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/proc/sysrq-trigger: accept multiple keys at once

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This way we can do:
`echo _reisub > /proc/sysrq-trigger`
Instead of:
`for i in r e i s u b; do echo "$i" > /proc/sysrq-trigger; done;`

This can be very useful when trying to execute sysrq combo remotely
or from userspace. When sending keys in multiple separate writes,
userspace (eg. bash or ssh) can be killed before whole combo is completed.
Therefore putting all keys in single write is more robust approach.

Signed-off-by: Tomas Mudrunka <tomas.mudrunka@gmail.com>
Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20231120111451.527952-1-tomas.mudrunka@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Tomas Mudrunka 2023-11-20 12:14:51 +01:00 committed by Greg Kroah-Hartman
parent 01c33b8138
commit 39ff20f5fd
2 changed files with 26 additions and 4 deletions
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11
Documentation/admin-guide/sysrq.rst
View File

@ -75,10 +75,19 @@ On other
submit a patch to be included in this section.
On all
Write a character to /proc/sysrq-trigger. e.g.::
Write a single character to /proc/sysrq-trigger.
Only the first character is processed, the rest of the string is
ignored. However, it is not recommended to write any extra characters
as the behavior is undefined and might change in the future versions.
E.g.::
echo t > /proc/sysrq-trigger
Alternatively, write multiple characters prepended by underscore.
This way, all characters will be processed. E.g.::
echo _reisub > /proc/sysrq-trigger
The :kbd:`<command key>` is case sensitive.
What are the 'command' keys?

17
drivers/tty/sysrq.c
View File

@ -1150,16 +1150,29 @@ EXPORT_SYMBOL(unregister_sysrq_key);
#ifdef CONFIG_PROC_FS
/*
* writing 'C' to /proc/sysrq-trigger is like sysrq-C
* Normally, only the first character written is processed.
* However, if the first character is an underscore,
* all characters are processed.
*/
static ssize_t write_sysrq_trigger(struct file *file, const char __user *buf,
size_t count, loff_t *ppos)
{
if (count) {
bool bulk = false;
size_t i;
for (i = 0; i < count; i++) {
char c;
if (get_user(c, buf))
if (get_user(c, buf + i))
return -EFAULT;
if (c == '_')
bulk = true;
else
__handle_sysrq(c, false);
if (!bulk)
break;
}
return count;