podman cp: unexpected mkdir on symlink expansion

[edsantiago]

podman cp into a container, when the destination argument is a symlink pointing to a nonexistent path, and includes a trailing slash, will (surprisingly) mkdir that path:

# podman run -d --name cpc alpine sh -c 'sleep 999'
2c216ec654f5062d444d600f4dfabace3b01418b518fecafa5ba3e4074127655

! Create three tmp directories, d1 d2 d3, the first two with 
! a symlink 'x' pointing nowhere
# podman exec cpc sh -c 'mkdir /tmp/d1;ln -s /tmp/nonesuch1 /tmp/d1/x'
# podman exec cpc sh -c 'mkdir /tmp/d2;ln -s /tmp/nonesuch2 /tmp/d2/x'
# podman exec cpc sh -c 'mkdir /tmp/d3'
# podman exec cpc ls -lR /tmp
/tmp:
total 24
drwxr-xr-x    2 root     root          4096 Aug 27 19:35 d1
drwxr-xr-x    2 root     root          4096 Aug 27 19:35 d2
drwxr-xr-x    2 root     root          4096 Aug 27 19:35 d3

/tmp/d1:
total 0
lrwxrwxrwx    1 root     root            14 Aug 27 19:35 x -> /tmp/nonesuch1

/tmp/d2:
total 0
lrwxrwxrwx    1 root     root            14 Aug 27 19:35 x -> /tmp/nonesuch2

/tmp/d3:
total 0

! Create a file and copy it into the container in three different ways
# echo hi >/tmp/myfile
# podman cp /tmp/myfile cpc:/tmp/d1/x
# podman cp /tmp/myfile cpc:/tmp/d2/x/     <<<<---- note trailing slash!
# podman cp /tmp/myfile cpc:/tmp/d3/x
# podman exec cpc ls -lR /tmp
/tmp:
total 36
drwxr-xr-x    2 root     root          4096 Aug 27 19:35 d1
drwxr-xr-x    2 root     root          4096 Aug 27 19:35 d2
drwxr-xr-x    2 root     root          4096 Aug 27 19:36 d3
-rw-r--r--    1 root     root             3 Aug 27 19:36 nonesuch1    <<<<< weird
drwxr-xr-x    2 root     root          4096 Aug 27 19:36 nonesuch2    <<<<< weirder

/tmp/d1:
total 0
lrwxrwxrwx    1 root     root            14 Aug 27 19:35 x -> /tmp/nonesuch1

/tmp/d2:
total 0
lrwxrwxrwx    1 root     root            14 Aug 27 19:35 x -> /tmp/nonesuch2

/tmp/d3:
total 4
-rw-r--r--    1 root     root             3 Aug 27 19:36 x

/tmp/nonesuch2:
total 4
-rw-r--r--    1 root     root             3 Aug 27 19:36 myfile

When copying to /tmp/d1/x, where x points to nonexistent /tmp/nonesuch1, podman created the file /tmp/nonesuch1. This is weird: I would've expected an error (dangling symlink). But this is the same behavior as docker-1.13.1-103.git7f2769b.el7, so maybe we have to live with it.

When copying to /tmp/d2/x/, same as above but with a trailing slash, podman actually mkdir()s the dangling nonexistent directory, then places the file in that directory with the same name as the source file. This, I think, is bizarre and entirely wrong. (docker fails with 'no such directory').

podman master @ f221c61

[mheon]

While this definitely sounds like a bug - can you confirm that Docker doesn't do this? It seems like a sufficiently obscure case that I'm honestly not sure what the right thing to do it...

[edsantiago]

I confirmed it yesterday with docker-1.13.1-103.git7f2769b.el7: fails with 'no such directory'

[mheon]

Alright, that's our intended behavior, then
@QiWang19 PTAL

[TomSweeneyRedHat]

@QiWang19 as a note, the test that @edsantiago recently put in will most likely fail after you correct this and you will need to adjust it to mirror the correct behavior.