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Subject[PATCH 4.4 025/135] drivers: base: Fix NULL pointer exception in __platform_driver_probe() if a driver developer is foolish
Date
From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

[ Upstream commit 388bcc6ecc609fca1b4920de7dc3806c98ec535e ]

If platform bus driver registration is failed then, accessing
platform bus spin lock (&drv->driver.bus->p->klist_drivers.k_lock)
in __platform_driver_probe() without verifying the return value
__platform_driver_register() can lead to NULL pointer exception.

So check the return value before attempting the spin lock.

One such example is below:

For a custom usecase, I have intentionally failed the platform bus
registration and I expected all the platform device/driver
registrations to fail gracefully. But I came across this panic
issue.

[ 1.331067] BUG: kernel NULL pointer dereference, address: 00000000000000c8
[ 1.331118] #PF: supervisor write access in kernel mode
[ 1.331163] #PF: error_code(0x0002) - not-present page
[ 1.331208] PGD 0 P4D 0
[ 1.331233] Oops: 0002 [#1] PREEMPT SMP
[ 1.331268] CPU: 3 PID: 1 Comm: swapper/0 Tainted: G W 5.6.0-00049-g670d35fb0144 #165
[ 1.331341] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
[ 1.331406] RIP: 0010:_raw_spin_lock+0x15/0x30
[ 1.331588] RSP: 0000:ffffc9000001be70 EFLAGS: 00010246
[ 1.331632] RAX: 0000000000000000 RBX: 00000000000000c8 RCX: 0000000000000001
[ 1.331696] RDX: 0000000000000001 RSI: 0000000000000092 RDI: 0000000000000000
[ 1.331754] RBP: 00000000ffffffed R08: 0000000000000501 R09: 0000000000000001
[ 1.331817] R10: ffff88817abcc520 R11: 0000000000000670 R12: 00000000ffffffed
[ 1.331881] R13: ffffffff82dbc268 R14: ffffffff832f070a R15: 0000000000000000
[ 1.331945] FS: 0000000000000000(0000) GS:ffff88817bd80000(0000) knlGS:0000000000000000
[ 1.332008] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1.332062] CR2: 00000000000000c8 CR3: 000000000681e001 CR4: 00000000003606e0
[ 1.332126] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 1.332189] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 1.332252] Call Trace:
[ 1.332281] __platform_driver_probe+0x92/0xee
[ 1.332323] ? rtc_dev_init+0x2b/0x2b
[ 1.332358] cmos_init+0x37/0x67
[ 1.332396] do_one_initcall+0x7d/0x168
[ 1.332428] kernel_init_freeable+0x16c/0x1c9
[ 1.332473] ? rest_init+0xc0/0xc0
[ 1.332508] kernel_init+0x5/0x100
[ 1.332543] ret_from_fork+0x1f/0x30
[ 1.332579] CR2: 00000000000000c8
[ 1.332616] ---[ end trace 3bd87f12e9010b87 ]---
[ 1.333549] note: swapper/0[1] exited with preempt_count 1
[ 1.333592] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000009
[ 1.333736] Kernel Offset: disabled

Note, this can only be triggered if a driver errors out from this call,
which should never happen. If it does, the driver needs to be fixed.

Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Link: https://lore.kernel.org/r/20200408214003.3356-1-sathyanarayanan.kuppuswamy@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/base/platform.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/base/platform.c b/drivers/base/platform.c
index 065fcc4be263a..f89cb143f1cdf 100644
--- a/drivers/base/platform.c
+++ b/drivers/base/platform.c
@@ -638,6 +638,8 @@ int __init_or_module __platform_driver_probe(struct platform_driver *drv,
/* temporary section violation during probe() */
drv->probe = probe;
retval = code = __platform_driver_register(drv, module);
+ if (retval)
+ return retval;

/*
* Fixup that section violation, being paranoid about code scanning
--
2.25.1
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