readlink: Behaviour differs from GNU Coreutils when path exists but cannot be read

[aidanharris]

Running as a non-root user that does not have permission to read /proc/1/exe (since the init process is started as root):

Expected:

$ readlink -f /proc/1/exe /etc/hosts
/etc/hosts

Actual:

$ readlink -f /proc/1/exe /etc/hosts
/proc/1/exe
/etc/hosts

We do see the error raised correctly when Uutils doesn't canonicalize the path:

$ readlink -v /proc/1/exe /etc/hosts
readlink: /proc/1/exe: Permission denied

But it's returning early instead of processing the rest of the files:

GNU Coreutils

$ readlink -v -e /proc/1/exe /etc/hosts
readlink: /proc/1/exe: Permission denied
/etc/hosts

Running

[samueltardieu]

I wonder whether GNU readlink -f /proc/1/exe /etc/hosts displaying only /etc/hosts is right. The description for -f on https://www.gnu.org/software/coreutils/manual/html_node/readlink-invocation.html#readlink-invocation is:

Activate canonicalize mode. If any component of the file name except the last one is missing or unavailable, readlink produces no output and exits with a nonzero exit code. A trailing slash is ignored.

Aren't all the components of the file name /proc/1/exe except the last one present and available?