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[Qemu-devel] [PATCH] spapr: fix out of bounds write in spapr_populate_dr

From: Fabiano Rosas
Subject: [Qemu-devel] [PATCH] spapr: fix out of bounds write in spapr_populate_drmem_v2
Date: Wed, 13 Feb 2019 15:29:26 -0200

buf_len is uint8_t which is not large enough to hold the result of:

  nr_entries * sizeof(struct sPAPRDrconfCellV2) + sizeof(uint32_t);

for a nr_entries greater than 10.

This causes the allocated buffer 'int_buf' to be smaller than expected
and we eventually overwrite some of glibc's control structures (see
"chunk" in https://sourceware.org/glibc/wiki/MallocInternals)

The following error is seen while trying to free int_buf:

  "free(): invalid next size (fast)"

Fixes: a324d6f166 "spapr: Support ibm,dynamic-memory-v2 property"
Signed-off-by: Fabiano Rosas <address@hidden>
 hw/ppc/spapr.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index 332cba89d4..7c4bf8ed8c 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -687,14 +687,14 @@ static int spapr_populate_drmem_v2(sPAPRMachineState 
*spapr, void *fdt,
                                    int offset, MemoryDeviceInfoList *dimms)
     MachineState *machine = MACHINE(spapr);
-    uint8_t *int_buf, *cur_index, buf_len;
+    uint8_t *int_buf, *cur_index;
     int ret;
     uint64_t lmb_size = SPAPR_MEMORY_BLOCK_SIZE;
     uint64_t addr, cur_addr, size;
     uint32_t nr_boot_lmbs = (machine->device_memory->base / lmb_size);
     uint64_t mem_end = machine->device_memory->base +
-    uint32_t node, nr_entries = 0;
+    uint32_t node, buf_len, nr_entries = 0;
     sPAPRDRConnector *drc;
     DrconfCellQueue *elem, *next;
     MemoryDeviceInfoList *info;

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