c56ded5ab6a904e3a264a73dc0412b2e78 Mon Sep 17 00:00:00 2001 From: Denys Vlasenko Date: Tue, 15 Jun 2021 15:07:57 +0200 Subject: [PATCH] unlzma: fix a case where we could read before beginning of buffer Cc: pavel@zhukoff.net Testcase: 21 01 01 00 00 00 00 00 e7 01 01 01 ef 00 df b6 00 17 02 10 11 0f ff 00 16 00 00 Unfortunately, the bug is not reliably causing a segfault, the behavior depends on what's in memory before the buffer. function old new delta unpack_lzma_stream 2762 2768 +6 Signed-off-by: Denys Vlasenko Signed-off-by: Pavel Zhukov CVE: CVE-2021-42374 Upstream-Status: Backport [https://git.busybox.net/busybox/commit/?h=1_33_stable&id=d326be2850ea2bd78fe2c22d6c45c3b861d82937] Comment: testdata dropped because of binary format --- archival/libarchive/decompress_unlzma.c | 5 ++++- testsuite/unlzma.tests | 17 +++++++++++++---- testsuite/unlzma_issue_3.lzma | Bin 0 -> 27 bytes 3 files changed, 17 insertions(+), 5 deletions(-) create mode 100644 testsuite/unlzma_issue_3.lzma diff --git a/archival/libarchive/decompress_unlzma.c b/archival/libarchive/decompress_unlzma.c index 0744f231a1d64d92676b0cada2342f88f3b39b31..fb5aac8fe9ea0c53e0c2d7a7cbd05a753e39bc9d 100644 --- a/archival/libarchive/decompress_unlzma.c +++ b/archival/libarchive/decompress_unlzma.c @@ -290,8 +290,11 @@ unpack_lzma_stream(transformer_state_t *xstate) uint32_t pos; pos = buffer_pos - rep0; - if ((int32_t)pos < 0) + if ((int32_t)pos < 0) { pos += header.dict_size; + if ((int32_t)pos < 0) + goto bad; + } match_byte = buffer[pos]; do { int bit; -- 2.34.0