[PATCH] SELinux: Introduce security_file_ioctl_compat hook

[Alfred Piccioni <alpic@google.com>]

Some ioctl commands do not require ioctl permission, but are routed to
other permissions such as FILE_GETATTR or FILE_SETATTR. This routing is
done by comparing the ioctl cmd to a set of 64-bit flags (FS_IOC_*).

However, if a 32-bit process is running on a 64-bit kernel, it emmits
32-bit flags (FS_IOC32_*) for certain ioctl operations. These flags are
being checked erroneously, which leads to these ioctl operations being
routed to the ioctl permission, rather than the correct file
permissions.

This was also noted in a RED-PEN finding from a while back -
"/* RED-PEN how should LSM module know it's handling 32bit? */".

This patch introduces a new hook, security_file_ioctl_compat, that
replaces security_file_ioctl if the CONFIG_COMPAT flag is on. All
current LSMs have been changed to hook into the compat flag.

Reviewing the three places where we are currently using
security_file_ioctl, it appears that only SELinux needs a dedicated
compat change; TOMOYO and SMACK appear to be functional without any
change.

Fixes: 0b24dcb7f2f7 ("Revert "selinux: simplify ioctl checking"")
Signed-off-by: Alfred Piccioni <alpic@google.com>
Cc: stable@vger.kernel.org
---
 fs/ioctl.c                    |  3 +--
 fs/overlayfs/inode.c          |  4 ++++
 include/linux/lsm_hook_defs.h |  2 ++
 include/linux/security.h      |  7 +++++++
 security/security.c           | 17 +++++++++++++++++
 security/selinux/hooks.c      | 26 ++++++++++++++++++++++++++
 security/smack/smack_lsm.c    |  1 +
 security/tomoyo/tomoyo.c      |  1 +
 8 files changed, 59 insertions(+), 2 deletions(-)

diff --git a/fs/ioctl.c b/fs/ioctl.c
index f5fd99d6b0d4..76cf22ac97d7 100644
--- a/fs/ioctl.c
+++ b/fs/ioctl.c
@@ -920,8 +920,7 @@ COMPAT_SYSCALL_DEFINE3(ioctl, unsigned int, fd, unsigned int, cmd,
 	if (!f.file)
 		return -EBADF;
 
-	/* RED-PEN how should LSM module know it's handling 32bit? */
-	error = security_file_ioctl(f.file, cmd, arg);
+	error = security_file_ioctl_compat(f.file, cmd, arg);
 	if (error)
 		goto out;
 
diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 83ef66644c21..170687b5985b 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -751,7 +751,11 @@ static int ovl_security_fileattr(const struct path *realpath, struct fileattr *f
 	else
 		cmd = fa->fsx_valid ? FS_IOC_FSGETXATTR : FS_IOC_GETFLAGS;
 
+#ifdef CONFIG_COMPAT
+	err = security_file_ioctl_compat(file, cmd, 0);
+# else
 	err = security_file_ioctl(file, cmd, 0);
+#endif
 	fput(file);
 
 	return err;
diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index ac962c4cb44b..626aa8cf930d 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -171,6 +171,8 @@ LSM_HOOK(int, 0, file_alloc_security, struct file *file)
 LSM_HOOK(void, LSM_RET_VOID, file_free_security, struct file *file)
 LSM_HOOK(int, 0, file_ioctl, struct file *file, unsigned int cmd,
 	 unsigned long arg)
+LSM_HOOK(int, 0, file_ioctl_compat, struct file *file, unsigned int cmd,
+	 unsigned long arg)
 LSM_HOOK(int, 0, mmap_addr, unsigned long addr)
 LSM_HOOK(int, 0, mmap_file, struct file *file, unsigned long reqprot,
 	 unsigned long prot, unsigned long flags)
diff --git a/include/linux/security.h b/include/linux/security.h
index 5f16eecde00b..22a82b7c59f1 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -389,6 +389,7 @@ int security_file_permission(struct file *file, int mask);
 int security_file_alloc(struct file *file);
 void security_file_free(struct file *file);
 int security_file_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
+int security_file_ioctl_compat(struct file *file, unsigned int cmd, unsigned long arg);
 int security_mmap_file(struct file *file, unsigned long prot,
 			unsigned long flags);
 int security_mmap_addr(unsigned long addr);
@@ -987,6 +988,12 @@ static inline int security_file_ioctl(struct file *file, unsigned int cmd,
 	return 0;
 }
 
+static inline int security_file_ioctl_compat(struct file *file, unsigned int cmd,
+				      unsigned long arg)
+{
+	return 0;
+}
+
 static inline int security_mmap_file(struct file *file, unsigned long prot,
 				     unsigned long flags)
 {
diff --git a/security/security.c b/security/security.c
index 23b129d482a7..5c16ffc99b1e 100644
--- a/security/security.c
+++ b/security/security.c
@@ -2648,6 +2648,23 @@ int security_file_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 }
 EXPORT_SYMBOL_GPL(security_file_ioctl);
 
