[Buildroot] [PATCH] fs/cpio/init: unbreak ttyname_r() on glibc after dropping /dev/console exec
peter at korsgaard.com
Sat Aug 29 17:40:58 UTC 2020
>>>>> "Peter" == Peter Korsgaard <peter at korsgaard.com> writes:
> Commit 98a6f1fc02e41 (fs/cpio: make initramfs init script survive 'console='
> kernel argument) dropped the explicit /dev/console execs for fd 0,1,2, as
> they fail when booted with console= and aren't really needed as the kernel
> will setup fd 0,1,2 from /dev/console before executing the initramfs anyway.
> Not doing this unfortunately confuses glibc's ttyname_r(3) implementation
> (used by E.G. busybox/coreutils 'tty'), causing it to fail with ENOENT as
> it does a fstat on fd 0 and tries to match up st_ino / st_dev against the
> entries in /dev (since glibc 2.26):
> commit 15e9a4f378c8607c2ae1aa465436af4321db0e23
> Author: Christian Brauner <christian.brauner at canonical.com>
> Date: Fri Jan 27 15:59:59 2017 +0100
> linux ttyname and ttyname_r: do not return wrong results
> If a link (say /proc/self/fd/0) pointing to a device, say /dev/pts/2, in a
> parent mount namespace is passed to ttyname, and a /dev/pts/2 exists (in a
> different devpts) in the current namespace, then it returns /dev/pts/2.
> But /dev/pts/2 is NOT the current tty, it is a different file and device.
> Detect this case and return ENODEV. Userspace can choose to take this as a hint
> that the fd points to a tty device but to act on the fd rather than the link.
> Signed-off-by: Serge Hallyn <serge at hallyn.com>
> Signed-off-by: Christian Brauner <christian.brauner at ubuntu.com>
> The reason it fails is that we manually mount devtmpfs on /dev in /init, so
> the /dev/console used by the kernel (in rootfs) is not the same file as
> /dev/console at runtime (in devtmpfs).
> Notice: Once logged in, tty does work correctly. Presumably login reopens
> To fix this, re-add the exec of /dev/console for fd 0,1,2, but only do so if
> possible. Because of the above mentioned shell behaviour (specified by
> POSIX ), perform this check in a subshell.
>  https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_20_01
> Signed-off-by: Peter Korsgaard <peter at korsgaard.com>
Committed to 2020.02.x and 2020.05.x, thanks.
Bye, Peter Korsgaard
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