[PATCH] §tools: iio: iio_generic_buffer: Fix read size

[Matti Vaittinen]

When noevents is true and small buffer is used the allocated memory for
holding the data may be smaller than the hard-coded 64 bytes. This can
cause the iio_generic_buffer to crash.

Following was recorded on beagle bone black with v6.0 kernel and the
digit fix patch:
https://lore.kernel.org/all/Y0f+tKCz+ZAIoroQ@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
using valgrind;

==339== Using Valgrind-3.18.1 and LibVEX; rerun with -h for copyright info
==339== Command: /iio_generic_buffer -n kx022-accel -T0 -e -l 10 -a -w 2000000
==339== Parent PID: 307
==339==
==339== Syscall param read(buf) points to unaddressable byte(s)
==339==    at 0x496BFA4: read (read.c:26)
==339==    by 0x11699: main (iio_generic_buffer.c:724)
==339==  Address 0x4ab3518 is 0 bytes after a block of size 160 alloc'd
==339==    at 0x4864B70: malloc (vg_replace_malloc.c:381)
==339==    by 0x115BB: main (iio_generic_buffer.c:677)

Fix this by always using the same size for reading as was used for
data storage allocation.

Signed-off-by: Matti Vaittinen <mazziesaccount@xxxxxxxxx>

---

This patch has been only tested with my kx022a sensor driver. Driver may
have some culprits(s) and my understanding regarding IIO and these tools
is limited so perhaps the hard-coded size of 64 bytes has perfectly
legitimate reason - in which case I would appreciate to hear the
reasoning so I could seek the problem from my driver. Also, I didn't add
the fixes-tag as I don't really know which commit has caused the problem
- as I am not 100% sure what the problem actually is and if I am just
fixing a symptom here.
---
 tools/iio/iio_generic_buffer.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/iio/iio_generic_buffer.c b/tools/iio/iio_generic_buffer.c
index 2491c54a5e4f..f8deae4e26a1 100644
--- a/tools/iio/iio_generic_buffer.c
+++ b/tools/iio/iio_generic_buffer.c
@@ -715,12 +715,12 @@ int main(int argc, char **argv)
 				continue;
 			}
 
-			toread = buf_len;
 		} else {
 			usleep(timedelay);
-			toread = 64;
 		}
 
+		toread = buf_len;
+
 		read_size = read(buf_fd, data, toread * scan_size);
 		if (read_size < 0) {
 			if (errno == EAGAIN) {

base-commit: 4fe89d07dcc2804c8b562f6c7896a45643d34b2f
-- 
2.37.3


-- 
Matti Vaittinen, Linux device drivers
ROHM Semiconductors, Finland SWDC
Kiviharjunlenkki 1E
90220 OULU
FINLAND

~~~ "I don't think so," said Rene Descartes. Just then he vanished ~~~
Simon says - in Latin please.
~~~ "non cogito me" dixit Rene Descarte, deinde evanescavit ~~~
Thanks to Simon Glass for the translation =]

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