[systemd-devel] [PATCH] fileio: quote more shell characters in envfiles

[Mantas Mikulėnas]

Turns out, making strings shell-proof is harder than expected:

    # machinectl set-hostname "foo|poweroff" && . /etc/machine-info

(This could be simplified by quoting *and* escaping all characters,
which is harmless in shell but unnecessary.)
---
 src/shared/fileio.c | 4 ++--
 src/shared/util.h   | 6 ++++++
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/shared/fileio.c b/src/shared/fileio.c
index b0ab780..cbb40c2 100644
--- a/src/shared/fileio.c
+++ b/src/shared/fileio.c
@@ -738,11 +738,11 @@ static void write_env_var(FILE *f, const char *v) {
         p++;
         fwrite(v, 1, p-v, f);
 
-        if (string_has_cc(p, NULL) || chars_intersect(p, WHITESPACE "\'\"\\`$")) {
+        if (string_has_cc(p, NULL) || chars_intersect(p, WHITESPACE SHELL_NEED_QUOTES)) {
                 fputc('\"', f);
 
                 for (; *p; p++) {
-                        if (strchr("\'\"\\`$", *p))
+                        if (strchr(SHELL_NEED_ESCAPE, *p))
                                 fputc('\\', f);
 
                         fputc(*p, f);
diff --git a/src/shared/util.h b/src/shared/util.h
index c5eadc9..b3187a9 100644
--- a/src/shared/util.h
+++ b/src/shared/util.h
@@ -93,6 +93,12 @@
 #define COMMENTS   "#;"
 #define GLOB_CHARS "*?["
 
+/* What characters are special in the shell? */
+/* must be escaped outside and inside double-quotes */
+#define SHELL_NEED_ESCAPE "\"\\`$"
+/* can be escaped or double-quoted */
+#define SHELL_NEED_QUOTES SHELL_NEED_ESCAPE GLOB_CHARS "'()<>|&;"
+
 #define FORMAT_BYTES_MAX 8
 
 #define ANSI_HIGHLIGHT_ON "\x1B[1;39m"
-- 
2.0.1