Xen devel - Mar 2012 - [PATCH] tapdisk2: initialize 'name' parameter of BLKTAP2_IOCTL_CREATE_DEVICE

This keeps the kernel driver from printing garbage.

Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/tools/blktap2/drivers/tapdisk-control.c
+++ b/tools/blktap2/drivers/tapdisk-control.c
@@ -462,6 +462,7 @@ tapdisk_control_open_image(struct tapdis
 
 	params.capacity = image.size;
 	params.sector_size = image.secsize;
+	strncpy(params.name, vbd->name, BLKTAP2_MAX_MESSAGE_LEN);
 
 	err = ioctl(vbd->ring.fd, BLKTAP2_IOCTL_CREATE_DEVICE, &params);
 	if (err && errno != EEXIST) {





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Jan Beulich writes ("[Xen-devel] [PATCH] tapdisk2: initialize
''name'' parameter of
BLKTAP2_IOCTL_CREATE_DEVICE"):
> This keeps the kernel driver from printing garbage.
...
> +	strncpy(params.name, vbd->name, BLKTAP2_MAX_MESSAGE_LEN);
I don''t think this is right.  As the FM for strncpy puts it:

 |        Warning: If there is no null byte among the first n bytes
 | of src, the string placed in dest will not be null-terminated.

An easy fix would be to memset params to 0 first.

Ian.

>>> On 13.03.12 at 16:53, Ian Jackson <Ian.Jackson@eu.citrix.com>
wrote:
> Jan Beulich writes ("[Xen-devel] [PATCH] tapdisk2: initialize
''name'' parameter
> of BLKTAP2_IOCTL_CREATE_DEVICE"):
>> This keeps the kernel driver from printing garbage.
> ...
>> +	strncpy(params.name, vbd->name, BLKTAP2_MAX_MESSAGE_LEN);
> 
> I don''t think this is right.  As the FM for strncpy puts it:
> 
>  |        Warning: If there is no null byte among the first n bytes
>  | of src, the string placed in dest will not be null-terminated.
That''s actually expected here - the kernel code needs to be careful
about no trailing NUL anyway.
> An easy fix would be to memset params to 0 first.
That would not help at all - if src is longer than available space, then
there still wouldn''t be a NUL in the end. On would additionally have to
subtract 1 from the size argument. But as said, all that is unnecessary.

Jan

Jan Beulich writes ("Re: [Xen-devel] [PATCH] tapdisk2: initialize
''name'' parameter of
BLKTAP2_IOCTL_CREATE_DEVICE"):
> >  |        Warning: If there is no null byte among the first n bytes
> >  | of src, the string placed in dest will not be null-terminated.
> 
> That''s actually expected here - the kernel code needs to be
careful
> about no trailing NUL anyway.
Oh, OK.
> > An easy fix would be to memset params to 0 first.
> 
> That would not help at all - if src is longer than available space, then
> there still wouldn''t be a NUL in the end. On would additionally
have to
> subtract 1 from the size argument. But as said, all that is unnecessary.
Yes, I realised that suggestion of mine was confused.

Ian.

Jan Beulich writes ("[Xen-devel] [PATCH] tapdisk2: initialize
''name'' parameter of
BLKTAP2_IOCTL_CREATE_DEVICE"):
> tapdisk2: initialize ''name'' parameter of
BLKTAP2_IOCTL_CREATE_DEVICE
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>