8:19 p.m.
Not enabled by default, because of the potential security concern that
a client can use this to sniff what file names exist in the image; but
for an opt-in setting in the server, this lets a single nbdkit process
serve multiple files from an ext2 image (one at a time, unless we find
a way to allow a filter to open the plugin once without a current
connection, then share that opened plugin across multiple client
connections).
In testing this manually, I learned that qemu 4.0 fails to preserve
leading / in nbd://host:port//path/to/file (no matter how many slashes
you add), so the code here adds a leading slash to be nice to clients
like broken qemu.
Signed-off-by: Eric Blake <eblake(a)redhat.com>
---
filters/ext2/ext2.c | 35 ++++++++++++++++++++---------
filters/ext2/nbdkit-ext2-filter.pod | 10 +++++++++
2 files changed, 35 insertions(+), 10 deletions(-)
diff --git a/filters/ext2/ext2.c b/filters/ext2/ext2.c
index d53743cd..92c8601a 100644
--- a/filters/ext2/ext2.c
+++ b/filters/ext2/ext2.c
@@ -50,7 +50,7 @@
#include "cleanup.h"
#include "io.h"
-/* Filename parameter. */
+/* Filename parameter, or NULL to honor export name. */
static char *file;
static void
@@ -94,7 +94,11 @@ ext2_config_complete (nbdkit_next_config_complete *next, void *nxdata)
return -1;
}
- if (file[0] != '/') {
+ if (strcmp (file, "exportname") == 0) {
+ free (file);
+ file = NULL;
+ }
+ else if (file[0] != '/') {
nbdkit_error ("the file parameter must refer to an absolute path");
return -1;
}
@@ -103,7 +107,8 @@ ext2_config_complete (nbdkit_next_config_complete *next, void
*nxdata)
}
#define ext2_config_help \
- "ext2file=<FILENAME> (required) File to serve inside the disk image."
+ "ext2file=<FILENAME> (required) Absolute name of file to serve inside
the\n" \
+ " disk image, or 'exportname' for client
choice."
/* The per-connection handle. */
struct handle {
@@ -143,6 +148,8 @@ ext2_prepare (struct nbdkit_next_ops *next_ops, void *nxdata, void
*handle,
struct ext2_inode inode;
int64_t r;
CLEANUP_FREE char *name = NULL;
+ const char *fname = file ?: nbdkit_export_name ();
+ CLEANUP_FREE char *absname = NULL;
fs_flags = 0;
#ifdef EXT2_FLAG_64BITS
@@ -168,34 +175,42 @@ ext2_prepare (struct nbdkit_next_ops *next_ops, void *nxdata, void
*handle,
return -1;
}
+ if (fname[0] != '/') {
+ if (asprintf (&absname, "/%s", fname) < 0) {
+ nbdkit_error ("asprintf: %m");
+ return -1;
+ }
+ fname = absname;
+ }
+
err = ext2fs_open (name, fs_flags, 0, 0, nbdkit_io_manager, &h->fs);
if (err != 0) {
nbdkit_error ("open: %s", error_message (err));
goto err0;
}
- if (strcmp (file, "/") == 0)
+ if (strcmp (fname, "/") == 0)
/* probably gonna fail, but we'll catch it later */
h->ino = EXT2_ROOT_INO;
else {
err = ext2fs_namei (h->fs, EXT2_ROOT_INO, EXT2_ROOT_INO,
- &file[1], &h->ino);
+ &fname[1], &h->ino);
if (err != 0) {
- nbdkit_error ("%s: namei: %s", file, error_message (err));
+ nbdkit_error ("%s: namei: %s", fname, error_message (err));
goto err1;
}
}
- /* Check the file is a regular file.
+ /* Check that fname is a regular file.
* XXX This won't follow symlinks, we'd have to do that manually.
*/
err = ext2fs_read_inode (h->fs, h->ino, &inode);
if (err != 0) {
- nbdkit_error ("%s: inode: %s", file, error_message (err));
+ nbdkit_error ("%s: inode: %s", fname, error_message (err));
goto err1;
}
if (!LINUX_S_ISREG (inode.i_mode)) {
- nbdkit_error ("%s: must be a regular file in the disk image", file);
+ nbdkit_error ("%s: must be a regular file in the disk image", fname);
goto err1;
}
@@ -204,7 +219,7 @@ ext2_prepare (struct nbdkit_next_ops *next_ops, void *nxdata, void
*handle,
file_flags |= EXT2_FILE_WRITE;
err = ext2fs_file_open2 (h->fs, h->ino, NULL, file_flags, &h->file);
if (err != 0) {
- nbdkit_error ("%s: open: %s", file, error_message (err));
+ nbdkit_error ("%s: open: %s", fname, error_message (err));
goto err1;
}
diff --git a/filters/ext2/nbdkit-ext2-filter.pod b/filters/ext2/nbdkit-ext2-filter.pod
index c0927637..d621ee45 100644
--- a/filters/ext2/nbdkit-ext2-filter.pod
+++ b/filters/ext2/nbdkit-ext2-filter.pod
@@ -7,6 +7,9 @@ ext4 filesystems
nbdkit --filter=ext2 file fs.img ext2file=/disks/disk.raw
+ nbdkit --filter=ext2 --filter=partition file fs.img \
+ partition=1 ext2file=exportname
+
=head1 DESCRIPTION
C<nbdkit-ext2-filter> is an nbdkit filter which can read and
@@ -55,6 +58,13 @@ e2fsprogs.
The full path of the file within the filesystem that will be exposed
over NBD. The path must be absolute (starts with C</>).
+=item B<ext2file=exportname>
+
+The plugin will expose the path within the filesystem chosen by the
+exportname passed by the client. Note that this mode allows the
+client to deduce which files exist within the disk image, which may be
+a security risk in some situations.
+
=back
=head1 FILES
--
2.24.1