diff options
authorTobias Stoeckmann <>2019-07-12 19:43:59 +0200
committerTobias Stoeckmann <>2019-07-12 19:43:59 +0200
commit2c38c9da3ea45d6c692314ad2e2f7213de2afaeb (patch)
parent2c6e4fbabf502840a5138c489e3ace16294a9a75 (diff)
Check stat for error before setting permissions.
When setting wallpapers without --no-fehbg option, a ~/.fehbg file is created. This file is set to be an executable for later re-use. Calling stat() without checking the return value can lead to issues. If the call fails, then s.st_mode is undefined and excessive permissions could be set to .fehbg, at worst even setuid/setgid bits for a world writable file. While adjusting this, I changed the code to use fstat() and fchmod() to avoid a further -- but very unlikely -- issue: race condition in form of TOCTOU. If the file ~/.fehsetbg is replaced by a symlink right before the chmod call, then a different file would be set executable + the default mode of the (newly created) file. I don't expect this to be a real world issue but changed this part "while at it" anyway for more robust code and a good example on how to handle files. Signed-off-by: Tobias Stoeckmann <>
1 files changed, 4 insertions, 3 deletions
diff --git a/src/wallpaper.c b/src/wallpaper.c
index 9df259f..96b4f90 100644
--- a/src/wallpaper.c
+++ b/src/wallpaper.c
@@ -452,6 +452,7 @@ void feh_wm_set_bg(char *fil, Imlib_Image im, int centered, int scaled,
home = getenv("HOME");
if (home) {
FILE *fp;
+ int fd;
char *path;
char *absolute_path;
struct stat s;
@@ -519,11 +520,11 @@ void feh_wm_set_bg(char *fil, Imlib_Image im, int centered, int scaled,
fputc('\n', fp);
- fclose(fp);
- stat(path, &s);
- if (chmod(path, s.st_mode | S_IXUSR | S_IXGRP) != 0) {
+ fd = fileno(fp);
+ if (fstat(fd, &s) != 0 || fchmod(fd, s.st_mode | S_IXUSR | S_IXGRP) != 0) {
weprintf("Can't set %s as executable", path);
+ fclose(fp);