tree 2a0c40ddb0b8f87c663efb20bd1394b3099c5bc1
parent 3a2d7dc6f4f2cd5eed2effa50275015af2117b03
author Thomas Gleixner <tglx@linutronix.de> 1725440947 +0200
committer Kevin Berry <kpberry@google.com> 1730762182 +0000

static_call: Handle module init failure correctly in static_call_del_module()

[ Upstream commit 4b30051c4864234ec57290c3d142db7c88f10d8a ]

Module insertion invokes static_call_add_module() to initialize the static
calls in a module. static_call_add_module() invokes __static_call_init(),
which allocates a struct static_call_mod to either encapsulate the built-in
static call sites of the associated key into it so further modules can be
added or to append the module to the module chain.

If that allocation fails the function returns with an error code and the
module core invokes static_call_del_module() to clean up eventually added
static_call_mod entries.

This works correctly, when all keys used by the module were converted over
to a module chain before the failure. If not then static_call_del_module()
causes a #GP as it blindly assumes that key::mods points to a valid struct
static_call_mod.

The problem is that key::mods is not a individual struct member of struct
static_call_key, it's part of a union to save space:

        union {
                /* bit 0: 0 = mods, 1 = sites */
                unsigned long type;
                struct static_call_mod *mods;
                struct static_call_site *sites;
	};

key::sites is a pointer to the list of built-in usage sites of the static
call. The type of the pointer is differentiated by bit 0. A mods pointer
has the bit clear, the sites pointer has the bit set.

As static_call_del_module() blidly assumes that the pointer is a valid
static_call_mod type, it fails to check for this failure case and
dereferences the pointer to the list of built-in call sites, which is
obviously bogus.

Cure it by checking whether the key has a sites or a mods pointer.

If it's a sites pointer then the key is not to be touched. As the sites are
walked in the same order as in __static_call_init() the site walk can be
terminated because all subsequent sites have not been touched by the init
code due to the error exit.

If it was converted before the allocation fail, then the inner loop which
searches for a module match will find nothing.

A fail in the second allocation in __static_call_init() is harmless and
does not require special treatment. The first allocation succeeded and
converted the key to a module chain. That first entry has mod::mod == NULL
and mod::next == NULL, so the inner loop of static_call_del_module() will
neither find a module match nor a module chain. The next site in the walk
was either already converted, but can't match the module, or it will exit
the outer loop because it has a static_call_site pointer and not a
static_call_mod pointer.

BUG=b/377000327
TEST=presubmit
RELEASE_NOTE=Fixed CVE-2024-50002 in the Linux kernel.

cos-patch: security-moderate
Fixes: 9183c3f9ed71 ("static_call: Add inline static call infrastructure")
Closes: https://lore.kernel.org/all/20230915082126.4187913-1-ruanjinjie@huawei.com
Reported-by: Jinjie Ruan <ruanjinjie@huawei.com>
Change-Id: I252b65ff78af872ce5ce3779ba8571fcedb20be2
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Jinjie Ruan <ruanjinjie@huawei.com>
Link: https://lore.kernel.org/r/87zfon6b0s.ffs@tglx
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kernel CVE Triage Automation <cloud-image-kernel-cve-triage-automation@prod.google.com>
Reviewed-on: https://cos-review.googlesource.com/c/third_party/kernel/+/85182
Reviewed-by: Shuo Yang <gshuoy@google.com>
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Reviewed-by: Kevin Berry <kpberry@google.com>