kdb: Fix buffer overflow during tab-complete

stable inclusion
from stable-v4.19.316
commit fb824a99e148ff272a53d71d84122728b5f00992
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/IAB05N
CVE: CVE-2024-39480

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fb824a99e148ff272a53d71d84122728b5f00992



--------------------------------

commit e9730744bf3af04cda23799029342aa3cddbc454 upstream.

Currently, when the user attempts symbol completion with the Tab key, kdb
will use strncpy() to insert the completed symbol into the command buffer.
Unfortunately it passes the size of the source buffer rather than the
destination to strncpy() with predictably horrible results. Most obviously
if the command buffer is already full but cp, the cursor position, is in
the middle of the buffer, then we will write past the end of the supplied
buffer.

Fix this by replacing the dubious strncpy() calls with memmove()/memcpy()
calls plus explicit boundary checks to make sure we have enough space
before we start moving characters around.

Reported-by: Justin Stitt <justinstitt@google.com>
Closes: https://lore.kernel.org/all/CAFhGd8qESuuifuHsNjFPR-Va3P80bxrw+LqvC8deA8GziUJLpw@mail.gmail.com/


Cc: stable@vger.kernel.org
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Justin Stitt <justinstitt@google.com>
Tested-by: Justin Stitt <justinstitt@google.com>
Link: https://lore.kernel.org/r/20240424-kgdb_read_refactor-v3-1-f236dbe9828d@linaro.org


Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Fixes: 5d5314d6 ("kdb: core for kgdb back end (1 of 2)")
Signed-off-by: Tengda Wu <wutengda2@huawei.com>