[PATCH v2 1/3] tools subcmd: Tighten the filename size in check_if_command_finished

[Ian Rogers <irogers@google.com>]

FILENAME_MAX is often PATH_MAX (4kb), far more than needed for the
/proc path. Make the buffer size sufficient for the maximum integer
plus "/proc/" and "/status" with a '\0' terminator.

Fixes: 5ce42b5de461 ("tools subcmd: Add non-waitpid check_if_command_finished()")
Signed-off-by: Ian Rogers <irogers@google.com>
---
v2: Fix precedence issue reported by the kernel test robot.
---
 tools/lib/subcmd/run-command.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/tools/lib/subcmd/run-command.c b/tools/lib/subcmd/run-command.c
index 0a764c25c384..b7510f83209a 100644
--- a/tools/lib/subcmd/run-command.c
+++ b/tools/lib/subcmd/run-command.c
@@ -5,6 +5,7 @@
 #include <ctype.h>
 #include <fcntl.h>
 #include <string.h>
+#include <linux/compiler.h>
 #include <linux/string.h>
 #include <errno.h>
 #include <sys/wait.h>
@@ -216,10 +217,20 @@ static int wait_or_whine(struct child_process *cmd, bool block)
 	return result;
 }
 
+/*
+ * Conservative estimate of number of characaters needed to hold an a decoded
+ * integer, assume each 3 bits needs a character byte and plus a possible sign
+ * character.
+ */
+#ifndef is_signed_type
+#define is_signed_type(type) (((type)(-1)) < (type)1)
+#endif
+#define MAX_STRLEN_TYPE(type) (sizeof(type) * 8 / 3 + (is_signed_type(type) ? 1 : 0))
+
 int check_if_command_finished(struct child_process *cmd)
 {
 #ifdef __linux__
-	char filename[FILENAME_MAX + 12];
+	char filename[6 + MAX_STRLEN_TYPE(typeof(cmd->pid)) + 7 + 1];
 	char status_line[256];
 	FILE *status_file;
 
@@ -227,7 +238,7 @@ int check_if_command_finished(struct child_process *cmd)
 	 * Check by reading /proc/<pid>/status as calling waitpid causes
 	 * stdout/stderr to be closed and data lost.
 	 */
-	sprintf(filename, "/proc/%d/status", cmd->pid);
+	sprintf(filename, "/proc/%u/status", cmd->pid);
 	status_file = fopen(filename, "r");
 	if (status_file == NULL) {
 		/* Open failed assume finish_command was called. */
-- 
2.50.0.727.gbf7dc18ff4-goog