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From: Julien Stephan <jstephan@baylibre.com>
Date: Wed, 29 May 2024 12:07:58 +0200
Subject: [PATCH] driver: iio: add missing checks on iio_info's callback
 access
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Message-Id: <20240529-iio-core-fix-segfault-v1-1-7ff1ba881d38@baylibre.com>
To: Jonathan Cameron <jic23@kernel.org>, 
 Lars-Peter Clausen <lars@metafoo.de>
Cc: linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org, 
 Julien Stephan <jstephan@baylibre.com>

Some callbacks from iio_info structure are accessed without any check, so
if a driver doesn't implement them trying to access the corresponding
sysfs entries produce a kernel oops such as:

[ 2203.527791] Unable to handle kernel NULL pointer dereference at virtual address 00000000 when execute
[ 2203.535795] [00000000] *pgd=01e70831, *pte=00000000, *ppte=00000000
[ 2203.540822] Internal error: Oops: 80000007 [#1] PREEMPT SMP ARM
[ 2203.552078] CPU: 0 PID: 1286 Comm: cat Not tainted 6.9.0-rc5-ad7380x-mainline-g9bf895a40063-dirty #226
[ 2203.560079] Hardware name: Xilinx Zynq Platform
[ 2203.563300] PC is at 0x0
[ 2203.564523] LR is at iio_read_channel_info_avail+0x48/0xd8
[ 2203.568716] pc : [<00000000>]    lr : [<c07b52e4>]    psr: a0000013
[ 2203.573672] sp : e0bade60  ip : 5e861799  fp : 00000001
[ 2203.577586] r10: c2dcd298  r9 : 00400cc0  r8 : c2dc6000
[ 2203.581501] r7 : c4339008  r6 : c2dc6000  r5 : 00000000  r4 : c1003fc8
[ 2203.586718] r3 : e0bade70  r2 : e0bade68  r1 : bf00ac88  r0 : c4339000
[ 2203.591935] Flags: NzCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
[ 2203.597761] Control: 18c5387d  Table: 01db804a  DAC: 00000051
[ 2203.602194] Register r0 information: slab kmalloc-1k start c4339000 pointer offset 0 size 1024
[ 2203.609520] Register r1 information: 2-page vmalloc region starting at 0xbf00a000 allocated at load_module+0x704/0x1954
[ 2203.619016] Register r2 information: 2-page vmalloc region starting at 0xe0bac000 allocated at kernel_clone+0xb8/0x368
[ 2203.628417] Register r3 information: 2-page vmalloc region starting at 0xe0bac000 allocated at kernel_clone+0xb8/0x368
[ 2203.637808] Register r4 information: non-slab/vmalloc memory
[ 2203.642166] Register r5 information: NULL pointer
[ 2203.645559] Register r6 information: slab kmalloc-4k start c2dc6000 pointer offset 0 size 4096
[ 2203.652886] Register r7 information: slab kmalloc-1k start c4339000 pointer offset 8 size 1024
