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printk: Handle pre-enabled consoles in the top-level register_console()

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The function try_enable_preferred_console() currently has the
non-obvious side effect of returning success for consoles that are
already pre-enabled. This obscures the logic flow during console
registration.

Move the check for pre-enabled consoles directly into the top-level
register_console(). This change makes the handling of pre-enabled
consoles explicit and easier to follow.

Furthermore, this separation lays the groundwork for future cleanups
where try_enable_preferred_console() can be restricted to cases where
an entry actually exists in the console_cmdline[] array.

Also it fixes a possible out-of-bound access when the console_cmdline[]
array is full and no console matched. In fact, the check of
c->user_specified did not make much sense. The new console either
matched and was handled in the for-cycle. Or it did not match
and then *c pointed to an unused entry.

Possible behavior change:

try_enable_preferred_console() will newly be called also with
@user_specified parameter set to "false" when it failed with the "true"
variant. But it looks like the right way to do. It will allow to call
newcon->setup() when the console was preferred by some platform
specific code.

Reported-by: Naveen Kumar Chaudhary <naveen.osdev@gmail.com> # out-of-bound access
Closes: https://lore.kernel.org/r/7sq4tr2nmlz32tvkf6vpsghv6exvqfghsrlvywjcqihzsqqbf7@bspclmti5xg4
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Link: https://patch.msgid.link/20260604101459.393162-2-pmladek@suse.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
This commit is contained in:
Petr Mladek 2026-06-04 12:14:48 +02:00
parent 0db1496dcb
commit 3219f9b61d
1 changed files with 8 additions and 11 deletions
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19
kernel/printk/printk.c
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@ -3890,9 +3890,6 @@ static int console_call_setup(struct console *newcon, char *options)
* the newly registered console with any of the ones selected
* by either the command line or add_preferred_console() and
* setup/enable it.
*
* Care need to be taken with consoles that are statically
* enabled such as netconsole
*/
static int try_enable_preferred_console(struct console *newcon,
bool user_specified)
@ -3933,14 +3930,6 @@ static int try_enable_preferred_console(struct console *newcon,
return 0;
}
/*
* Some consoles, such as pstore and netconsole, can be enabled even
* without matching. Accept the pre-enabled consoles only when match()
* and setup() had a chance to be called.
*/
if (newcon->flags & CON_ENABLED && c->user_specified == user_specified)
return 0;
return -ENOENT;
}
@ -4123,6 +4112,14 @@ void register_console(struct console *newcon)
if (err == -ENOENT)
err = try_enable_preferred_console(newcon, false);
/*
* Some consoles, such as pstore and netconsole, can be enabled even
* without matching. Accept them at this stage when they had a chance
* to match() and call setup().
*/
if (err == -ENOENT && (newcon->flags & CON_ENABLED))
err = 0;
/* printk() messages are not printed to the Braille console. */
if (err || newcon->flags & CON_BRL) {
if (newcon->flags & CON_NBCON)