[Qemu-devel] [PATCH] block/nfs: limit maximum readahead size to 1MB

[Qemu-devel] [PATCH] block/nfs: limit maximum readahead size to 1MB

[Peter Lieven]

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: qemu-stable@nongnu.org
Signed-off-by: Peter Lieven <pl@kamp.de>
---
 block/nfs.c |    7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/block/nfs.c b/block/nfs.c
index 43d48ae..4fb1937 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;
@@ -351,6 +353,11 @@ 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 {
-- 
1.7.9.5

Re: [Qemu-devel] [Qemu-block] [PATCH] block/nfs: limit maximum readahead size to 1MB

[Stefan Hajnoczi]

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On Fri, Jun 26, 2015 at 01:14:01PM +0200, Peter Lieven wrote:
> 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: qemu-stable@nongnu.org
> Signed-off-by: Peter Lieven <pl@kamp.de>
> ---
>  block/nfs.c |    7 +++++++
>  1 file changed, 7 insertions(+)

Thanks, applied to my block tree:
https://github.com/stefanha/qemu/commits/block

Stefan

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