[PATCH] LSM: general protection fault in legacy_parse_param

Casey Schaufler
2021-10-11T22:40:32Z

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.

Reported-by: syzbot+d1e3b1d92d25abf97943@syzkaller.appspotmail.com
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
---
security/security.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/security/security.c b/security/security.c
index 09533cbb7221..3cf0faaf1c5b 100644
--- a/security/security.c
+++ b/security/security.c
@@ -885,7 +885,19 @@ int security_fs_context_dup(struct fs_context *fc, struct fs_context *src_fc)

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)