Passing an empty list of boundaries to block-latency-histogram-set sets
up a state that leads to a NULL pointer dereference when the next
request should be accounted for. This is not a useful configuration, so
just error out if the user tries to set it.
The crash can easily be reproduced with the following script:
qmp() {
cat <<EOF
{'execute':'qmp_capabilities'}
{'execute':'block-latency-histogram-set',
'arguments': {'id':'ide0','boundaries':[]}}
{'execute':'cont'}
EOF
}
qmp | ./qemu-system-x86_64 -S -qmp stdio \
-drive if=none,format=raw,file=null-co:// \
-device ide-hd,drive=none0,id=ide0
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20260331102608.60882-1-kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
block/accounting.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/block/accounting.c b/block/accounting.c
index 5cf51f029b1..f00fe997403 100644
--- a/block/accounting.c
+++ b/block/accounting.c
@@ -185,6 +185,15 @@ int block_latency_histogram_set(BlockAcctStats *stats, enum BlockAcctType type,
prev = entry->value;
}
+ /*
+ * block_latency_histogram_account() assumes that it can always access
+ * hist->boundaries[0], so require at least one boundary. A histogram with
+ * a single bin is useless anyway.
+ */
+ if (new_nbins <= 1) {
+ return -EINVAL;
+ }
+
hist->nbins = new_nbins;
g_free(hist->boundaries);
hist->boundaries = g_new(uint64_t, hist->nbins - 1);
--
2.53.0