From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Korsgaard Date: Sat, 29 Aug 2020 19:40:58 +0200 Subject: [Buildroot] [PATCH] fs/cpio/init: unbreak ttyname_r() on glibc after dropping /dev/console exec In-Reply-To: <20200829130911.19760-1-peter@korsgaard.com> (Peter Korsgaard's message of "Sat, 29 Aug 2020 15:09:11 +0200") References: <20200829130911.19760-1-peter@korsgaard.com> Message-ID: <87lfhxfiz9.fsf@dell.be.48ers.dk> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: buildroot@busybox.net >>>>> "Peter" == Peter Korsgaard 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 > 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 > Signed-off-by: Christian Brauner > 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 > stdin/stdout/stderr. > 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 [0]), perform this check in a subshell. > [0] https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_20_01 > Signed-off-by: Peter Korsgaard Committed to 2020.02.x and 2020.05.x, thanks. -- Bye, Peter Korsgaard