Infinite loop in collectstatic with broken symlinks

[Matthew Somerville]

If the static directory contains a broken symlink in place of a file that collectstatic wishes to copy*, then the code gets stuck in an infinite loop, because the os.open fails (O_CREAT | O_EXCL will fail if a symlink exists, even if it's to a non-existent file), but then get_available_name returns the same name (as it calls self.exists, which returns False for a broken symlink).

I guess two possibilities are:

1. don't care about broken symlinks. Change the flags setting in django/core/files/storage.py to not include O_EXCL if os.path.islink(full_path) and not os.path.exists(full_path).
2. do care, change os.path.exists in the exists function to use os.path.lexists instead.

I'm not sure which would be preferable to prevent this infinite loop.

*I came across this issue because collectstatic had been run both inside and outside a Vagrant box, so symlinks created inside the box did not exist when collectstatic was then run outside.

[KwonHan Bae]

I think its fixed in master branch.
should we backport to 11.x ?

[Tim Graham]

Which commit fixed it? Most likely a fix wouldn't qualify for a backport based on our ​supported versions policy.

[Jacob Walls]

Decided to reproduce this on main. Still can.

I'm preparing a tiny patch using the second possibility from the ticket description: using os.path.lexists() in FileSystemStorage.exists().

[Jacob Walls]

I reproduced this outside of contrib.staticfiles by just providing a broken symlink to FileSystemStorage.save() and never exiting a while loop. I'm hoping this is a welcome root cause to look at.

​PR

[Mariusz Felisiak <felisiak.mariusz@…>]

In ec2727ef:

Fixed #28154 -- Prevented infinite loop in FileSystemStorage.save() when a broken symlink with the same name exists.