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From: Marcelo Diop-Gonzalez <marcgonzalez@google.com>
To: gregkh@linuxfoundation.org, eric@anholt.net, wahrenst@gmx.net
Cc: devel@driverdev.osuosl.org, linux-rpi-kernel@lists.infradead.org
Subject: [PATCH v2 0/4] staging: vchiq: Fix vchiq_read return value in case of error
Date: Wed, 20 Nov 2019 15:20:58 -0500
Message-ID: <20191120202102.249121-1-marcgonzalez@google.com> (raw)
In-Reply-To: <cover.1574253964.git.marcgonzalez@google.com>

This is a proposed fix of an issue regarding the handling of positive
return values from copy_to_user() in vchiq_read(). It looks like the
struct dump_context passed to the vchiq_dump() function keeps track
of the number of bytes written in the context->actual field. When
copy_to_user() returns a positive value, this is set to -EFAULT. The
problem is that this is never returned to the user, and instead the
function continues, adding the number of bytes that should have
been copied to context->actual.

Running the following program:

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>

int main(int argc, char **argv) {
        int fd = open("/dev/vchiq", 0);
        if (fd < 0)
                exit(-1);
        sbrk(getpagesize());
        char *bad_buf = sbrk(0)-100;
        int x = read(fd, bad_buf, 2000);
        printf("%d %d\n", x, errno);
        puts(bad_buf);
}

gives this output:

-1 1
State 0: CONNECTED
  tx_po


  Remote: slots 2-32 tx_pos=578 recycle=1f
    Slots claimed:

Note the mangled output and incorrect errno value. Messing with the
constants in that toy program changes the results. Sometimes read()
returns with no error, sometimes it returns with a wrong error code,
sometimes with the right one. But it seems that it only ever returns an
error at all accidentally, due to the fact that the comparison between
context->actual and context->space in vchiq_dump() is unsigned, so that
that function won't do anything else if it ever sets context->actual
to a negative value.

After this patchset, the above program prints this:

-1 14
State 0: CONNECTED
  tx_pos=b4a218(@165de6b4), rx_pos=ae0668(@f02b54f4)
  Version: 8 (min 3)
  Stats

Help with testing would be appreciated. So far I've basically just
diffed the output of 'cat /dev/vchiq', run the program above with
a few different values, and run vchiq_test a few times.

These were applied to the staging-next branch of the tree
at git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git

v2:
separate first patch into different logical changes.

Marcelo Diop-Gonzalez (4):
  staging: vchiq: Fix block comment format in vchiq_dump()
  staging: vchiq_dump: Replace min with min_t
  staging: vchiq: Refactor indentation in vchiq_dump_* functions
  staging: vchiq: Have vchiq_dump_* functions return an error code

 .../interface/vchiq_arm/vchiq_2835_arm.c      |   5 +-
 .../interface/vchiq_arm/vchiq_arm.c           | 129 ++++++++++--------
 .../interface/vchiq_arm/vchiq_core.c          | 104 ++++++++++----
 .../interface/vchiq_arm/vchiq_core.h          |  12 +-
 4 files changed, 153 insertions(+), 97 deletions(-)

-- 
2.24.0.432.g9d3f5f5b63-goog

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Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-20 15:36 [PATCH 0/3] " Marcelo Diop-Gonzalez
2019-11-20 15:36 ` [PATCH 1/3] staging: vchiq_dump: Replace min with min_t Marcelo Diop-Gonzalez
2019-11-20 15:46   ` Greg KH
2019-11-20 15:36 ` [PATCH 2/3] staging: vchiq: Refactor indentation in vchiq_dump_* functions Marcelo Diop-Gonzalez
2019-11-20 15:36 ` [PATCH 3/3] staging: vchiq: Have vchiq_dump_* functions return an error code Marcelo Diop-Gonzalez
2019-11-20 18:50   ` Dan Carpenter
2019-11-21 21:25     ` Marcelo Diop-Gonzalez
2019-11-20 20:20 ` Marcelo Diop-Gonzalez [this message]
2019-11-20 20:20   ` [PATCH v2 1/4] staging: vchiq: Fix block comment format in vchiq_dump() Marcelo Diop-Gonzalez
2019-11-20 20:21   ` [PATCH v2 2/4] staging: vchiq_dump: Replace min with min_t Marcelo Diop-Gonzalez
2019-11-20 20:21   ` [PATCH v2 3/4] staging: vchiq: Refactor indentation in vchiq_dump_* functions Marcelo Diop-Gonzalez
2019-11-20 20:21   ` [PATCH v2 4/4] staging: vchiq: Have vchiq_dump_* functions return an error code Marcelo Diop-Gonzalez
2019-11-21 19:38   ` [PATCH v2 0/4] staging: vchiq: Fix vchiq_read return value in case of error Nicolas Saenz Julienne
2019-11-21 21:24     ` Marcelo Diop-Gonzalez
2019-11-21 10:42 ` [PATCH 0/3] " Stefan Wahren
2019-11-21 19:41   ` Nicolas Saenz Julienne

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