[PATCH-for-5.2 1/3] fuzz: fix writing DMA patterns

[Alexander Bulekov]

This code had all sorts of issues. We used a loop similar to
address_space_write_rom, but I did not remove a "break" that only made
sense in the context of the switch statement in the original code. Then,
after the loop, we did a separate qtest_memwrite over the entire DMA
access range, defeating the purpose of the loop. Additionally, we
increment the buf pointer, and then try to g_free() it. Fix these
problems.

Reported-by: OSS-Fuzz (Issue 26725)
Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
---
 tests/qtest/fuzz/generic_fuzz.c | 37 +++++++++++++++------------------
 1 file changed, 17 insertions(+), 20 deletions(-)

diff --git a/tests/qtest/fuzz/generic_fuzz.c b/tests/qtest/fuzz/generic_fuzz.c
index a8f5864883..3e2d50feaa 100644
--- a/tests/qtest/fuzz/generic_fuzz.c
+++ b/tests/qtest/fuzz/generic_fuzz.c
@@ -229,10 +229,10 @@ void fuzz_dma_read_cb(size_t addr, size_t len, 
MemoryRegion *mr, bool is_write)
     address_range ar = {addr, len};
     g_array_append_val(dma_regions, ar);
     pattern p = g_array_index(dma_patterns, pattern, dma_pattern_index);
-    void *buf = pattern_alloc(p, ar.size);
+    void *buf_base = pattern_alloc(p, ar.size);
+    void *buf = buf_base;
     hwaddr l, addr1;
     MemoryRegion *mr1;
-    uint8_t *ram_ptr;
     while (len > 0) {
         l = len;
         mr1 = address_space_translate(first_cpu->as,
@@ -244,30 +244,27 @@ void fuzz_dma_read_cb(size_t addr, size_t len, 
MemoryRegion *mr, bool is_write)
             l = memory_access_size(mr1, l, addr1);
         } else {
             /* ROM/RAM case */
-            ram_ptr = qemu_map_ram_ptr(mr1->ram_block, addr1);
-            memcpy(ram_ptr, buf, l);
-            break;
+            if (qtest_log_enabled) {
+                /*
+                * With QTEST_LOG, use a normal, slow QTest memwrite. Prefix 
the log
+                * that will be written by qtest.c with a DMA tag, so we can 
reorder
+                * the resulting QTest trace so the DMA fills precede the last 
PIO/MMIO
+                * command.
+                */
+                fprintf(stderr, "[DMA] ");
+                if (double_fetch) {
+                    fprintf(stderr, "[DOUBLE-FETCH] ");
+                }
+                fflush(stderr);
+            }
+            qtest_memwrite(qts_global, addr, buf, l);
         }
         len -= l;
         buf += l;
         addr += l;
 
     }
-    if (qtest_log_enabled) {
-        /*
-         * With QTEST_LOG, use a normal, slow QTest memwrite. Prefix the log
-         * that will be written by qtest.c with a DMA tag, so we can reorder
-         * the resulting QTest trace so the DMA fills precede the last PIO/MMIO
-         * command.
-         */
-        fprintf(stderr, "[DMA] ");
-        if (double_fetch) {
-            fprintf(stderr, "[DOUBLE-FETCH] ");
-        }
-        fflush(stderr);
-    }
-    qtest_memwrite(qts_global, ar.addr, buf, ar.size);
-    g_free(buf);
+    g_free(buf_base);
 
     /* Increment the index of the pattern for the next DMA access */
     dma_pattern_index = (dma_pattern_index + 1) % dma_patterns->len;
-- 
2.28.0