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[Qemu-devel] [PATCH v4 11/11] nbd: Avoid magic number for NBD max name s
From: |
Eric Blake |
Subject: |
[Qemu-devel] [PATCH v4 11/11] nbd: Avoid magic number for NBD max name size |
Date: |
Wed, 11 May 2016 16:39:44 -0600 |
Declare a constant and use that when determining if an export
name fits within the constraints we are willing to support.
Note that upstream NBD recently documented that clients MUST
support export names of 256 bytes (not including trailing NUL),
and SHOULD support names up to 4096 bytes. 4096 is a bit big
(we would lose benefits of stack-allocation of a name array),
and we already have other limits in place (for example, qcow2
snapshot names are clamped around 1024). So for now, just
stick to the required minimum, as that's easier to audit than
a full-scale support for larger names.
Signed-off-by: Eric Blake <address@hidden>
---
v3: enlarge the limit, and document choice of new value
---
include/block/nbd.h | 6 ++++++
nbd/client.c | 2 +-
nbd/server.c | 4 ++--
3 files changed, 9 insertions(+), 3 deletions(-)
diff --git a/include/block/nbd.h b/include/block/nbd.h
index 3e2d76b..2c753cc 100644
--- a/include/block/nbd.h
+++ b/include/block/nbd.h
@@ -76,6 +76,12 @@ enum {
/* Maximum size of a single READ/WRITE data buffer */
#define NBD_MAX_BUFFER_SIZE (32 * 1024 * 1024)
+/* Maximum size of an export name. The NBD spec requires 256 and
+ * suggests that servers support up to 4096, but we stick to only the
+ * required size so that we can stack-allocate the names, and because
+ * going larger would require an audit of more code to make sure we
+ * aren't overflowing some other buffer. */
+#define NBD_MAX_NAME_SIZE 256
ssize_t nbd_wr_syncv(QIOChannel *ioc,
struct iovec *iov,
diff --git a/nbd/client.c b/nbd/client.c
index 4659df3..b700100 100644
--- a/nbd/client.c
+++ b/nbd/client.c
@@ -210,7 +210,7 @@ static int nbd_receive_list(QIOChannel *ioc, char **name,
Error **errp)
error_setg(errp, "incorrect option name length");
return -1;
}
- if (namelen > 255) {
+ if (namelen > NBD_MAX_NAME_SIZE) {
error_setg(errp, "export name length too long %" PRIu32, namelen);
return -1;
}
diff --git a/nbd/server.c b/nbd/server.c
index b8de8aa..7ffa168 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -296,13 +296,13 @@ static int nbd_negotiate_handle_list(NBDClient *client,
uint32_t length)
static int nbd_negotiate_handle_export_name(NBDClient *client, uint32_t length)
{
int rc = -EINVAL;
- char name[256];
+ char name[NBD_MAX_NAME_SIZE + 1];
/* Client sends:
[20 .. xx] export name (length bytes)
*/
TRACE("Checking length");
- if (length > 255) {
+ if (length >= sizeof(name)) {
LOG("Bad length received");
goto fail;
}
--
2.5.5
- [Qemu-devel] [PATCH v4 00/11] nbd: tighter protocol compliance, Eric Blake, 2016/05/11
- [Qemu-devel] [PATCH v4 01/11] nbd: Use BDRV_REQ_FUA for better FUA where supported, Eric Blake, 2016/05/11
- [Qemu-devel] [PATCH v4 10/11] nbd: Detect servers that send unexpected error values, Eric Blake, 2016/05/11
- [Qemu-devel] [PATCH v4 11/11] nbd: Avoid magic number for NBD max name size,
Eric Blake <=
- [Qemu-devel] [PATCH v4 07/11] nbd: Clean up ioctl handling of qemu-nbd -c, Eric Blake, 2016/05/11
- [Qemu-devel] [PATCH v4 06/11] nbd: Group all Linux-specific ioctl code in one place, Eric Blake, 2016/05/11
- [Qemu-devel] [PATCH v4 02/11] nbd: More debug typo fixes, use correct formats, Eric Blake, 2016/05/11
- [Qemu-devel] [PATCH v4 05/11] nbd: Reject unknown request flags, Eric Blake, 2016/05/11
- [Qemu-devel] [PATCH v4 08/11] nbd: Limit nbdflags to 16 bits, Eric Blake, 2016/05/11
- [Qemu-devel] [PATCH v4 09/11] nbd: Add qemu-nbd -D for human-readable description, Eric Blake, 2016/05/11
- [Qemu-devel] [PATCH v4 03/11] nbd: Quit server after any write error, Eric Blake, 2016/05/11