Description:

bash is by default installed as /usr/bin/bash, with a symlink in /bin, but /usr/bin/bash is not listed as a valid user shell in /etc/shells by default.

Since /usr/bin is before /bin in the default PATH, if one adds a user with a command like

# useradd [...] -s $(which bash) myuser

this user will be unable to login from system console (or via any PAM path that uses pam_shells.so)

Additional info:

/etc/shells from filesystem 2013.01-3

Steps to reproduce:

Create a new user with a shell of /usr/bin/bash:

useradd -m -g users -s /usr/bin/bash testuser

or

useradd -m -g users -s $(which bash) testuser

and try to login on tty1.