On 18/05/17 08:12, Marcin Niestroj wrote:
In case oldtrig == trig == NULL (which happens when we set none
trigger, when there is already none set) there is a NULL pointer
dereference during iio_trigger_put(trig). Below is kernel output when
this occurs:
[ 26.741790] Unable to handle kernel NULL pointer dereference at virtual address 00000000
[ 26.750179] pgd = cacc0000
[ 26.752936] [00000000] *pgd=8adc6835, *pte=00000000, *ppte=00000000
[ 26.759531] Internal error: Oops: 17 [#1] SMP ARM
[ 26.764261] Modules linked in: usb_f_ncm u_ether usb_f_acm u_serial usb_f_fs libcomposite configfs evbug
[ 26.773844] CPU: 0 PID: 152 Comm: synchro Not tainted 4.12.0-rc1 #2
[ 26.780128] Hardware name: Freescale i.MX6 Ultralite (Device Tree)
[ 26.786329] task: cb1de200 task.stack: cac92000
[ 26.790892] PC is at iio_trigger_write_current+0x188/0x1f4
[ 26.796403] LR is at lock_release+0xf8/0x20c
[ 26.800696] pc : [<c0736f34>] lr : [<c016efb0>] psr: 600d0013
[ 26.800696] sp : cac93e30 ip : cac93db0 fp : cac93e5c
[ 26.812193] r10: c0e64fe8 r9 : 00000000 r8 : 00000001
[ 26.817436] r7 : cb190810 r6 : 00000010 r5 : 00000001 r4 : 00000000
[ 26.823982] r3 : 00000000 r2 : 00000000 r1 : cb1de200 r0 : 00000000
[ 26.830528] Flags: nZCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment none
[ 26.837683] Control: 10c5387d Table: 8acc006a DAC: 00000051
[ 26.843448] Process synchro (pid: 152, stack limit = 0xcac92210)
[ 26.849475] Stack: (0xcac93e30 to 0xcac94000)
[ 26.853857] 3e20: 00000001 c0736dac c054033c cae6b680
[ 26.862060] 3e40: cae6b680 00000000 00000001 cb3f8610 cac93e74 cac93e60 c054035c c0736db8
[ 26.870264] 3e60: 00000001 c054033c cac93e94 cac93e78 c029bf34 c0540348 00000000 00000000
[ 26.878469] 3e80: cb3f8600 cae6b680 cac93ed4 cac93e98 c029b320 c029bef0 00000000 00000000
[ 26.886672] 3ea0: 00000000 cac93f78 cb2d41fc caed3280 c029b214 cac93f78 00000001 000e20f8
[ 26.894874] 3ec0: 00000001 00000000 cac93f44 cac93ed8 c0221dcc c029b220 c0e1ca39 cb2d41fc
[ 26.903079] 3ee0: cac93f04 cac93ef0 c0183ef0 c0183ab0 cb2d41fc 00000000 cac93f44 cac93f08
[ 26.911282] 3f00: c0225eec c0183ebc 00000001 00000000 c0223728 00000000 c0245454 00000001
[ 26.919485] 3f20: 00000001 caed3280 000e20f8 cac93f78 000e20f8 00000001 cac93f74 cac93f48
[ 26.927690] 3f40: c0223680 c0221da4 c0246520 c0245460 caed3283 caed3280 00000000 00000000
[ 26.935893] 3f60: 000e20f8 00000001 cac93fa4 cac93f78 c0224520 c02235e4 00000000 00000000
[ 26.944096] 3f80: 00000001 000e20f8 00000001 00000004 c0107f84 cac92000 00000000 cac93fa8
[ 26.952299] 3fa0: c0107de0 c02244e8 00000001 000e20f8 0000000e 000e20f8 00000001 fbad2484
[ 26.960502] 3fc0: 00000001 000e20f8 00000001 00000004 beb6b698 00064260 0006421c beb6b4b4
[ 26.968705] 3fe0: 00000000 beb6b450 b6f219a0 b6e2f268 800d0010 0000000e cac93ff4 cac93ffc
[ 26.976896] Backtrace:
[ 26.979388] [<c0736dac>] (iio_trigger_write_current) from [<c054035c>] (dev_attr_store+0x20/0x2c)
[ 26.988289] r10:cb3f8610 r9:00000001 r8:00000000 r7:cae6b680 r6:cae6b680 r5:c054033c
[ 26.996138] r4:c0736dac r3:00000001
[ 26.999747] [<c054033c>] (dev_attr_store) from [<c029bf34>] (sysfs_kf_write+0x50/0x54)
[ 27.007686] r5:c054033c r4:00000001
[ 27.011290] [<c029bee4>] (sysfs_kf_write) from [<c029b320>] (kernfs_fop_write+0x10c/0x224)
[ 27.019579] r7:cae6b680 r6:cb3f8600 r5:00000000 r4:00000000
[ 27.025271] [<c029b214>] (kernfs_fop_write) from [<c0221dcc>] (__vfs_write+0x34/0x120)
[ 27.033214] r10:00000000 r9:00000001 r8:000e20f8 r7:00000001 r6:cac93f78 r5:c029b214
[ 27.041059] r4:caed3280
[ 27.043622] [<c0221d98>] (__vfs_write) from [<c0223680>] (vfs_write+0xa8/0x170)
[ 27.050959] r9:00000001 r8:000e20f8 r7:cac93f78 r6:000e20f8 r5:caed3280 r4:00000001
[ 27.058731] [<c02235d8>] (vfs_write) from [<c0224520>] (SyS_write+0x44/0x98)
[ 27.065806] r9:00000001 r8:000e20f8 r7:00000000 r6:00000000 r5:caed3280 r4:caed3283
[ 27.073582] [<c02244dc>] (SyS_write) from [<c0107de0>] (ret_fast_syscall+0x0/0x1c)
[ 27.081179] r9:cac92000 r8:c0107f84 r7:00000004 r6:00000001 r5:000e20f8 r4:00000001
[ 27.088947] Code: 1a000009 e1a04009 e3a06010 e1a05008 (e5943000)
[ 27.095244] ---[ end trace 06d1dab86d6e6bab ]---
To fix that problem call iio_trigger_put(trig) only when trig is not
NULL.
Fixes: d5d24bcc0a10 ("iio: trigger: close race condition in acquiring trigger reference")
Signed-off-by: Marcin Niestroj <m.niestroj@xxxxxxxxxxxxxxxx>
Good catch. Applied to the fixes-togreg branch of iio.git.
Thanks,
Jonathan
---
drivers/iio/industrialio-trigger.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/iio/industrialio-trigger.c b/drivers/iio/industrialio-trigger.c
index 978e1592c2a3..4061fed93f1f 100644
--- a/drivers/iio/industrialio-trigger.c
+++ b/drivers/iio/industrialio-trigger.c
@@ -451,7 +451,8 @@ static ssize_t iio_trigger_write_current(struct device *dev,
return len;
out_trigger_put:
- iio_trigger_put(trig);
+ if (trig)
+ iio_trigger_put(trig);
return ret;
}
--
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