busybox-1.27.2: Fix lzma segfaults

[No upstream tracking] -- https://bugs.busybox.net/show_bug.cgi?id=10871

libarchive: check buffer index in lzma_decompress

With specific defconfig busybox fails to check zip fileheader magic
(archival/unzip.c) and uses (archival/libarchive/decompress_unlzma.c)
for decompression which leads to segmentation fault. It prevents accessing into
buffer, which is smaller than pos index. Patch includes multiple segmentation
fault fixes.

Upstream-Status: Backport [https://git.busybox.net/busybox/commit/?id=a36986bb80289c1cd8d15a557e49207c9a42946b]
bug: 10436 10871
Signed-off-by: Andrej Valek <andrej.valek@siemens.com>

diff --git a/archival/libarchive/decompress_unlzma.c b/archival/libarchive/decompress_unlzma.c
index a904087..29eee2a 100644
--- a/archival/libarchive/decompress_unlzma.c
+++ b/archival/libarchive/decompress_unlzma.c
@@ -11,6 +11,14 @@
 #include "libbb.h"
 #include "bb_archive.h"
 
+
+#if 0
+# define dbg(...) bb_error_msg(__VA_ARGS__)
+#else
+# define dbg(...) ((void)0)
+#endif
+
+
 #if ENABLE_FEATURE_LZMA_FAST
 #  define speed_inline ALWAYS_INLINE
 #  define size_inline
@@ -217,6 +225,7 @@ unpack_lzma_stream(transformer_state_t *xstate)
 	rc_t *rc;
 	int i;
 	uint8_t *buffer;
+	uint32_t buffer_size;
 	uint8_t previous_byte = 0;
 	size_t buffer_pos = 0, global_pos = 0;
 	int len = 0;
@@ -246,7 +255,8 @@ unpack_lzma_stream(transformer_state_t *xstate)
 	if (header.dict_size == 0)
 		header.dict_size++;
 
-	buffer = xmalloc(MIN(header.dst_size, header.dict_size));
+	buffer_size = MIN(header.dst_size, header.dict_size);
+	buffer = xmalloc(buffer_size);
 
 	{
 		int num_probs;
@@ -341,8 +351,12 @@ unpack_lzma_stream(transformer_state_t *xstate)
 						state = state < LZMA_NUM_LIT_STATES ? 9 : 11;
 
 						pos = buffer_pos - rep0;
-						if ((int32_t)pos < 0)
+						if ((int32_t)pos < 0) {
 							pos += header.dict_size;
+							/* see unzip_bad_lzma_2.zip: */
+							if (pos >= buffer_size)
+								goto bad;
+						}
 						previous_byte = buffer[pos];
 						goto one_byte1;
 #else
@@ -417,6 +431,10 @@ unpack_lzma_stream(transformer_state_t *xstate)
 						for (; num_bits2 != LZMA_NUM_ALIGN_BITS; num_bits2--)
 							rep0 = (rep0 << 1) | rc_direct_bit(rc);
 						rep0 <<= LZMA_NUM_ALIGN_BITS;
+						if ((int32_t)rep0 < 0) {
+							dbg("%d rep0:%d", __LINE__, rep0);
+							goto bad;
+						}
 						prob3 = p + LZMA_ALIGN;
 					}
 					i2 = 1;
@@ -450,8 +468,12 @@ unpack_lzma_stream(transformer_state_t *xstate)
  IF_NOT_FEATURE_LZMA_FAST(string:)
 			do {
 				uint32_t pos = buffer_pos - rep0;
-				if ((int32_t)pos < 0)
+				if ((int32_t)pos < 0) {
 					pos += header.dict_size;
+					/* more stringent test (see unzip_bad_lzma_1.zip): */
+					if (pos >= buffer_size)
+						goto bad;
+				}
 				previous_byte = buffer[pos];
  IF_NOT_FEATURE_LZMA_FAST(one_byte2:)
 				buffer[buffer_pos++] = previous_byte;
@@ -478,6 +500,12 @@ unpack_lzma_stream(transformer_state_t *xstate)
 		IF_DESKTOP(total_written += buffer_pos;)
 		if (transformer_write(xstate, buffer, buffer_pos) != (ssize_t)buffer_pos) {
  bad:
+			/* One of our users, bbunpack(), expects _us_ to emit
+			 * the error message (since it's the best place to give
+			 * potentially more detailed information).
+			 * Do not fail silently.
+			 */
+			bb_error_msg("corrupted data");
 			total_written = -1; /* failure */
 		}
 		rc_free(rc);