strip_exif support for the OpenBSD sandbox

Change the strip_exif logic to work with the already existing OpenBSD
sandbox and allow ffmpeg and mogrify to be executed.

The previous strip_exif implementation relied on system(3), effectively
starting "/bin/sh" and executing the required tool within a shell
session. Making this work in the sandbox would require to allow
executing "/bin/sh", rendering the sandbox useless.

Thus, the code now starts determining the absolute path of the tools -
unless they are given as ffmpeg_path or mogrify_path - and allowing them
to be executed via unveil(2). Then, instead of the system(3) call, the
good old fork(2) and execve(2) dance is performed.

The sbox_enter code was made aware of strip_exif, which resulted in a
pledge(2) violation before when disable_email_notifications was set to
false. Furthermore, the detected paths of the tools are now allowed.

1 files changed, 8 insertions, 1 deletions

diff --git a/sandbox.c b/sandbox.c
index c6cfdcb..15e4622 100644
--- a/sandbox.c
+++ b/sandbox.c
@@ -13,6 +13,8 @@ void sbox_enter(const char *basedir)
         return;
     }
 
+    const xs_val *strip_exif = xs_dict_get(srv_config, "strip_exif");
+
     int smail;
     const char *url = xs_dict_get(srv_config, "smtp_url");
 
@@ -33,6 +35,11 @@ void sbox_enter(const char *basedir)
     if (*address == '/')
         unveil(address, "rwc");
 
+    if (strip_exif) {
+        unveil(xs_dict_get(srv_config, "ffmpeg_path"), "x");
+        unveil(xs_dict_get(srv_config, "mogrify_path"), "x");
+    }
+
     if (smail)
         unveil("/usr/sbin/sendmail",   "x");
 
@@ -45,7 +52,7 @@ void sbox_enter(const char *basedir)
     if (*address == '/')
         p = xs_str_cat(p, " unix");
 
-    if (smail)
+    if (smail || strip_exif)
         p = xs_str_cat(p, " exec");
 
     pledge(p, NULL);