posix_acl: Clear SGID bit when setting file permissions

commit 07393101 upstream.

When file permissions are modified via chmod(2) and the user is not in
the owning group or capable of CAP_FSETID, the setgid bit is cleared in
inode_change_ok().  Setting a POSIX ACL via setxattr(2) sets the file
permissions as well as the new ACL, but doesn't clear the setgid bit in
a similar way; this allows to bypass the check in chmod(2).  Fix that.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

fs/9p/acl.c

@@ -320,32 +320,26 @@ static int v9fs_xattr_set_acl(struct dentry *dentry, const char *name,
 	case ACL_TYPE_ACCESS:
 		name = POSIX_ACL_XATTR_ACCESS;
 		if (acl) {
-			umode_t mode = inode->i_mode;
-			retval = posix_acl_equiv_mode(acl, &mode);
-			if (retval < 0)
+			struct iattr iattr;
+
+			retval = posix_acl_update_mode(inode, &iattr.ia_mode, &acl);
+			if (retval)
 				goto err_out;
-			else {
-				struct iattr iattr;
-				if (retval == 0) {
-					/*
-					 * ACL can be represented
-					 * by the mode bits. So don't
-					 * update ACL.
-					 */
-					acl = NULL;
-					value = NULL;
-					size = 0;
-				}
-				/* Updte the mode bits */
-				iattr.ia_mode = ((mode & S_IALLUGO) |
-						 (inode->i_mode & ~S_IALLUGO));
-				iattr.ia_valid = ATTR_MODE;
-				/* FIXME should we update ctime ?
-				 * What is the following setxattr update the
-				 * mode ?
+			if (!acl) {
+				/*
+				 * ACL can be represented
+				 * by the mode bits. So don't
+				 * update ACL.
 				 */
-				v9fs_vfs_setattr_dotl(dentry, &iattr);
+				value = NULL;
+				size = 0;
 			}
+			iattr.ia_valid = ATTR_MODE;
+			/* FIXME should we update ctime ?
+			 * What is the following setxattr update the
+			 * mode ?
+			 */
+			v9fs_vfs_setattr_dotl(dentry, &iattr);
 		}
 		break;
 	case ACL_TYPE_DEFAULT:

fs/btrfs/acl.c

@@ -118,11 +118,9 @@ static int btrfs_set_acl(struct btrfs_trans_handle *trans,
 	case ACL_TYPE_ACCESS:
 		name = POSIX_ACL_XATTR_ACCESS;
 		if (acl) {
-			ret = posix_acl_equiv_mode(acl, &inode->i_mode);
-			if (ret < 0)
+			ret = posix_acl_update_mode(inode, &inode->i_mode, &acl);
+			if (ret)
 				return ret;
-			if (ret == 0)
-				acl = NULL;
 		}
 		ret = 0;
 		break;

fs/ext2/acl.c

@@ -206,15 +206,11 @@ ext2_set_acl(struct inode *inode, int type, struct posix_acl *acl)
 		case ACL_TYPE_ACCESS:
 			name_index = EXT2_XATTR_INDEX_POSIX_ACL_ACCESS;
 			if (acl) {
-				error = posix_acl_equiv_mode(acl, &inode->i_mode);
-				if (error < 0)
+				error = posix_acl_update_mode(inode, &inode->i_mode, &acl);
+				if (error)
 					return error;
-				else {
-					inode->i_ctime = CURRENT_TIME_SEC;
-					mark_inode_dirty(inode);
-					if (error == 0)
-						acl = NULL;
-				}
+				inode->i_ctime = CURRENT_TIME_SEC;
+				mark_inode_dirty(inode);
 			}
 			break;
 

fs/ext3/acl.c

@@ -205,15 +205,11 @@ ext3_set_acl(handle_t *handle, struct inode *inode, int type,
 		case ACL_TYPE_ACCESS:
 			name_index = EXT3_XATTR_INDEX_POSIX_ACL_ACCESS;
 			if (acl) {
-				error = posix_acl_equiv_mode(acl, &inode->i_mode);
+				error = posix_acl_update_mode(inode, &inode->i_mode, &acl);
 				if (error < 0)
 					return error;
-				else {
-					inode->i_ctime = CURRENT_TIME_SEC;
-					ext3_mark_inode_dirty(handle, inode);
-					if (error == 0)
-						acl = NULL;
-				}
+				inode->i_ctime = CURRENT_TIME_SEC;
+				ext3_mark_inode_dirty(handle, inode);
 			}
 			break;
 

