[PATCH 5.17 0833/1126] LSM: general protection fault in legacy_parse_param

Greg Kroah-Hartman
2022-04-05T09:27:18Z

From: Casey Schaufler <casey@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@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>
---
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 e9526f005f09..b7cf5cbfdc67 100644
--- a/security/security.c
+++ b/security/security.c
@@ -884,9 +884,22 @@ 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 b55f5efd3e0d..047c63f923b8 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2867,10 +2867,9 @@ 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