selinux: enable per-file labeling for debugfs files.

upstream commit 6f29997f4a3117169eeabd41dbea4c1bd94a739c

Add support for per-file labeling of debugfs files so that
we can distinguish them in policy.  This is particularly
important in Android where certain debugfs files have to be writable
by apps and therefore the debugfs directory tree can be read and
searched by all.

Since debugfs is entirely kernel-generated, the directory tree is
immutable by userspace, and the inodes are pinned in memory, we can
simply use the same approach as with proc and label the inodes from
policy based on pathname from the root of the debugfs filesystem.
Generalize the existing labeling support used for proc and reuse it
for debugfs too.

[sds:  Back-ported to 3.4.  superblock_security_struct flags field
is only unsigned char in 3.4 so we have to redefine SE_SBGENFS.
However, this definition is kernel-private, not exposed to userspace
or stored anywhere persistent.  Also depends on
I7742b4b7e53b45e4dd13d99c39553a927aa4a7e9.]

Change-Id: I6460fbed6bb6bd36eb8554ac8c4fdd574edf3b07
Signed-off-by: Stephen Smalley <[email protected]>

security/selinux/hooks.c

@@ -692,7 +692,10 @@ static int selinux_set_mnt_opts(struct super_block *sb,
 	}
 
 	if (strcmp(sb->s_type->name, "proc") == 0)
-		sbsec->flags |= SE_SBPROC;
+		sbsec->flags |= SE_SBPROC | SE_SBGENFS;
+
+	if (strcmp(sb->s_type->name, "debugfs") == 0)
+		sbsec->flags |= SE_SBGENFS;
 
 	/* Determine the labeling behavior to use for this filesystem type. */
 	rc = security_fs_use((sbsec->flags & SE_SBPROC) ? "proc" : sb->s_type->name, &sbsec->behavior, &sbsec->sid);
@@ -1146,12 +1149,13 @@ static inline u16 socket_type_to_security_class(int family, int type, int protoc
 	return SECCLASS_SOCKET;
 }
 
-#ifdef CONFIG_PROC_FS
-static int selinux_proc_get_sid(struct dentry *dentry,
-				u16 tclass,
-				u32 *sid)
+static int selinux_genfs_get_sid(struct dentry *dentry,
+				 u16 tclass,
+				 u16 flags,
+				 u32 *sid)
 {
 	int rc;
+	struct super_block *sb = dentry->d_inode->i_sb;
 	char *buffer, *path;
 
 	buffer = (char *)__get_free_page(GFP_KERNEL);
@@ -1162,26 +1166,20 @@ static int selinux_proc_get_sid(struct dentry *dentry,
 	if (IS_ERR(path))
 		rc = PTR_ERR(path);
 	else {
-		/* each process gets a /proc/PID/ entry. Strip off the
-		 * PID part to get a valid selinux labeling.
-		 * e.g. /proc/1/net/rpc/nfs -> /net/rpc/nfs */
-		while (path[1] >= '0' && path[1] <= '9') {
-			path[1] = '/';
-			path++;
+		if (flags & SE_SBPROC) {
+			/* each process gets a /proc/PID/ entry. Strip off the
+			 * PID part to get a valid selinux labeling.
+			 * e.g. /proc/1/net/rpc/nfs -> /net/rpc/nfs */
+			while (path[1] >= '0' && path[1] <= '9') {
+				path[1] = '/';
+				path++;
+			}
 		}
-		rc = security_genfs_sid("proc", path, tclass, sid);
+		rc = security_genfs_sid(sb->s_type->name, path, tclass, sid);
 	}
 	free_page((unsigned long)buffer);
 	return rc;
 }
-#else
-static int selinux_proc_get_sid(struct dentry *dentry,
-				u16 tclass,
-				u32 *sid)
-{
-	return -EINVAL;
-}
-#endif
 
 /* The inode's security attributes must be initialized before first use. */
 static int inode_doinit_with_dentry(struct inode *inode, struct dentry *opt_dentry)
@@ -1336,7 +1334,7 @@ static int inode_doinit_with_dentry(struct inode *inode, struct dentry *opt_dent
 		/* Default to the fs superblock SID. */
 		isec->sid = sbsec->sid;
 
-		if ((sbsec->flags & SE_SBPROC) && !S_ISLNK(inode->i_mode)) {
+		if ((sbsec->flags & SE_SBGENFS) && !S_ISLNK(inode->i_mode)) {
 			/* We must have a dentry to determine the label on
 			 * procfs inodes */
 			if (opt_dentry)
@@ -1359,7 +1357,8 @@ static int inode_doinit_with_dentry(struct inode *inode, struct dentry *opt_dent
 			if (!dentry)
 				goto out_unlock;
 			isec->sclass = inode_mode_to_security_class(inode->i_mode);
-			rc = selinux_proc_get_sid(dentry, isec->sclass, &sid);
+			rc = selinux_genfs_get_sid(dentry, isec->sclass,
+						   sbsec->flags, &sid);
 			dput(dentry);
 			if (rc)
 				goto out_unlock;

security/selinux/include/security.h

@@ -51,6 +51,7 @@
 #define SE_SBINITIALIZED	0x10
 #define SE_SBPROC		0x20
 #define SE_SBLABELSUPP	0x40
+#define SE_SBGENFS	0x80
 
 #define CONTEXT_STR	"context="
 #define FSCONTEXT_STR	"fscontext="