[pulseaudio-discuss] [PATCH] Remove redundant check of directory permissions

[Alexander E. Patrakov]

Initially (in commit ef422fa4ae626e9638ca70d1c56f27e701dd69c2),
pa_make_secure_dir followed a simple principle: "make a directory, or,
if it exists, check that it is suitable". Later this evolved into "make
a directory, or, if it exists, ensure that it is suitable". But the
check remained.

The check is now neither sufficient nor necessary. On POSIX-compliant
systems, the fstat results being checked are actually post-conditions of
fchmod and fchown. And on systems implementing POSIX ACLs, fstat only
reflects a part of the information relevant to the security of the
directory permissions, so PulseAudio could accept an existing insecure
directory anyway.

Also, the check still fires on non-POSIX-compliant filesystems like CIFS.
As a user cannot do anything to fix it, just accept insecure permissions
in this case.
---
As this patch removes what used to be a security check, please double-check
it. Especially on platforms that provide only a subset of fstat, fchown and
fchmod.

If you think it is too risky, apply the alternative with the subject
"Better error messages for secure directory creation".

 src/pulsecore/core-util.c | 24 +++++-------------------
 1 file changed, 5 insertions(+), 19 deletions(-)

diff --git a/src/pulsecore/core-util.c b/src/pulsecore/core-util.c
index 0d9e354..f80fdea 100644
--- a/src/pulsecore/core-util.c
+++ b/src/pulsecore/core-util.c
@@ -343,30 +343,16 @@ again:
 #endif
 
 #ifdef HAVE_FCHMOD
-    (void) fchmod(fd, m);
+    if (fchmod(fd, m) < 0) {
+        pa_assert_se(pa_close(fd) >= 0);
+        goto fail;
+    };
 #endif
 
     pa_assert_se(pa_close(fd) >= 0);
 }
-#endif
-
-#ifdef HAVE_LSTAT
-    if (lstat(dir, &st) < 0)
-#else
-    if (stat(dir, &st) < 0)
-#endif
-        goto fail;
-
-#ifndef OS_IS_WIN32
-    if (!S_ISDIR(st.st_mode) ||
-        (st.st_uid != uid) ||
-        (st.st_gid != gid) ||
-        ((st.st_mode & 0777) != m)) {
-        errno = EACCES;
-        goto fail;
-    }
 #else
-    pa_log_warn("Secure directory creation not supported on Win32.");
+    pa_log_warn("Secure directory creation not supported on this platform.");
 #endif
 
     return 0;
-- 
1.9.2