[Buildroot] [git commit branch/2020.02.x] fs/cpio/init: unbreak ttyname_r() on glibc after dropping /dev/console exec
Peter Korsgaard
peter at korsgaard.com
Sat Aug 29 17:40:49 UTC 2020
commit: https://git.buildroot.net/buildroot/commit/?id=f1a83afe2df2a72a35e32449a392532df7c3014f
branch: https://git.buildroot.net/buildroot/commit/?id=refs/heads/2020.02.x
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
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 <peter at korsgaard.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998 at free.fr>
(cherry picked from commit b9026e83f9c7610526f045f2fc1135b45a26305f)
Signed-off-by: Peter Korsgaard <peter at korsgaard.com>
---
fs/cpio/init | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/fs/cpio/init b/fs/cpio/init
index b0af18b67a..f74ef7e15f 100755
--- a/fs/cpio/init
+++ b/fs/cpio/init
@@ -1,4 +1,15 @@
#!/bin/sh
# devtmpfs does not get automounted for initramfs
/bin/mount -t devtmpfs devtmpfs /dev
+
+# use the /dev/console device node from devtmpfs if possible to not
+# confuse glibc's ttyname_r().
+# This may fail (E.G. booted with console=), and errors from exec will
+# terminate the shell, so use a subshell for the test
+if (exec 0</dev/console) 2>/dev/null; then
+ exec 0</dev/console
+ exec 1>/dev/console
+ exec 2>/dev/console
+fi
+
exec /sbin/init "$@"
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