title: Revert "tty: n_gsm: fix UAF in gsm_cleanup_mux"
description: In the Linux kernel, the following vulnerability has been resolved:
Revert "tty: n_gsm: fix UAF in gsm_cleanup_mux"
This reverts commit 9b9c8195f3f0d74a826077fc1c01b9ee74907239.
The commit above is reverted as it did not solve the original issue.
gsm_cleanup_mux() tries to free up the virtual ttys by calling
gsm_dlci_release() for each available DLCI. There, dlci_put() is called to
decrease the reference counter for the DLCI via tty_port_put() which
finally calls gsm_dlci_free(). This already clears the pointer which is
being checked in gsm_cleanup_mux() before calling gsm_dlci_release().
Therefore, it is not necessary to clear this pointer in gsm_cleanup_mux()
as done in the reverted commit. The commit introduces a null pointer
dereference:
<TASK>
? __die+0x1f/0x70
? page_fault_oops+0x156/0x420
? search_exception_tables+0x37/0x50
? fixup_exception+0x21/0x310
? exc_page_fault+0x69/0x150
? asm_exc_page_fault+0x26/0x30
? tty_port_put+0x19/0xa0
gsmtty_cleanup+0x29/0x80 [n_gsm]
release_one_tty+0x37/0xe0
process_one_work+0x1e6/0x3e0
worker_thread+0x4c/0x3d0
? __pfx_worker_thread+0x10/0x10
kthread+0xe1/0x110
? __pfx_kthread+0x10/0x10
ret_from_fork+0x2f/0x50
? __pfx_kthread+0x10/0x10
ret_from_fork_asm+0x1b/0x30
</TASK>
The actual issue is that nothing guards dlci_put() from being called
multiple times while the tty driver was triggered but did not yet finished
calling gsm_dlci_free().
affected:
{
product: Linux
vendor: Linux
defaultStatus: unaffected
repo: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
versions:
version: 8fc0eabaa73b, lessThan: 6d5c8862932d, status: affected, versionType: git
version: 5138c228311a, lessThan: a48d2bcd23f2, status: affected, versionType: git
version: 9615ca54bc13, lessThan: c61d0b87a702, status: affected, versionType: git
version: 9b9c8195f3f0, lessThan: 2bff660e0ff3, status: affected, versionType: git
version: 9b9c8195f3f0, lessThan: 29346e217b8a, status: affected, versionType: git
}
{
product: Linux
vendor: Linux
defaultStatus: affected
repo: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
versions:
version: 6.5, status: affected
version: 0, lessThan: 6.5, status: unaffected, versionType: custom
version: 5.10.198, lessThanOrEqual: 5.10.*, status: unaffected, versionType: custom
version: 5.15.134, lessThanOrEqual: 5.15.*, status: unaffected, versionType: custom
version: 6.1.56, lessThanOrEqual: 6.1.*, status: unaffected, versionType: custom
version: 6.5.6, lessThanOrEqual: 6.5.*, status: unaffected, versionType: custom
version: 6.6, lessThanOrEqual: *, status: unaffected, versionType: original_commit_for_fix
}
