[PATCH AUTOSEL 5.4 01/16] LSM: general protection fault in legacy_parse_param

[Sasha Levin]

From: Casey Schaufler <casey at schaufler-ca.com>

[ 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 at syzkaller.appspotmail.com
Signed-off-by: Casey Schaufler <casey at schaufler-ca.com>
Acked-by: James Morris <jamorris at linux.microsoft.com>
Signed-off-by: Paul Moore <paul at paul-moore.com>
Signed-off-by: Sasha Levin <sashal at kernel.org>
---
 security/security.c      | 17 +++++++++++++++--
 security/selinux/hooks.c |  5 ++---
 2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/security/security.c b/security/security.c
index c34ec4c7d98c..f633717311a3 100644
--- a/security/security.c
+++ b/security/security.c
@@ -802,9 +802,22 @@ 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 56418cf72069..d9f15c84aab7 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2855,10 +2855,9 @@ 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;
 }
 
-- 
2.34.1