The code checks existance of a command (halt/poweroff/reboot) by using stat(2) and immediately checking for S_ISLNK() on the returned stat struct. This check will never be true, because stat(2) always follows symbolic links and hence will either return ENOENT (in case of dangling symlink) or the properties for the final target file. It is lstat(2) which might return information about the symlink itself. However, even there, we want to check the final file properties, not the first symlink.
This check - S_ISLNK - is harmful but useless in this case. However, it is confusing and it helps the wrong usage of stat(2) to spread, so it is better to remove it. Additionally, the code would better to check for the executable bits of the final file, not check if it's a regular file - it's sort of dubious to have anything but regular files in /sbin/. But a POSIX system provides another command which suits the purpose perfectly: it is access(2). And it is so simple that it's not necessary to create a separate function when usin it. Replace stat(2) with access(X_OK) to check for file existance in qga/commands-posix.c Fixes: c5b4afd4d56e "qga: Support guest shutdown of BusyBox-based systems" Signed-off-by: Michael Tokarev <[email protected]> --- qga/commands-posix.c | 12 +++--------- 1 file changed, 3 insertions(+), 9 deletions(-) diff --git a/qga/commands-posix.c b/qga/commands-posix.c index c7059857e4..0f4d6d96cc 100644 --- a/qga/commands-posix.c +++ b/qga/commands-posix.c @@ -213,12 +213,6 @@ out: return retcode; } -static bool file_exists(const char *path) -{ - struct stat st; - return stat(path, &st) == 0 && (S_ISREG(st.st_mode) || S_ISLNK(st.st_mode)); -} - #define POWEROFF_CMD_PATH "/sbin/poweroff" #define HALT_CMD_PATH "/sbin/halt" #define REBOOT_CMD_PATH "/sbin/reboot" @@ -245,17 +239,17 @@ void qmp_guest_shutdown(const char *mode, Error **errp) slog("guest-shutdown called, mode: %s", mode); if (!mode || strcmp(mode, "powerdown") == 0) { - if (file_exists(POWEROFF_CMD_PATH)) { + if (access(POWEROFF_CMD_PATH, X_OK)) { shutdown_cmd = POWEROFF_CMD_PATH; } shutdown_flag = powerdown_flag; } else if (strcmp(mode, "halt") == 0) { - if (file_exists(HALT_CMD_PATH)) { + if (access(HALT_CMD_PATH, X_OK)) { shutdown_cmd = HALT_CMD_PATH; } shutdown_flag = halt_flag; } else if (strcmp(mode, "reboot") == 0) { - if (file_exists(REBOOT_CMD_PATH)) { + if (access(REBOOT_CMD_PATH, X_OK)) { shutdown_cmd = REBOOT_CMD_PATH; } shutdown_flag = reboot_flag; -- 2.47.3
