LSM: general protection fault in legacy_parse_param

BugLink: https://bugs.launchpad.net/bugs/1969110
[ Upstream commit ecff30575b5ad0eda149aadad247b7f75411fd47 ]

The usual LSM hook "bail on fail" scheme doesn't work for cases where
a security module may return an error code indicating that it does not
recognize an input.  In this particular case Smack sees a mount option
that it recognizes, and returns 0. A call to a BPF hook follows, which
returns -ENOPARAM, which confuses the caller because Smack has processed
its data.

The SELinux hook incorrectly returns 1 on success. There was a time
when this was correct, however the current expectation is that it
return 0 on success. This is repaired.

Reported-by: syzbot+d1e3b1d92d25abf97943@syzkaller.appspotmail.com
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
Acked-by: James Morris <jamorris@linux.microsoft.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
(cherry picked from commit f3f93a1aaafc3032e0a9655fb43deccfb3e953a3)
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>

diff --git a/security/security.c b/security/security.c
index 07a32ed3fc9f55ca99291f3d81be2d98588cd5b5..b153316c234ef33783996759c2c7e2d88b4e9ec3 100644 (file)
--- a/security/security.c
+++ b/security/security.c
@@ -1054,9 +1054,22 @@ int security_fs_context_dup(struct fs_context *fc, struct fs_context *src_fc)
        return call_int_hook(fs_context_dup, 0, fc, src_fc);
 }
 
-int security_fs_context_parse_param(struct fs_context *fc, struct fs_parameter *param)
+int security_fs_context_parse_param(struct fs_context *fc,
+                                   struct fs_parameter *param)
 {
-       return call_int_hook(fs_context_parse_param, -ENOPARAM, fc, param);
+       struct security_hook_list *hp;
+       int trc;
+       int rc = -ENOPARAM;
+
+       hlist_for_each_entry(hp, &security_hook_heads.fs_context_parse_param,
+                            list) {
+               trc = hp->hook.fs_context_parse_param(fc, param);
+               if (trc == 0)
+                       rc = 0;
+               else if (trc != -ENOPARAM)
+                       return trc;
+       }
+       return rc;
 }
 
 int security_sb_alloc(struct super_block *sb)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index bbcbecdb1f1c6ec6fd6cfb1c1aa8c613dbfa93da..9c38479d57d2c890dd11120c66cd48e6f06ca6b6 100644 (file)
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2915,10 +2915,9 @@ static int selinux_fs_context_parse_param(struct fs_context *fc,
                return opt;
 
        rc = selinux_add_opt(opt, param->string, &fc->security);
-       if (!rc) {
+       if (!rc)
                param->string = NULL;
-               rc = 1;
-       }
+
        return rc;
 }