* [Buildroot] [PATCH] fs/cpio/init: unbreak ttyname_r() on glibc after dropping /dev/console exec
2020-08-29 13:09 [Buildroot] [PATCH] fs/cpio/init: unbreak ttyname_r() on glibc after dropping /dev/console exec Peter Korsgaard
@ 2020-08-29 13:24 ` Yann E. MORIN
2020-08-29 13:40 ` Peter Korsgaard
2020-08-29 14:43 ` Yann E. MORIN
2020-08-29 17:40 ` Peter Korsgaard
2 siblings, 1 reply; 5+ messages in thread
From: Yann E. MORIN @ 2020-08-29 13:24 UTC (permalink / raw)
To: buildroot
Peter, All,
On 2020-08-29 15:09 +0200, Peter Korsgaard spake thusly:
> 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@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@hallyn.com>
> Signed-off-by: Christian Brauner <christian.brauner@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@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
You forgot the else part, which should redirect to /dev/null, so that we
do have valid fds in the case /dev/console does not really exist, no?
Regards,
Yann E. MORIN.
> exec /sbin/init "$@"
> --
> 2.20.1
>
--
.-----------------.--------------------.------------------.--------------------.
| Yann E. MORIN | Real-Time Embedded | /"\ ASCII RIBBON | Erics' conspiracy: |
| +33 662 376 056 | Software Designer | \ / CAMPAIGN | ___ |
| +33 561 099 427 `------------.-------: X AGAINST | \e/ There is no |
| http://ymorin.is-a-geek.org/ | _/*\_ | / \ HTML MAIL | v conspiracy. |
'------------------------------^-------^------------------^--------------------'
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Buildroot] [PATCH] fs/cpio/init: unbreak ttyname_r() on glibc after dropping /dev/console exec
2020-08-29 13:24 ` Yann E. MORIN
@ 2020-08-29 13:40 ` Peter Korsgaard
0 siblings, 0 replies; 5+ messages in thread
From: Peter Korsgaard @ 2020-08-29 13:40 UTC (permalink / raw)
To: buildroot
>>>>> "Yann" == Yann E MORIN <yann.morin.1998@free.fr> writes:
Hi,
>> +# 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
> You forgot the else part, which should redirect to /dev/null, so that we
> do have valid fds in the case /dev/console does not really exist, no?
Well, the kernel already takes care of that since commit 2bd3a997befc2
(E.G. as explained by buildroot commit 98a6f1fc02e41), so I am not sure
what explicitly reopening /dev/null would achive?
ttyname_r() / tty already returns ENOENT (not a tty) for this case
without reopening /dev/null:
tty </dev/null
not a tty
--
Bye, Peter Korsgaard
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Buildroot] [PATCH] fs/cpio/init: unbreak ttyname_r() on glibc after dropping /dev/console exec
2020-08-29 13:09 [Buildroot] [PATCH] fs/cpio/init: unbreak ttyname_r() on glibc after dropping /dev/console exec Peter Korsgaard
2020-08-29 13:24 ` Yann E. MORIN
@ 2020-08-29 14:43 ` Yann E. MORIN
2020-08-29 17:40 ` Peter Korsgaard
2 siblings, 0 replies; 5+ messages in thread
From: Yann E. MORIN @ 2020-08-29 14:43 UTC (permalink / raw)
To: buildroot
Peter, All,
On 2020-08-29 15:09 +0200, Peter Korsgaard spake thusly:
> 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@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@hallyn.com>
> Signed-off-by: Christian Brauner <christian.brauner@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@korsgaard.com>
Applied to master, thanks.
Regards,
Yann E. MORIN.
> ---
> 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 "$@"
> --
> 2.20.1
>
--
.-----------------.--------------------.------------------.--------------------.
| Yann E. MORIN | Real-Time Embedded | /"\ ASCII RIBBON | Erics' conspiracy: |
| +33 662 376 056 | Software Designer | \ / CAMPAIGN | ___ |
| +33 561 099 427 `------------.-------: X AGAINST | \e/ There is no |
| http://ymorin.is-a-geek.org/ | _/*\_ | / \ HTML MAIL | v conspiracy. |
'------------------------------^-------^------------------^--------------------'
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Buildroot] [PATCH] fs/cpio/init: unbreak ttyname_r() on glibc after dropping /dev/console exec
2020-08-29 13:09 [Buildroot] [PATCH] fs/cpio/init: unbreak ttyname_r() on glibc after dropping /dev/console exec Peter Korsgaard
2020-08-29 13:24 ` Yann E. MORIN
2020-08-29 14:43 ` Yann E. MORIN
@ 2020-08-29 17:40 ` Peter Korsgaard
2 siblings, 0 replies; 5+ messages in thread
From: Peter Korsgaard @ 2020-08-29 17:40 UTC (permalink / raw)
To: buildroot
>>>>> "Peter" == Peter Korsgaard <peter@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@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@hallyn.com>
> Signed-off-by: Christian Brauner <christian.brauner@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@korsgaard.com>
Committed to 2020.02.x and 2020.05.x, thanks.
--
Bye, Peter Korsgaard
^ permalink raw reply [flat|nested] 5+ messages in thread