[ 2203.660211] Register r8 information: slab kmalloc-4k start c2dc6000 pointer offset 0 size 4096
[ 2203.667537] Register r9 information: non-paged memory
[ 2203.671278] Register r10 information: slab vm_area_struct start c2dcd280 pointer offset 24 size 80
[ 2203.678951] Register r11 information: non-paged memory
[ 2203.682779] Register r12 information: non-paged memory
[ 2203.686607] Process cat (pid: 1286, stack limit = 0x354430a3)
[ 2203.691052] Stack: (0xe0bade60 to 0xe0bae000)
[ 2203.694105] de60: e0bade6c 00000019 c105fe40 00000001 00000002 5e861799 c4309ec0 c07b529c
[ 2203.700979] de80: c411b200 c051f1e4 c0b48d30 c2dcd280 c411b200 c02c1fb8 c2dcd280 00020000
[ 2203.707853] dea0: e0badf20 c0b12d88 7ffff000 c026c944 c1003fc8 00000000 c2dcd2a8 e0badf08
[ 2203.714728] dec0: b6eaa000 c0206480 00000001 e0badfb0 c2dcda00 c1003fc8 c1e46d80 c02c0ba0
[ 2203.721602] dee0: c0b12d88 e0badf78 b6eab000 00000000 00000000 c0240114 00000a55 c1dbadb8
[ 2203.728476] df00: c1dbadb8 00000000 00000000 00000000 b6eab000 00020000 00000001 00000000
[ 2203.735342] df20: c1e46d80 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[ 2203.742208] df40: 00000000 00000000 00000000 5e861799 c1003fc8 c1003fc8 c1e46d80 00000000
[ 2203.749074] df60: 00000000 c1e46d80 b6eab000 00020000 00000000 c0240a80 00000000 00000000
[ 2203.755949] df80: 00028008 5e861799 00000003 b6f10f80 7ff00000 00000003 c01002c4 c6716e80
[ 2203.762814] dfa0: 00000003 c0100060 00000003 b6f10f80 00000003 b6eab000 00020000 00000000
[ 2203.769680] dfc0: 00000003 b6f10f80 7ff00000 00000003 00000003 00000000 00020000 00000000
[ 2203.776546] dfe0: b6e1bc88 bed80958 b6e1bc94 b6e1bcb0 60000010 00000003 00000000 00000000
[ 2203.783416] Call trace:
[ 2203.783429]  iio_read_channel_info_avail from dev_attr_show+0x18/0x48
[ 2203.789807]  dev_attr_show from sysfs_kf_seq_show+0x90/0x120
[ 2203.794181]  sysfs_kf_seq_show from seq_read_iter+0xd0/0x4e4
[ 2203.798555]  seq_read_iter from vfs_read+0x238/0x2a0
[ 2203.802236]  vfs_read from ksys_read+0xa4/0xd4
[ 2203.805385]  ksys_read from ret_fast_syscall+0x0/0x54
[ 2203.809135] Exception stack(0xe0badfa8 to 0xe0badff0)
[ 2203.812880] dfa0:                   00000003 b6f10f80 00000003 b6eab000 00020000 00000000
[ 2203.819746] dfc0: 00000003 b6f10f80 7ff00000 00000003 00000003 00000000 00020000 00000000
[ 2203.826619] dfe0: b6e1bc88 bed80958 b6e1bc94 b6e1bcb0
[ 2203.830363] Code: bad PC value
[ 2203.832695] ---[ end trace 0000000000000000 ]---

