From: Miklos Szeredi <mszeredi@xxxxxxx> Add a new filesystem flag, that results in the VFS not checking if the current process has enough privileges to do an mknod(). This is needed on filesystems, where an unprivileged user may be able to create a device node, without causing security problems. One such example is "mountlo" a loopback mount utility implemented with fuse and UML, which runs as an unprivileged userspace process. In this case the user does in fact have the right to create device nodes within the filesystem image, as long as the user has write access to the image. Since the filesystem is mounted with "nodev", adding device nodes is not a security concern. This feature is basically "fuse-only", so it does not make sense to change the semantics of ->mknod(). Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxx> --- Index: linux/fs/namei.c =================================================================== --- linux.orig/fs/namei.c 2007-08-09 16:49:07.000000000 +0200 +++ linux/fs/namei.c 2007-08-09 16:49:12.000000000 +0200 @@ -1921,7 +1921,8 @@ int vfs_mknod(struct inode *dir, struct if (error) return error; - if ((S_ISCHR(mode) || S_ISBLK(mode)) && !capable(CAP_MKNOD)) + if (!(dir->i_sb->s_type->fs_flags & FS_MKNOD_CHECKS_PERM) && + (S_ISCHR(mode) || S_ISBLK(mode)) && !capable(CAP_MKNOD)) return -EPERM; if (!dir->i_op || !dir->i_op->mknod) Index: linux/include/linux/fs.h =================================================================== --- linux.orig/include/linux/fs.h 2007-08-09 16:49:07.000000000 +0200 +++ linux/include/linux/fs.h 2007-08-09 16:49:12.000000000 +0200 @@ -97,6 +97,7 @@ extern int dir_notify_enable; #define FS_BINARY_MOUNTDATA 2 #define FS_HAS_SUBTYPE 4 #define FS_SAFE 8 /* Safe to mount by unprivileged users */ +#define FS_MKNOD_CHECKS_PERM 16 /* FS checks if device creation is allowed */ #define FS_REVAL_DOT 16384 /* Check the paths ".", ".." for staleness */ #define FS_RENAME_DOES_D_MOVE 32768 /* FS will handle d_move() * during rename() internally. -- - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
