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().
[
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "8fc0eabaa73b",
"lessThan": "6d5c8862932d",
"versionType": "git"
},
{
"status": "affected",
"version": "5138c228311a",
"lessThan": "a48d2bcd23f2",
"versionType": "git"
},
{
"status": "affected",
"version": "9615ca54bc13",
"lessThan": "c61d0b87a702",
"versionType": "git"
},
{
"status": "affected",
"version": "9b9c8195f3f0",
"lessThan": "2bff660e0ff3",
"versionType": "git"
},
{
"status": "affected",
"version": "9b9c8195f3f0",
"lessThan": "29346e217b8a",
"versionType": "git"
}
],
"programFiles": [
"drivers/tty/n_gsm.c"
],
"defaultStatus": "unaffected"
},
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "6.5"
},
{
"status": "unaffected",
"version": "0",
"lessThan": "6.5",
"versionType": "custom"
},
{
"status": "unaffected",
"version": "5.10.198",
"versionType": "custom",
"lessThanOrEqual": "5.10.*"
},
{
"status": "unaffected",
"version": "5.15.134",
"versionType": "custom",
"lessThanOrEqual": "5.15.*"
},
{
"status": "unaffected",
"version": "6.1.56",
"versionType": "custom",
"lessThanOrEqual": "6.1.*"
},
{
"status": "unaffected",
"version": "6.5.6",
"versionType": "custom",
"lessThanOrEqual": "6.5.*"
},
{
"status": "unaffected",
"version": "6.6",
"versionType": "original_commit_for_fix",
"lessThanOrEqual": "*"
}
],
"programFiles": [
"drivers/tty/n_gsm.c"
],
"defaultStatus": "affected"
}
]
git.kernel.org/stable/c/29346e217b8ab8a52889b88f00b268278d6b7668
git.kernel.org/stable/c/2bff660e0ff349dee84dc4f6f6d10da4497f5b28
git.kernel.org/stable/c/6d5c8862932d31a810b6545f7d69ecc124402c6e
git.kernel.org/stable/c/a48d2bcd23f2c98d575bc2f9b7a3fbd16aeea9eb
git.kernel.org/stable/c/c61d0b87a7028c2c10faffc524d748334c7b9827