+/**
+ * security_file_ioctl_compat() - Check if an ioctl is allowed in 32-bit compat mode
+ * @file: associated file
+ * @cmd: ioctl cmd
+ * @arg: ioctl arguments
+ *
+ * Compat version of security_file_ioctl() that correctly handles 32-bit processes
+ * running on 64-bit kernels.
+ *
+ * Return: Returns 0 if permission is granted.
+ */
+int security_file_ioctl_compat(struct file *file, unsigned int cmd, unsigned long arg)
+{
+	return call_int_hook(file_ioctl_compat, 0, file, cmd, arg);
+}
+EXPORT_SYMBOL_GPL(security_file_ioctl_compat);
+
 static inline unsigned long mmap_prot(struct file *file, unsigned long prot)
 {
 	/*
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 2aa0e219d721..de96d156e6ea 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3731,6 +3731,31 @@ static int selinux_file_ioctl(struct file *file, unsigned int cmd,
 	return error;
 }
 
+static int selinux_file_ioctl_compat(struct file *file, unsigned int cmd,
+			      unsigned long arg)
+{
+	// If we are in a 64-bit kernel running 32-bit userspace, we need to make
+	// sure we don't compare 32-bit flags to 64-bit flags.
+	switch (cmd) {
+	case FS_IOC32_GETFLAGS:
+		cmd = FS_IOC_GETFLAGS;
+		break;
+	case FS_IOC32_SETFLAGS:
+		cmd = FS_IOC_GETFLAGS;
+		break;
+	case FS_IOC32_GETVERSION:
+		cmd = FS_IOC_GETVERSION;
+		break;
+	case FS_IOC32_SETVERSION:
+		cmd = FS_IOC_SETVERSION;
+		break;
+	default:
+		break;
+	}
+
+	return selinux_file_ioctl(file, cmd, arg);
+}
+
 static int default_noexec __ro_after_init;
 
 static int file_map_prot_check(struct file *file, unsigned long prot, int shared)
@@ -7036,6 +7061,7 @@ static struct security_hook_list selinux_hooks[] __ro_after_init = {
 	LSM_HOOK_INIT(file_permission, selinux_file_permission),
 	LSM_HOOK_INIT(file_alloc_security, selinux_file_alloc_security),
 	LSM_HOOK_INIT(file_ioctl, selinux_file_ioctl),
+	LSM_HOOK_INIT(file_ioctl_compat, selinux_file_ioctl_compat),
 	LSM_HOOK_INIT(mmap_file, selinux_mmap_file),
 	LSM_HOOK_INIT(mmap_addr, selinux_mmap_addr),
 	LSM_HOOK_INIT(file_mprotect, selinux_file_mprotect),
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 65130a791f57..1f1ea8529421 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -4973,6 +4973,7 @@ static struct security_hook_list smack_hooks[] __ro_after_init = {
 
 	LSM_HOOK_INIT(file_alloc_security, smack_file_alloc_security),
 	LSM_HOOK_INIT(file_ioctl, smack_file_ioctl),
+	LSM_HOOK_INIT(file_ioctl_compat, smack_file_ioctl),
 	LSM_HOOK_INIT(file_lock, smack_file_lock),
 	LSM_HOOK_INIT(file_fcntl, smack_file_fcntl),
 	LSM_HOOK_INIT(mmap_file, smack_mmap_file),
diff --git a/security/tomoyo/tomoyo.c b/security/tomoyo/tomoyo.c
index 25006fddc964..298d182759c2 100644
--- a/security/tomoyo/tomoyo.c
+++ b/security/tomoyo/tomoyo.c
@@ -568,6 +568,7 @@ static struct security_hook_list tomoyo_hooks[] __ro_after_init = {
 	LSM_HOOK_INIT(path_rename, tomoyo_path_rename),
 	LSM_HOOK_INIT(inode_getattr, tomoyo_inode_getattr),
 	LSM_HOOK_INIT(file_ioctl, tomoyo_file_ioctl),
+	LSM_HOOK_INIT(file_ioctl_compat, tomoyo_file_ioctl),
 	LSM_HOOK_INIT(path_chmod, tomoyo_path_chmod),
 	LSM_HOOK_INIT(path_chown, tomoyo_path_chown),
 	LSM_HOOK_INIT(path_chroot, tomoyo_path_chroot),

base-commit: 196e95aa8305aecafc4e1857b7d3eff200d953b6
-- 
2.43.0.472.g3155946c3a-goog