Re: [PATCH] net/ceph/osdmap.c: fix undefined behavior when using snprintf()
On 01/22/2013 01:20 PM, Cong Ding wrote:
The variable str is used as both the source and destination in function
snprintf(), which is undefined behavior based on C11. The original description
in C11 is:
If copying takes place between objects that
overlap, the behavior is undefined.
Yes, this was an ill-advised thing to do in this function.
In fact, the only place this function is used (in osdmap_show()),
the non-static buffer was not initialized before the call. (It
might happen to work because the same stack space was getting
reused each time through the loop. Ew!)
This is just an awful couple of functions.
And, the function of ceph_osdmap_state_str() is to return the osdmap state, so
it should return doesn't exist when all the conditions are not satisfied. I
fix it in this patch.
Based on C11, snprintf() does nothing if n==0:
If n is zero, nothing is written, and s may be a
null pointer. Otherwise, output characters beyond
the n-1st are discarded rather than being written to
the array, and a null character is written at the
end of the characters actually written into the
array.
so I remove the unnecessary check of len (because it is not a busy path and
saves a few lines of code).
True. But since you know it's not going to do anything why
not only make the call if len is non-zero? I.e.:
else if (len)
snprintf(str, len, doesn't exist);
With your permission I'll make this change and will commit
this for you. OK?
Signed-off-by: Cong Ding ding...@gmail.com
Reviewed-by: Alex Elder el...@inktank.com
---
net/ceph/osdmap.c | 27 ---
1 file changed, 8 insertions(+), 19 deletions(-)
diff --git a/net/ceph/osdmap.c b/net/ceph/osdmap.c
index de73214..3131a99d3 100644
--- a/net/ceph/osdmap.c
+++ b/net/ceph/osdmap.c
@@ -13,26 +13,15 @@
char *ceph_osdmap_state_str(char *str, int len, int state)
{
- int flag = 0;
-
- if (!len)
- goto done;
-
- *str = '\0';
- if (state) {
- if (state CEPH_OSD_EXISTS) {
- snprintf(str, len, exists);
- flag = 1;
- }
- if (state CEPH_OSD_UP) {
- snprintf(str, len, %s%s%s, str, (flag ? , : ),
- up);
- flag = 1;
- }
- } else {
+ if ((state CEPH_OSD_EXISTS) (state CEPH_OSD_UP))
+ snprintf(str, len, exists, up);
+ else if (state CEPH_OSD_EXISTS)
+ snprintf(str, len, exists);
+ else if (state CEPH_OSD_UP)
+ snprintf(str, len, up);
+ else
snprintf(str, len, doesn't exist);
- }
-done:
+
return str;
}
--
To unsubscribe from this list: send the line unsubscribe ceph-devel in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] net/ceph/osdmap.c: fix undefined behavior when using snprintf()
On Wed, Jan 23, 2013 at 10:48:07AM -0600, Alex Elder wrote:
On 01/22/2013 01:20 PM, Cong Ding wrote:
The variable str is used as both the source and destination in function
snprintf(), which is undefined behavior based on C11. The original
description
in C11 is:
If copying takes place between objects that
overlap, the behavior is undefined.
Yes, this was an ill-advised thing to do in this function.
In fact, the only place this function is used (in osdmap_show()),
the non-static buffer was not initialized before the call. (It
might happen to work because the same stack space was getting
reused each time through the loop. Ew!)
This is just an awful couple of functions.
And, the function of ceph_osdmap_state_str() is to return the osdmap state,
so
it should return doesn't exist when all the conditions are not satisfied.
I
fix it in this patch.
Based on C11, snprintf() does nothing if n==0:
If n is zero, nothing is written, and s may be a
null pointer. Otherwise, output characters beyond
the n-1st are discarded rather than being written to
the array, and a null character is written at the
end of the characters actually written into the
array.
so I remove the unnecessary check of len (because it is not a busy path and
saves a few lines of code).
True. But since you know it's not going to do anything why
not only make the call if len is non-zero? I.e.:
else if (len)
snprintf(str, len, doesn't exist);
With your permission I'll make this change and will commit
this for you. OK?
It's fine, thanks. But I think it's better to check len in the beginning
because other conditions also call snprintf with parameter len. Like this:
if (!len)
return str;
if ((state CEPH_OSD_EXISTS) (state CEPH_OSD_UP))
snprintf(str, len, exists, up);
else if (state CEPH_OSD_EXISTS)
snprintf(str, len, exists);
else if (state CEPH_OSD_UP)
snprintf(str, len, up);
else
snprintf(str, len, doesn't exist);
return str;
or like this:
if (len) {
if ((state CEPH_OSD_EXISTS) (state CEPH_OSD_UP))
snprintf(str, len, exists, up);
else if (state CEPH_OSD_EXISTS)
snprintf(str, len, exists);
else if (state CEPH_OSD_UP)
snprintf(str, len, up);
else
snprintf(str, len, doesn't exist);
}
return str;
Thanks,
- cong
--
To unsubscribe from this list: send the line unsubscribe ceph-devel in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] net/ceph/osdmap.c: fix undefined behavior when using snprintf()
On 01/23/2013 11:41 AM, Cong Ding wrote:
On Wed, Jan 23, 2013 at 10:48:07AM -0600, Alex Elder wrote:
On 01/22/2013 01:20 PM, Cong Ding wrote:
The variable str is used as both the source and destination in function
snprintf(), which is undefined behavior based on C11. The original
description
in C11 is:
If copying takes place between objects that
overlap, the behavior is undefined.
Yes, this was an ill-advised thing to do in this function.
In fact, the only place this function is used (in osdmap_show()),
the non-static buffer was not initialized before the call. (It
might happen to work because the same stack space was getting
reused each time through the loop. Ew!)
This is just an awful couple of functions.
And, the function of ceph_osdmap_state_str() is to return the osdmap state,
so
it should return doesn't exist when all the conditions are not satisfied.
I
fix it in this patch.
Based on C11, snprintf() does nothing if n==0:
If n is zero, nothing is written, and s may be a
null pointer. Otherwise, output characters beyond
the n-1st are discarded rather than being written to
the array, and a null character is written at the
end of the characters actually written into the
array.
so I remove the unnecessary check of len (because it is not a busy path and
saves a few lines of code).
True. But since you know it's not going to do anything why
not only make the call if len is non-zero? I.e.:
else if (len)
snprintf(str, len, doesn't exist);
With your permission I'll make this change and will commit
this for you. OK?
It's fine, thanks. But I think it's better to check len in the beginning
because other conditions also call snprintf with parameter len. Like this:
OK. I'll do this. Thank you. -Alex
if (!len)
return str;
if ((state CEPH_OSD_EXISTS) (state CEPH_OSD_UP))
snprintf(str, len, exists, up);
else if (state CEPH_OSD_EXISTS)
snprintf(str, len, exists);
else if (state CEPH_OSD_UP)
snprintf(str, len, up);
else
snprintf(str, len, doesn't exist);
return str;
or like this:
if (len) {
if ((state CEPH_OSD_EXISTS) (state CEPH_OSD_UP))
snprintf(str, len, exists, up);
else if (state CEPH_OSD_EXISTS)
snprintf(str, len, exists);
else if (state CEPH_OSD_UP)
snprintf(str, len, up);
else
snprintf(str, len, doesn't exist);
}
return str;
Thanks,
- cong
--
To unsubscribe from this list: send the line unsubscribe ceph-devel in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
