[Qemu-stable] [PULL 16/17] block/nfs: limit maximum readahead size to 1MB

[Stefan Hajnoczi]

From: Peter Lieven <address@hidden>

a malicious caller could otherwise specify a very
large value via the URI and force libnfs to allocate
a large amount of memory for the readahead buffer.

Cc: address@hidden
Signed-off-by: Peter Lieven <address@hidden>
Message-id: address@hidden
Signed-off-by: Stefan Hajnoczi <address@hidden>
---
 block/nfs.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/block/nfs.c b/block/nfs.c
index ca9e24e..c026ff6 100644
--- a/block/nfs.c
+++ b/block/nfs.c
@@ -35,6 +35,8 @@
 #include "sysemu/sysemu.h"
 #include <nfsc/libnfs.h>
 
+#define QEMU_NFS_MAX_READAHEAD_SIZE 1048576
+
 typedef struct NFSClient {
     struct nfs_context *context;
     struct nfsfh *fh;
@@ -327,6 +329,11 @@ static int64_t nfs_client_open(NFSClient *client, const 
char *filename,
             nfs_set_tcp_syncnt(client->context, val);
 #ifdef LIBNFS_FEATURE_READAHEAD
         } else if (!strcmp(qp->p[i].name, "readahead")) {
+            if (val > QEMU_NFS_MAX_READAHEAD_SIZE) {
+                error_report("NFS Warning: Truncating NFS readahead"
+                             " size to %d", QEMU_NFS_MAX_READAHEAD_SIZE);
+                val = QEMU_NFS_MAX_READAHEAD_SIZE;
+            }
             nfs_set_readahead(client->context, val);
 #endif
         } else {
-- 
2.4.3