[RFC v2 07/10] landlock: Add errno check

[MickaÃl SalaÃn]

Add a max errno value.

This is not strictly needed but should improve reliability.

Signed-off-by: MickaÃl SalaÃn <mic@xxxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Serge E. Hallyn <serge@xxxxxxxxxx>
Cc: James Morris <james.l.morris@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
---
 include/uapi/asm-generic/errno-base.h | 1 +
 security/landlock/lsm.c               | 6 +++---
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/uapi/asm-generic/errno-base.h b/include/uapi/asm-generic/errno-base.h
index 65115978510f..43407a403e72 100644
--- a/include/uapi/asm-generic/errno-base.h
+++ b/include/uapi/asm-generic/errno-base.h
@@ -35,5 +35,6 @@
 #define	EPIPE		32	/* Broken pipe */
 #define	EDOM		33	/* Math argument out of domain of func */
 #define	ERANGE		34	/* Math result not representable */
+#define	_ERRNO_LAST	ERANGE
 
 #endif
diff --git a/security/landlock/lsm.c b/security/landlock/lsm.c
index aa9d4a64826e..322309068066 100644
--- a/security/landlock/lsm.c
+++ b/security/landlock/lsm.c
@@ -11,7 +11,6 @@
 #include <asm/current.h>
 #include <linux/bpf.h> /* enum bpf_reg_type, struct landlock_data */
 #include <linux/cred.h>
-#include <linux/err.h> /* MAX_ERRNO */
 #include <linux/filter.h> /* struct bpf_prog, BPF_PROG_RUN() */
 #include <linux/kernel.h> /* FIELD_SIZEOF() */
 #include <linux/lsm_hooks.h>
@@ -104,8 +103,9 @@ static int landlock_run_prog(__u64 args[6])
 				}
 			}
 			if (!ret) {
-				if (cur_ret > MAX_ERRNO)
-					ret = MAX_ERRNO;
+				/* check errno to not mess with kernel code */
+				if (cur_ret > _ERRNO_LAST)
+					ret = EPERM;
 				else
 					ret = cur_ret;
 			}
-- 
2.8.1