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Subject[PATCH] EDAC/ghes: Check whether the driver is on the safe list correctly
And here's one more I triggered with this driver removing thing:

---
From: Borislav Petkov <bp@suse.de>

With CONFIG_DEBUG_TEST_DRIVER_REMOVE=y, a system would try to probe,
unregister and probe again a driver.

When ghes_edac is attempted to be loaded on a system which is not on
the safe platforms list, ghes_edac_register() would return early. The
unregister counterpart ghes_edac_unregister() would still attempt to
unregister and exit early at the refcount test, leading to the refcount
underflow below.

In order to not do *anything* on the unregister path too, reuse the
force_load parameter and check it on that path too, before fumbling with
the refcount.

ghes_edac: ghes_edac_register: entry
ghes_edac: ghes_edac_register: return -ENODEV
------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 10 PID: 1 at lib/refcount.c:28 refcount_warn_saturate+0xb9/0x100
Modules linked in:
CPU: 10 PID: 1 Comm: swapper/0 Not tainted 5.9.0-rc4+ #12
Hardware name: GIGABYTE MZ01-CE1-00/MZ01-CE1-00, BIOS F02 08/29/2018
RIP: 0010:refcount_warn_saturate+0xb9/0x100
Code: 82 e8 fb 8f 4d 00 90 0f 0b 90 90 c3 80 3d 55 4c f5 00 00 75 88 c6 05 4c 4c f5 00 01 90 48 c7 c7 d0 8a 10 82 e8 d8 8f 4d 00 90 <0f> 0b 90 90 c3 80 3d 30 4c f5 00 00 0f 85 61 ff ff ff c6 05 23 4c
RSP: 0018:ffffc90000037d58 EFLAGS: 00010292
RAX: 0000000000000026 RBX: ffff88840b8da000 RCX: 0000000000000000
RDX: 0000000000000001 RSI: ffffffff8216b24f RDI: 00000000ffffffff
RBP: ffff88840c662e00 R08: 0000000000000001 R09: 0000000000000001
R10: 0000000000000001 R11: 0000000000000046 R12: 0000000000000000
R13: 0000000000000001 R14: 0000000000000000 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff88840ee80000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 0000800002211000 CR4: 00000000003506e0
Call Trace:
ghes_edac_unregister
ghes_remove
platform_drv_remove
really_probe
driver_probe_device
device_driver_attach
__driver_attach
? device_driver_attach
? device_driver_attach
bus_for_each_dev
bus_add_driver
driver_register
? bert_init
ghes_init
do_one_initcall
? rcu_read_lock_sched_held
kernel_init_freeable
? rest_init
kernel_init
ret_from_fork
...
ghes_edac: ghes_edac_unregister: FALSE, refcount: -1073741824

Signed-off-by: Borislav Petkov <bp@suse.de>
---
drivers/edac/ghes_edac.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/drivers/edac/ghes_edac.c b/drivers/edac/ghes_edac.c
index eb6034a6fbbb..dbbefd2798c5 100644
--- a/drivers/edac/ghes_edac.c
+++ b/drivers/edac/ghes_edac.c
@@ -508,6 +508,7 @@ int ghes_edac_register(struct ghes *ghes, struct device *dev)
if (!force_load && idx < 0)
return -ENODEV;
} else {
+ force_load = true;
idx = 0;
}

@@ -629,6 +630,9 @@ void ghes_edac_unregister(struct ghes *ghes)
struct mem_ctl_info *mci;
unsigned long flags;

+ if (!force_load)
+ return;
+
mutex_lock(&ghes_reg_mutex);

system_scanned = false;
--
2.21.0

--
Regards/Gruss,
Boris.

https://people.kernel.org/tglx/notes-about-netiquette

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