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CVE-2023-52564

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 callinggsm_dlci_release() for each available DLCI. There, dlci_put() is called todecrease the reference counter for the DLCI via tty_port_put() whichfinally calls gsm_dlci_free(). This already clears the pointer which isbeing 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 pointerdereference: ? __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 The actual issue is that nothing guards dlci_put() from being calledmultiple times while the tty driver was triggered but did not yet finishedcalling gsm_dlci_free().

POC

Reference

- http://www.openwall.com/lists/oss-security/2024/04/11/9

Github

No PoCs found on GitHub currently.