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Daniel Gibson e27376f5aa tty: n_tty: Restore EOF push handling behavior 
[ Upstream commit 65a8b28702 ]

TTYs in ICANON mode have a special case that allows "pushing" a line
without a regular EOL character (like newline), by using EOF (the EOT
character - ASCII 0x4) as a pseudo-EOL. It is silently discarded, so
the reader of the PTS will receive the line *without* EOF or any other
terminating character.

This special case has an edge case: What happens if the readers buffer
is the same size as the line (without EOF)? Will they be able to tell
if the whole line is received, i.e. if the next read() will return more
of the same line or the next line?

There are two possibilities,  that both have (dis)advantages:

1. The next read() returns 0. FreeBSD (13.0) and OSX (10.11) do this.
   Advantage: The reader can interpret this as "the line is over".
   Disadvantage: read() returning 0 means EOF, the reader could also
   interpret it as "there's no more data" and stop reading or even
   close the PT.

2. The next read() returns the next line, the EOF is silently discarded.
   Solaris (or at least OpenIndiana 2021.10) does this, Linux has done
   do this since commit 40d5e0905a ("n_tty: Fix EOF push handling");
   this behavior was recently broken by commit 3593030761 ("tty:
   n_tty: do not look ahead for EOL character past the end of the buffer").
   Advantage: read() won't return 0 (EOF), reader less likely to be
   confused (and things like `while(read(..)>0)` don't break)
   Disadvantage: The reader can't really know if the read() continues
   the last line (that filled the whole read buffer) or starts a
   new line.

As both options are defensible (and are used by other Unix-likes), it's
best to stick to the "old" behavior since "n_tty: Fix EOF push handling"
of 2013, i.e. silently discard that EOF.

This patch - that I actually got from Linus for testing and only
modified slightly - restores that behavior by skipping an EOF
character if it's the next character after reading is done.

Based on a patch from Linus Torvalds.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=215611
Fixes: 3593030761 ("tty: n_tty: do not look ahead for EOL character past the end of the buffer")
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jirislaby@kernel.org>
Reviewed-and-tested-by: Daniel Gibson <daniel@gibson.sh>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Daniel Gibson <daniel@gibson.sh>
Link: https://lore.kernel.org/r/20220329235810.452513-2-daniel@gibson.sh
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2022-06-14 18:32:30 +02:00
arch MIPS: IP30: Remove incorrect `cpu_has_fpu' override 2022-06-09 10:21:31 +02:00
block block: fix bio_clone_blkg_association() to associate with proper blkcg_gq 2022-06-09 10:21:31 +02:00
certs certs: Trigger creation of RSA module signing key if it's not an RSA key 2021-09-15 09:50:29 +02:00
crypto crypto: cryptd - Protect per-CPU resource by disabling BH. 2022-06-09 10:21:17 +02:00
Documentation dt-bindings: gpio: altera: correct interrupt-cells 2022-06-09 10:21:29 +02:00
drivers tty: n_tty: Restore EOF push handling behavior 2022-06-14 18:32:30 +02:00
fs ext4: only allow test_dummy_encryption when supported 2022-06-09 10:21:31 +02:00
include nodemask.h: fix compilation error with GCC12 2022-06-09 10:21:27 +02:00
init Kconfig: Add option for asm goto w/ tied outputs to workaround clang-13 bug 2022-06-09 10:21:25 +02:00
ipc ipc/mqueue: use get_tree_nodev() in mqueue_get_tree() 2022-06-09 10:21:17 +02:00
kernel ftrace: Clean up hash direct_functions on register failures 2022-06-09 10:21:26 +02:00
lib lib/crypto: add prompts back to crypto libraries 2022-06-06 08:42:42 +02:00
LICENSES LICENSES/deprecated: add Zlib license text 2020-09-16 14:33:49 +02:00
mm hugetlb: fix huge_pmd_unshare address update 2022-06-09 10:21:27 +02:00
net mac80211: upgrade passive scan to active scan on DFS channels after beacon rx 2022-06-09 10:21:26 +02:00
samples samples/bpf, xdpsock: Fix race when running for fix duration of time 2022-04-08 14:40:21 +02:00
scripts scripts/faddr2line: Fix overlapping text section failures 2022-06-09 10:21:08 +02:00
security ima: remove the IMA_TEMPLATE Kconfig option 2022-06-09 10:21:25 +02:00
sound ASoC: rt5514: Fix event generation for "DSP Voice Wake Up" control 2022-06-09 10:21:27 +02:00
tools kseltest/cgroup: Make test_stress.sh work if run interactively 2022-06-09 10:21:30 +02:00
usr usr/include/Makefile: add linux/nfc.h to the compile-test coverage 2022-02-01 17:25:48 +01:00
virt KVM: Prevent module exit until all VMs are freed 2022-04-08 14:40:38 +02:00
.clang-format RDMA 5.10 pull request 2020-10-17 11:18:18 -07:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore kbuild: generate Module.symvers only when vmlinux exists 2021-05-19 10:12:59 +02:00
.mailmap mailmap: add two more addresses of Uwe Kleine-König 2020-12-06 10:19:07 -08:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Jason Cooper to CREDITS 2020-11-30 10:20:34 +01:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS MAINTAINERS: add git tree for random.c 2022-05-30 09:33:24 +02:00
Makefile Linux 5.10.121 2022-06-09 10:21:31 +02:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.