[PATCH 8/8] perf machine: Check snprintf truncation for guest kallsyms path

[Arnaldo Carvalho de Melo <acme@kernel.org>]

From: Arnaldo Carvalho de Melo <acme@redhat.com>

machines__create_guest_kernel_maps() builds the guest kallsyms path
with snprintf() without checking the return value.  A truncated path
could pass the access() check if a prefix directory happens to contain
a file named "kallsyms", leading to the wrong file being used for
symbol resolution.

Check for truncation and skip the directory.

Fixes: a1645ce12adb ("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>
---
 tools/perf/util/machine.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 48c4b963e8097f4a..f86b3b7df742e0c1 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -1269,9 +1269,14 @@ int machines__create_guest_kernel_maps(struct machines *machines)
 				free(namelist[i]);
 				continue;
 			}
-			snprintf(path, sizeof(path), "%s/%s/proc/kallsyms",
-				 symbol_conf.guestmount,
-				 namelist[i]->d_name);
+			if (snprintf(path, sizeof(path), "%s/%s/proc/kallsyms",
+				     symbol_conf.guestmount,
+				     namelist[i]->d_name) >= (int)sizeof(path)) {
+				pr_debug("Guest kallsyms path too long for %s. Skipping.\n",
+					 namelist[i]->d_name);
+				free(namelist[i]);
+				continue;
+			}
 			if (access(path, R_OK)) {
 				pr_debug("Can't access file %s\n", path);
 				free(namelist[i]);
-- 
2.55.0