[PULL 02/17] block/accounting: take stats->lock in latency histogram setters

From: "Denis V. Lunev" <[email protected]>

block_latency_histogram_set() and block_latency_histograms_clear()
replace BlockLatencyHistogram's nbins/boundaries/bins without taking
stats->lock, while block_account_one_io() reads those same fields
under that lock from whatever iothread completes the I/O. The result
is usual use-after-free and qemu crash.

Take stats->lock in both setters, matching the lock already held by
the reader.

Signed-off-by: Denis V. Lunev <[email protected]>
CC: Kevin Wolf <[email protected]>
CC: Hanna Reitz <[email protected]>
CC: Vladimir Sementsov-Ogievskiy <[email protected]>
CC: Andrey Drobyshev <[email protected]>
Message-ID: <[email protected]>
Reviewed-by: Kevin Wolf <[email protected]>
Signed-off-by: Kevin Wolf <[email protected]>
---
 block/accounting.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/block/accounting.c b/block/accounting.c
index f00fe997403..6e06c7609eb 100644
--- a/block/accounting.c
+++ b/block/accounting.c
@@ -194,6 +194,8 @@ int block_latency_histogram_set(BlockAcctStats *stats, enum BlockAcctType type,
         return -EINVAL;
     }
 
+    qemu_mutex_lock(&stats->lock);
+
     hist->nbins = new_nbins;
     g_free(hist->boundaries);
     hist->boundaries = g_new(uint64_t, hist->nbins - 1);
@@ -206,6 +208,8 @@ int block_latency_histogram_set(BlockAcctStats *stats, enum BlockAcctType type,
     g_free(hist->bins);
     hist->bins = g_new0(uint64_t, hist->nbins);
 
+    qemu_mutex_unlock(&stats->lock);
+
     return 0;
 }
 
@@ -213,12 +217,16 @@ void block_latency_histograms_clear(BlockAcctStats *stats)
 {
     int i;
 
+    qemu_mutex_lock(&stats->lock);
+
     for (i = 0; i < BLOCK_MAX_IOTYPE; i++) {
         BlockLatencyHistogram *hist = &stats->latency_histogram[i];
         g_free(hist->bins);
         g_free(hist->boundaries);
         memset(hist, 0, sizeof(*hist));
     }
+
+    qemu_mutex_unlock(&stats->lock);
 }
 
 static void block_account_one_io(BlockAcctStats *stats, BlockAcctCookie *cookie,
-- 
2.55.0