syscall: follow trusted sender ancestor links

[steadytao]

Fixes #1087

Summary

Explicit sender command-line arguments now establish transfer roots and may pass through ancestor symlinks regardless of ownership. This covers absolute and relative directory sources as well as direct file sources used with --relative, while keeping recursive traversal confined beneath the selected source root.

--files-from entries follow only trusted-owned ancestor symlinks because the source base is operator-selected but individual list entries are not. File-leaf symlinks remain refused unless an existing symlink-following option is enabled.

Daemon confinement remains unchanged.

[steadytao]

@peabee Could you test this with your backup application using the original /mnt/home/My_Documents path? Please check that the backup completes and the expected files are copied.

[peabee]

Hi happy to test but unsure what "this" is or how to obtain it......
A binary would be ideal......
But if you want me to download source and compile I don't know how to download source with a pull request included - sorry!

[steadytao]

This is built against TrixiePup64, so it may not run on your Slackware-based Puppy - rsync.tar.gz

Make sure to keep your existing rsync; if this binary reports a library error, send me that error and your exact Puppy version/environment so I can provide a matching build.

[steadytao]

Ah and you can use git clone --single-branch --branch sender-ancestor-links https://github.com/RsyncProject/rsync.git to clone the PR if that is easier.

[seks99x]

Great job! there is still another case not covered. File transfers using the -R (--relative) flag are still broken across the board if a symlink is included in the path (full/relative paths). Directories or recursive transfers works well with full/relative paths.

┌──(root㉿192)-[~/rsync-latest-news]
└─# rsync/rsync -R rsync/lnk/test/a /home/omar/dest/ -> rel/full path case
rsync: [sender] send_files failed to open "/root/rsync-latest-news/rsync/lnk/test/a": Too many levels of symbolic links (40)
rsync error: some files/attrs were not transferred (see previous errors) (code 23) at main.c(1404) [sender=3.5.0-gd0a5ab7f]

Expected Behavior (rsync 3.4.1)
seks@omars-Mac-mini rsync-3.4.1 % ./rsync -R lnk/sub/a dest/ 
seks@omars-Mac-mini rsync-3.4.1 % ls dest/
lnk

[peabee]

This is built against TrixiePup64, so it may not run on your Slackware-based Puppy - rsync.tar.gz

Make sure to keep your existing rsync; if this binary reports a library error, send me that error and your exact Puppy version/environment so I can provide a matching build.

Sorry for the delay in responding....
Many thanks for the binary - appreciated - all dependencies were satisfied.
I can confirm that with this version, the backup to /mnt/home/My_Documents where /mnt/home is a symlink works successfully - no errors.
Looking forward to the new version appearing.
Thanks.

[steadytao]

Much appreciated. The new version should be released on the 21st for as long we catch no more edge/corner cases.

[seks99x]

files-from uses relative by default and still broken. They should be following only trusted symlinks because we are inside the operators-tree.

┌──(root㉿192)-[~/rsync-latest-news/rsync]
└─# ./rsync -av --files-from=/root/rsync-latest-news/rsync/files.txt /root/rsync-latest-news/seks99x/batch/rsync/  /home/omar/dest/
building file list ... done
rsync: [sender] send_files failed to open "/root/rsync-latest-news/seks99x/batch/rsync/lnk/test/a": Too many levels of symbolic links (40)

sent 185 bytes  received 31 bytes  432.00 bytes/sec
total size is 1,057  speedup is 4.89
rsync error: some files/attrs were not transferred (see previous errors) (code 23) at main.c(1404) [sender=3.5.0-gc9f8e21f]
                                                                                                                                                                            
┌──(root㉿192)-[~/rsync-latest-news/rsync]
└─# ls -al lnk                                                                                                                     
lrwxrwxrwx 1 root root 10 Sep 15 18:34 lnk -> /etc/omar/
                                                                                                                                                                            
┌──(root㉿192)-[~/rsync-latest-news/rsync]
└─# cat files.txt            
lnk/test/a. -> contains symlink

Expected Behavior (rsync 3.4.1)
seks@omars-Mac-mini rsync-3.4.1 % ./rsync -av --files-from=files.txt . dest/
building file list ... done
lnk/
lnk/sub/
lnk/sub/a

sent 161 bytes  received 41 bytes  404.00 bytes/sec
total size is 3  speedup is 0.01

seks@omars-Mac-mini rsync-3.4.1 % cat files.txt 
lnk/sub/a -> contains symlink
                                                                                                                                                                            

[steadytao]

Ahhhh true. Thank you.

[seks99x]

If a directory listed in --files-from contains or leads through a trusted symlink, traversing it fails . Trusted symlinks in the path should be followed correctly here.
Files are working right, if I changed the path to lnk/test/a it will work as expected.

┌──(root㉿192)-[~/rsync-latest-news/rsync]
└─# ./rsync -av --files-from=/root/rsync-latest-news/rsync/fi . /home/omar/dest/
building file list ... 
rsync: [sender] opendir "/root/rsync-latest-news/rsync/lnk/test" failed: Too many levels of symbolic links (40)
done
lnk/
lnk/test/

sent 84 bytes  received 22 bytes  212.00 bytes/sec
total size is 0  speedup is 0.00
rsync error: some files/attrs were not transferred (see previous errors) (code 23) at main.c(1404) [sender=3.5.0-ge7a40140]
                                                                                                                                                                            
┌──(root㉿192)-[~/rsync-latest-news/rsync]
└─# cat fi                
lnk/test/
                                                                                                                                                                            
┌──(root㉿192)-[~/rsync-latest-news/rsync]
└─# ll lnk
lrwxrwxrwx 1 root root 10 Sep 15 18:34 lnk -> /etc/omar/
                                                                                                                                                                            
┌──(root㉿192)-[~/rsync-latest-news/rsync]
└─# 

[steadytao]

Oof ye. Okay give me more time on this. Good to get a rough shape and it semi-working but it needs a lot more for proper coverage.

[seks99x]

Take your time, mate! Symlinks are an absolute mess in this codebase😂

[steadytao]

Symlinks are an absolute mess everywhere. I need to start a revolt!!!