From 65a23f5dbee4497064e9bb467f81138a62b0dae1 Mon Sep 17 00:00:00 2001
From: Daniel Axtens <dja@axtens.net>
Date: Tue, 1 Jan 2019 16:01:40 +1100
Subject: [PATCH 2/2] 7zip: fix crash when parsing certain archives
Fuzzing with CRCs disabled revealed that a call to get_uncompressed_data()
would sometimes fail to return at least 'minimum' bytes. This can cause
the crc32() invocation in header_bytes to read off into invalid memory.
A specially crafted archive can use this to cause a crash.
An ASAN trace is below, but ASAN is not required - an uninstrumented
binary will also crash.
==7719==ERROR: AddressSanitizer: SEGV on unknown address 0x631000040000 (pc 0x7fbdb3b3ec1d bp 0x7ffe77a51310 sp 0x7ffe77a51150 T0)
==7719==The signal is caused by a READ memory access.
#0 0x7fbdb3b3ec1c in crc32_z (/lib/x86_64-linux-gnu/libz.so.1+0x2c1c)
#1 0x84f5eb in header_bytes (/tmp/libarchive/bsdtar+0x84f5eb)
#2 0x856156 in read_Header (/tmp/libarchive/bsdtar+0x856156)
#3 0x84e134 in slurp_central_directory (/tmp/libarchive/bsdtar+0x84e134)
#4 0x849690 in archive_read_format_7zip_read_header (/tmp/libarchive/bsdtar+0x849690)
#5 0x5713b7 in _archive_read_next_header2 (/tmp/libarchive/bsdtar+0x5713b7)
#6 0x570e63 in _archive_read_next_header (/tmp/libarchive/bsdtar+0x570e63)
#7 0x6f08bd in archive_read_next_header (/tmp/libarchive/bsdtar+0x6f08bd)
#8 0x52373f in read_archive (/tmp/libarchive/bsdtar+0x52373f)
#9 0x5257be in tar_mode_x (/tmp/libarchive/bsdtar+0x5257be)
#10 0x51daeb in main (/tmp/libarchive/bsdtar+0x51daeb)
#11 0x7fbdb27cab96 in __libc_start_main /build/glibc-OTsEL5/glibc-2.27/csu/../csu/libc-start.c:310
#12 0x41dd09 in _start (/tmp/libarchive/bsdtar+0x41dd09)
This was primarly done with afl and FairFuzz. Some early corpus entries
may have been generated by qsym.
---
libarchive/archive_read_support_format_7zip.c | 8 +-------
1 file changed, 1 insertion(+), 7 deletions(-)
diff --git a/libarchive/archive_read_support_format_7zip.c b/libarchive/archive_read_support_format_7zip.c
index bccbf896..b6d1505d 100644
--- a/libarchive/archive_read_support_format_7zip.c
+++ b/libarchive/archive_read_support_format_7zip.c
@@ -2964,13 +2964,7 @@ get_uncompressed_data(struct archive_read *a, const void **buff, size_t size,
if (zip->codec == _7Z_COPY && zip->codec2 == (unsigned long)-1) {
/* Copy mode. */
- /*
- * Note: '1' here is a performance optimization.
- * Recall that the decompression layer returns a count of
- * available bytes; asking for more than that forces the
- * decompressor to combine reads by copying data.
- */
- *buff = __archive_read_ahead(a, 1, &bytes_avail);
+ *buff = __archive_read_ahead(a, minimum, &bytes_avail);
if (bytes_avail <= 0) {
archive_set_error(&a->archive,
ARCHIVE_ERRNO_FILE_FORMAT,
--
2.20.1