fs/ext4/acl.c

@@ -211,15 +211,11 @@ ext4_set_acl(handle_t *handle, struct inode *inode, int type,
 	case ACL_TYPE_ACCESS:
 		name_index = EXT4_XATTR_INDEX_POSIX_ACL_ACCESS;
 		if (acl) {
-			error = posix_acl_equiv_mode(acl, &inode->i_mode);
-			if (error < 0)
+			error = posix_acl_update_mode(inode, &inode->i_mode, &acl);
+			if (error)
 				return error;
-			else {
-				inode->i_ctime = ext4_current_time(inode);
-				ext4_mark_inode_dirty(handle, inode);
-				if (error == 0)
-					acl = NULL;
-			}
+			inode->i_ctime = ext4_current_time(inode);
+			ext4_mark_inode_dirty(handle, inode);
 		}
 		break;
 

fs/f2fs/acl.c

@@ -223,12 +223,10 @@ static int f2fs_set_acl(struct inode *inode, int type, struct posix_acl *acl)
 	case ACL_TYPE_ACCESS:
 		name_index = F2FS_XATTR_INDEX_POSIX_ACL_ACCESS;
 		if (acl) {
-			error = posix_acl_equiv_mode(acl, &inode->i_mode);
-			if (error < 0)
+			error = posix_acl_update_mode(inode, &inode->i_mode, &acl);
+			if (error)
 				return error;
 			set_acl_inode(fi, inode->i_mode);
-			if (error == 0)
-				acl = NULL;
 		}
 		break;
 

fs/gfs2/acl.c

@@ -268,15 +268,13 @@ static int gfs2_xattr_system_set(struct dentry *dentry, const char *name,
 
 	if (type == ACL_TYPE_ACCESS) {
 		umode_t mode = inode->i_mode;
-		error = posix_acl_equiv_mode(acl, &mode);
+		struct posix_acl *old_acl = acl;
 
-		if (error <= 0) {
-			posix_acl_release(acl);
-			acl = NULL;
-
-			if (error < 0)
-				return error;
-		}
+		error = posix_acl_update_mode(inode, &mode, &acl);
+		if (error < 0)
+			goto out_release;
+		if (!acl)
+			posix_acl_release(old_acl);
 
 		error = gfs2_set_mode(inode, mode);
 		if (error)

fs/hfsplus/posix_acl.c

@@ -72,8 +72,8 @@ static int hfsplus_set_posix_acl(struct inode *inode,
 	case ACL_TYPE_ACCESS:
 		xattr_name = POSIX_ACL_XATTR_ACCESS;
 		if (acl) {
-			err = posix_acl_equiv_mode(acl, &inode->i_mode);
-			if (err < 0)
+			err = posix_acl_update_mode(inode, &inode->i_mode, &acl);
+			if (err)
 				return err;
 		}
 		err = 0;

fs/hfsplus/xattr.c

@@ -69,8 +69,9 @@ static int can_set_system_xattr(struct inode *inode, const char *name,
 		if (IS_ERR(acl))
 			return PTR_ERR(acl);
 		if (acl) {
-			err = posix_acl_equiv_mode(acl, &inode->i_mode);
-			posix_acl_release(acl);
+			struct posix_acl *old_acl = acl;
+			err = posix_acl_update_mode(inode, &inode->i_mode, &acl);
+			posix_acl_release(old_acl);
 			if (err < 0)
 				return err;
 			mark_inode_dirty(inode);

fs/jffs2/acl.c

@@ -243,9 +243,10 @@ static int jffs2_set_acl(struct inode *inode, int type, struct posix_acl *acl)
 	case ACL_TYPE_ACCESS:
 		xprefix = JFFS2_XPREFIX_ACL_ACCESS;
 		if (acl) {
-			umode_t mode = inode->i_mode;
-			rc = posix_acl_equiv_mode(acl, &mode);
-			if (rc < 0)
+			umode_t mode;
+
+			rc = posix_acl_update_mode(inode, &mode, &acl);
+			if (rc)
 				return rc;
 			if (inode->i_mode != mode) {
 				struct iattr attr;
@@ -257,8 +258,6 @@ static int jffs2_set_acl(struct inode *inode, int type, struct posix_acl *acl)
 				if (rc < 0)
 					return rc;
 			}
-			if (rc == 0)
-				acl = NULL;
 		}
 		break;
 	case ACL_TYPE_DEFAULT:

fs/jfs/xattr.c

@@ -693,8 +693,9 @@ static int can_set_system_xattr(struct inode *inode, const char *name,
 			return rc;
 		}
 		if (acl) {
-			rc = posix_acl_equiv_mode(acl, &inode->i_mode);
-			posix_acl_release(acl);
+			struct posix_acl *old_acl = acl;
+			rc = posix_acl_update_mode(inode, &inode->i_mode, &acl);
+			posix_acl_release(old_acl);
 			if (rc < 0) {
 				printk(KERN_ERR
 				       "posix_acl_equiv_mode returned %d\n",