Signed-off-by: Julien Stephan <jstephan@baylibre.com>
---
 drivers/iio/industrialio-core.c  |  7 ++++++-
 drivers/iio/industrialio-event.c |  9 +++++++++
 drivers/iio/inkern.c             | 16 +++++++++++-----
 3 files changed, 26 insertions(+), 6 deletions(-)

diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
index fa7cc051b4c4..2f185b386949 100644
--- a/drivers/iio/industrialio-core.c
+++ b/drivers/iio/industrialio-core.c
@@ -758,9 +758,11 @@ static ssize_t iio_read_channel_info(struct device *dev,
 							INDIO_MAX_RAW_ELEMENTS,
 							vals, &val_len,
 							this_attr->address);
-	else
+	else if (indio_dev->info->read_raw)
 		ret = indio_dev->info->read_raw(indio_dev, this_attr->c,
 				    &vals[0], &vals[1], this_attr->address);
+	else
+		return -EINVAL;
 
 	if (ret < 0)
 		return ret;
@@ -842,6 +844,9 @@ static ssize_t iio_read_channel_info_avail(struct device *dev,
 	int length;
 	int type;
 
+	if (!indio_dev->info->read_avail)
+		return -EINVAL;
+
 	ret = indio_dev->info->read_avail(indio_dev, this_attr->c,
 					  &vals, &type, &length,
 					  this_attr->address);
diff --git a/drivers/iio/industrialio-event.c b/drivers/iio/industrialio-event.c
index 910c1f14abd5..a64f8fbac597 100644
--- a/drivers/iio/industrialio-event.c
+++ b/drivers/iio/industrialio-event.c
@@ -285,6 +285,9 @@ static ssize_t iio_ev_state_store(struct device *dev,
 	if (ret < 0)
 		return ret;
 
+	if (!indio_dev->info->write_event_config)
+		return -EINVAL;
+
 	ret = indio_dev->info->write_event_config(indio_dev,
 		this_attr->c, iio_ev_attr_type(this_attr),
 		iio_ev_attr_dir(this_attr), val);
@@ -300,6 +303,9 @@ static ssize_t iio_ev_state_show(struct device *dev,
 	struct iio_dev_attr *this_attr = to_iio_dev_attr(attr);
 	int val;
 
+	if (!indio_dev->info->read_event_config)
+		return -EINVAL;
+
 	val = indio_dev->info->read_event_config(indio_dev,
 		this_attr->c, iio_ev_attr_type(this_attr),
 		iio_ev_attr_dir(this_attr));
@@ -318,6 +324,9 @@ static ssize_t iio_ev_value_show(struct device *dev,
 	int val, val2, val_arr[2];
 	int ret;
 
+	if (!indio_dev->info->read_event_value)
+		return -EINVAL;
+
 	ret = indio_dev->info->read_event_value(indio_dev,
 		this_attr->c, iio_ev_attr_type(this_attr),
 		iio_ev_attr_dir(this_attr), iio_ev_attr_info(this_attr),
diff --git a/drivers/iio/inkern.c b/drivers/iio/inkern.c
index 52d773261828..74f87f6ac390 100644
--- a/drivers/iio/inkern.c
+++ b/drivers/iio/inkern.c
@@ -560,9 +560,11 @@ static int iio_channel_read(struct iio_channel *chan, int *val, int *val2,
 					vals, &val_len, info);
 		*val = vals[0];
 		*val2 = vals[1];
-	} else {
+	} else if (chan->indio_dev->info->read_raw) {
 		ret = chan->indio_dev->info->read_raw(chan->indio_dev,
 					chan->channel, val, val2, info);
+	} else {
+		return -EINVAL;
 	}
 
 	return ret;
@@ -753,8 +755,10 @@ static int iio_channel_read_avail(struct iio_channel *chan,
 	if (!iio_channel_has_available(chan->channel, info))
 		return -EINVAL;
 
-	return chan->indio_dev->info->read_avail(chan->indio_dev, chan->channel,
-						 vals, type, length, info);
+	if (chan->indio_dev->info->read_avail)
+		return chan->indio_dev->info->read_avail(chan->indio_dev, chan->channel,
+							 vals, type, length, info);
+	return -EINVAL;
 }
 
 int iio_read_avail_channel_attribute(struct iio_channel *chan,
@@ -917,8 +921,10 @@ EXPORT_SYMBOL_GPL(iio_get_channel_type);
 static int iio_channel_write(struct iio_channel *chan, int val, int val2,
 			     enum iio_chan_info_enum info)
 {
-	return chan->indio_dev->info->write_raw(chan->indio_dev,
-						chan->channel, val, val2, info);
+	if (chan->indio_dev->info->write_raw)
+		return chan->indio_dev->info->write_raw(chan->indio_dev,
+							chan->channel, val, val2, info);
+	return -EINVAL;
 }
 
 int iio_write_channel_attribute(struct iio_channel *chan, int val, int val2,

---
base-commit: 409b6d632f5078f3ae1018b6e43c32f2e12f6736
change-id: 20240528-iio-core-fix-segfault-aa74be7eee4a

Best regards,
-- 
Julien Stephan <jstephan@baylibre.com>