perf machine: Use snprintf() for guestmount path construction

machines__findnew() and machines__create_guest_kernel_maps() use
sprintf() to build paths by prepending symbol_conf.guestmount.
Both write into PATH_MAX stack buffers, but guestmount comes from
user configuration and is not length-checked.  A guestmount path
at or near PATH_MAX causes a stack buffer overflow.

Switch to snprintf() with sizeof() to prevent overflow.  The
subsequent access()/fopen() calls will fail on a truncated path.

Fixes: a1645ce12adb6c9c ("perf: 'perf kvm' tool for monitoring guest performance from host")
Reported-by: sashiko-bot <sashiko-bot@kernel.org>
Cc: Zhang, Yanmin <yanmin_zhang@linux.intel.com>
Assisted-by: Claude:claude-opus-4.6
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 9329d319bd0336991659c2ae93ab6747707444ee..0d2ebf6a84bcf8808b3a56a24756c8a7163b7a67 100644 (file)
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -333,7 +333,7 @@ struct machine *machines__findnew(struct machines *machines, pid_t pid)
        if ((pid != HOST_KERNEL_ID) &&
            (pid != DEFAULT_GUEST_KERNEL_ID) &&
            (symbol_conf.guestmount)) {
-               sprintf(path, "%s/%d", symbol_conf.guestmount, pid);
+               snprintf(path, sizeof(path), "%s/%d", symbol_conf.guestmount, pid);
                if (access(path, R_OK)) {
                        static struct strlist *seen;
 
@@ -1260,9 +1260,9 @@ int machines__create_guest_kernel_maps(struct machines *machines)
                                         namelist[i]->d_name);
                                continue;
                        }
-                       sprintf(path, "%s/%s/proc/kallsyms",
-                               symbol_conf.guestmount,
-                               namelist[i]->d_name);
+                       snprintf(path, sizeof(path), "%s/%s/proc/kallsyms",
+                                symbol_conf.guestmount,
+                                namelist[i]->d_name);
                        ret = access(path, R_OK);
                        if (ret) {
                                pr_debug("Can't access file %s\n", path);