fs/ocfs2/acl.c

@@ -270,20 +270,14 @@ static int ocfs2_set_acl(handle_t *handle,
 	case ACL_TYPE_ACCESS:
 		name_index = OCFS2_XATTR_INDEX_POSIX_ACL_ACCESS;
 		if (acl) {
-			umode_t mode = inode->i_mode;
-			ret = posix_acl_equiv_mode(acl, &mode);
-			if (ret < 0)
+			umode_t mode;
+			ret = posix_acl_update_mode(inode, &mode, &acl);
+			if (ret)
+				return ret;
+			ret = ocfs2_acl_set_mode(inode, di_bh,
+						 handle, mode);
+			if (ret)
 				return ret;
-			else {
-				if (ret == 0)
-					acl = NULL;
-
-				ret = ocfs2_acl_set_mode(inode, di_bh,
-							 handle, mode);
-				if (ret)
-					return ret;
-
-			}
 		}
 		break;
 	case ACL_TYPE_DEFAULT:

fs/posix_acl.c

@@ -407,6 +407,37 @@ posix_acl_create(struct posix_acl **acl, gfp_t gfp, umode_t *mode_p)
 }
 EXPORT_SYMBOL(posix_acl_create);
 
+/**
+ * posix_acl_update_mode  -  update mode in set_acl
+ *
+ * Update the file mode when setting an ACL: compute the new file permission
+ * bits based on the ACL.  In addition, if the ACL is equivalent to the new
+ * file mode, set *acl to NULL to indicate that no ACL should be set.
+ *
+ * As with chmod, clear the setgit bit if the caller is not in the owning group
+ * or capable of CAP_FSETID (see inode_change_ok).
+ *
+ * Called from set_acl inode operations.
+ */
+int posix_acl_update_mode(struct inode *inode, umode_t *mode_p,
+                          struct posix_acl **acl)
+{
+        umode_t mode = inode->i_mode;
+        int error;
+
+        error = posix_acl_equiv_mode(*acl, &mode);
+        if (error < 0)
+                return error;
+        if (error == 0)
+                *acl = NULL;
+        if (!in_group_p(inode->i_gid) &&
+            !capable_wrt_inode_uidgid(inode, CAP_FSETID))
+                mode &= ~S_ISGID;
+        *mode_p = mode;
+        return 0;
+}
+EXPORT_SYMBOL(posix_acl_update_mode);
+
 int
 posix_acl_chmod(struct posix_acl **acl, gfp_t gfp, umode_t mode)
 {

fs/reiserfs/xattr_acl.c

@@ -288,13 +288,9 @@ reiserfs_set_acl(struct reiserfs_transaction_handle *th, struct inode *inode,
 	case ACL_TYPE_ACCESS:
 		name = POSIX_ACL_XATTR_ACCESS;
 		if (acl) {
-			error = posix_acl_equiv_mode(acl, &inode->i_mode);
-			if (error < 0)
+			error = posix_acl_update_mode(inode, &inode->i_mode, &acl);
+			if (error)
 				return error;
-			else {
-				if (error == 0)
-					acl = NULL;
-			}
 		}
 		break;
 	case ACL_TYPE_DEFAULT:

fs/xfs/xfs_acl.c

@@ -402,16 +402,15 @@ xfs_xattr_acl_set(struct dentry *dentry, const char *name,
 		goto out_release;
 
 	if (type == ACL_TYPE_ACCESS) {
-		umode_t mode = inode->i_mode;
-		error = posix_acl_equiv_mode(acl, &mode);
+		umode_t mode;
+		struct posix_acl *old_acl = acl;
 
-		if (error <= 0) {
-			posix_acl_release(acl);
-			acl = NULL;
+		error = posix_acl_update_mode(inode, &mode, &acl);
 
-			if (error < 0)
-				return error;
-		}
+		if (error)
+			goto out_release;
+		if (!acl)
+			posix_acl_release(old_acl);
 
 		error = xfs_set_mode(inode, mode);
 		if (error)

include/linux/posix_acl.h

@@ -89,6 +89,7 @@ extern int posix_acl_permission(struct inode *, const struct posix_acl *, int);
 extern struct posix_acl *posix_acl_from_mode(umode_t, gfp_t);
 extern int posix_acl_equiv_mode(const struct posix_acl *, umode_t *);
 extern int posix_acl_create(struct posix_acl **, gfp_t, umode_t *);
+extern int posix_acl_update_mode(struct inode *, umode_t *, struct posix_acl **);
 extern int posix_acl_chmod(struct posix_acl **, gfp_t, umode_t);
 
 extern struct posix_acl *get_posix_acl(struct inode *, int);