speakup: keyhelp: guard letter_offsets possible out-of-range indexing

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help_init() builds letter_offsets[] by using the first byte of each
function name as an index via `(start & 31) - 1`. If function_names are
overridden from sysfs (root) with a name starting outside [a–z], the
index underflows or exceeds the array, leading to OOB write.

Function names can be overridden with the following commands as root:

    modprobe speakup_soft
    echo "0 _bad" > /sys/accessibility/speakup/i18n/function_names
    # then press Insert+2 on /dev/tty

This fix checks the first letter in help_init(), and if it is not in the
[a–z] range the function returns an error to the caller. Eventually this
error is propagated to drivers/accessibility/speakup/main.c:2217, which
causes a bleep sound.

Fixes: c6e3fd22cd ("Staging: add speakup to the staging directory")
Signed-off-by: Pavel Zhigulin <Pavel.Zhigulin@kaspersky.com>
Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Link: https://patch.msgid.link/20260531230804.254962-10-samuel.thibault@ens-lyon.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

...

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Pavel Zhigulin 2026-06-01 01:07:58 +02:00 • committed by Greg Kroah-Hartman

parent 768ce60dc8

commit 6a19ad4d68

1 changed files with 12 additions and 5 deletions

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drivers/accessibility/speakup/keyhelp.c

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