Commit 2c38c9da authored by Tobias Stoeckmann's avatar Tobias Stoeckmann
Browse files

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: default avatarTobias Stoeckmann <tobias@stoeckmann.org>
parent 2c6e4fba

src/wallpaper.c

+4 −3
Original line number Diff line number Diff line
@@ -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, 
						free(absolute_path);

					}

					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);

				}

				free(path);

			}