Le 25/03/2020 à 15:52, Chuck Lever a écrit :
Hi Christophe,
On Mar 25, 2020, at 3:04 AM, Christophe JAILLET <christophe.jaillet@xxxxxxxxxx> wrote:
Using 'snprintf' is safer than 'sprintf' because it can avoid a buffer
overflow.
That's true as a general statement, but how likely is such an
overflow to occur here?
I guess, that it us unlikely and that the 80 chars buffer is big enough.
That is the exact reason of why I've proposed 2 patches. The first one
could happen in RL. The 2nd is more like a clean-up and is less
relevant, IMHO.
The return value can also be used to avoid a strlen a call.
That's also true of sprintf, isn't it?
Sure.
Finally, we know where we need to copy and the length to copy, so, we
can save a few cycles by rearraging the code and using a memcpy instead of
a strcat.
I would be OK with squashing these two patches together. I don't
see the need to keep the two changes separated.
NP, I can resend as a V2 with your comments.
As said above, the first fixes something that could, IMHO, happen and
the 2nd is more a matter of taste and a clean-up.
Signed-off-by: Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>
---
This patch should have no functionnal change.
We could go further, use scnprintf and write directly in the destination
buffer. However, this could lead to a truncated last line.
That's exactly what this function is trying to avoid. As part of any
change in this area, it would be good to replace the current block
comment before this function with a Doxygen-format comment that
documents that goal.
I'll take care of it.
---
net/sunrpc/svc_xprt.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index df39e7b8b06c..6df861650040 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -118,12 +118,12 @@ int svc_print_xprts(char *buf, int maxlen)
list_for_each_entry(xcl, &svc_xprt_class_list, xcl_list) {
int slen;
- sprintf(tmpstr, "%s %d\n", xcl->xcl_name, xcl->xcl_max_payload);
- slen = strlen(tmpstr);
- if (len + slen >= maxlen)
+ slen = snprintf(tmpstr, sizeof(tmpstr), "%s %d\n",
+ xcl->xcl_name, xcl->xcl_max_payload);
+ if (slen >= sizeof(tmpstr) || len + slen >= maxlen)
break;
+ memcpy(buf + len, tmpstr, slen + 1);
len += slen;
- strcat(buf, tmpstr);
IMO replacing the strcat makes the code harder to read, and this
is certainly not a performance path. Can you drop that part of the
patch?
Ok
}
spin_unlock(&svc_xprt_class_lock);
--
2.20.1
--
Chuck Lever
