Messages in this thread | | | Subject | Re: [PATCH] perf cpumap: Use scnprintf instead of snprintf | From | Christophe JAILLET <> | Date | Mon, 23 Mar 2020 13:08:47 +0100 |
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Le 23/03/2020 à 12:03, Dan Carpenter a écrit : > On Sun, Mar 22, 2020 at 06:25:23PM +0100, Christophe JAILLET wrote: >> 'scnprintf' returns the number of characters written in the output buffer >> excluding the trailing '\0', instead of the number of characters which >> would be generated for the given input. >> >> Both function return a number of characters, excluding the trailing '\0'. >> So comparaison to check if it overflows, should be done against max_size-1. >> Comparaison against max_size can never match. >> >> Fixes: 7780c25bae59f ("perf tools: Allow ability to map cpus to nodes easily") >> Fixes: a24020e6b7cf6 ("perf tools: Change cpu_map__fprintf output") >> Fixes: 92a7e1278005b ("perf cpumap: Add cpu__max_present_cpu()") >> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr> >> --- >> tools/perf/util/cpumap.c | 39 ++++++++++++++++++++------------------- >> 1 file changed, 20 insertions(+), 19 deletions(-) >> >> diff --git a/tools/perf/util/cpumap.c b/tools/perf/util/cpumap.c >> index 983b7388f22b..b87e7ef4d130 100644 >> --- a/tools/perf/util/cpumap.c >> +++ b/tools/perf/util/cpumap.c >> @@ -316,8 +316,8 @@ static void set_max_cpu_num(void) >> goto out; >> >> /* get the highest possible cpu number for a sparse allocation */ >> - ret = snprintf(path, PATH_MAX, "%s/devices/system/cpu/possible", mnt); >> - if (ret == PATH_MAX) { >> + ret = scnprintf(path, PATH_MAX, "%s/devices/system/cpu/possible", mnt); >> + if (ret == PATH_MAX-1) { > This should be a static analysis warning. > > But isn't this stuff userspace? I can't figure out how to compile it on > Debian so I'm not sure. There is no scnprintf() in user space. > > regards, > dan carpenter
I compiled it with:
make tools/perf
the cpumap.o is generated and if I introduce an error, 'scn<SPACE>printf' for example, gcc triggers a built error.
I though it was enough to validate the patch, before sending it.
Anyway, keeping 'snprintf' could be better to check for the overflow, but 'if (ret == PATH_MAX)' should be turned in 'if (ret >= PATH_MAX)'. If agreed, I can send a V2.
CJ
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