Initialize selinuxfs as a pseudo filesystem. This raises SB_I_PSEUDO and SB_I_NOEXEC. selinuxfs never holds executables. SB_I_NOEXEC also refuses PROT_EXEC mappings but the status and policy files are only ever mapped for reading.
But selinuxfs needs device nodes. The kernel replaces file descriptors with /sys/fs/selinux/null on exec via dentry_open() which doesn't care about SB_I_NODEV. Android init however opens /sys/fs/selinux/null by path as /dev/null doesn't exist yet at that point. So clear SB_I_NODEV again in sel_fill_super(). Signed-off-by: Christian Brauner (Amutable) <[email protected]> --- security/selinux/selinuxfs.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c index 310e19efff1d..d7ae853b6d68 100644 --- a/security/selinux/selinuxfs.c +++ b/security/selinux/selinuxfs.c @@ -18,6 +18,7 @@ #include <linux/vmalloc.h> #include <linux/fs.h> #include <linux/fs_context.h> +#include <linux/pseudo_fs.h> #include <linux/hex.h> #include <linux/mount.h> #include <linux/mutex.h> @@ -1852,6 +1853,9 @@ static int sel_fill_super(struct super_block *sb, struct fs_context *fc) /* last one */ {"", NULL, 0} }; + /* Android init opens the null device below by path. */ + sb->s_iflags &= ~SB_I_NODEV; + ret = selinux_fs_info_create(sb); if (ret) goto err; @@ -1955,6 +1959,7 @@ static const struct fs_context_operations sel_context_ops = { static int sel_init_fs_context(struct fs_context *fc) { + fc_init_pseudo(fc); fc->ops = &sel_context_ops; return 0; } -- 2.53.0
