extfs: debugfs rdump preserve flags

[qkaiser]

The Origins

I'm not exactly sure if the root of the problem lies in the file we got or in the way debugfs is implemented, but we end up with a directory that looks like this after debugfs stopped shouting at us that it failed changing ownership.

total 0
d????????? ? ? ? ?            ? .
d????????? ? ? ? ?            ? ..
-????????? ? ? ? ?            ? alt.png
-????????? ? ? ? ?            ? clipboard.png
-????????? ? ? ? ?            ? connect.png
-????????? ? ? ? ?            ? ctrlaltdel.png
-????????? ? ? ? ?            ? ctrl.png

Command "Design"

debugfs implements two dumping commands:

• dump or dump_inode: works on files
• rdump: works on directories

The two interfaces differ:

Usage: dump_inode [-p] <file> <output_file>
Usage: rdump <directory>... <native directory>

The -p parameter in dump_inode corresponds to preserve, a mode in which debugfs will do its best to preserve permissions and ownership of the files.

The problem is that rdump does not expose such a flag and implicitly considers the preserve flag to be set to 1. In rdump_inode, the following call is made:

if (dump_file("rdump", ino, fd, 1, fullname) != 0) {

With the definition of being:

static int dump_file(const char *cmdname, ext2_ino_t ino, int fd, int preserve, char *outname)

So we have two problems here:

• we don't want to preserve permissions with unblob, because it leads to all kinds of noise with corrupted file systems or filesystems where all the files are owned by root
• the call to dump_file done by rdump_inode with an implicit preserve flag is really bad design

Fix ?

A naive fix is this one:

diff --git a/debugfs/dump.c b/debugfs/dump.c
index b8a46eac..2ab84e7d 100644
--- a/debugfs/dump.c
+++ b/debugfs/dump.c
@@ -281,7 +281,7 @@ static void rdump_inode(ext2_ino_t ino, struct ext2_inode *inode,
                        com_err("rdump", errno, "while opening %s", fullname);
                        goto errout;
                }
-               if (dump_file("rdump", ino, fd, 1, fullname) != 0) {
+               if (dump_file("rdump", ino, fd, 0, fullname) != 0) {
       com_err("rdump", errno, "while dumping %s", fullname);
                        free(fullname);
       exit(1);
@@ -307,7 +307,7 @@ static void rdump_inode(ext2_ino_t ino, struct ext2_inode *inode,
                if (retval)
                        com_err("rdump", retval, "while dumping %s", fullname);
 
-               fix_perms("rdump", inode, -1, fullname);
+               //fix_perms("rdump", inode, -1, fullname);
        }
        /* else do nothing (don't dump device files, sockets, fifos, etc.) */

But the rdump interface must be modified to accept a preserve flag so that we can explicitly tell it not to preserve with unblob.

[qkaiser]

As indicated by the great @e3krisztian:

This can happen if we have r, but not x permission for a directory: its content can be enumerated (read) as names, but access to details (inode) is restricted.

[qkaiser]

Being taken care of at onekey-sec/e2fsprogs#8