| Message ID | 20210325212202.142945-1-alaaemadhossney.ae@gmail.com |
|---|---|
| State | New |
| Headers | show |
| Series | media: sq905.c: fix uninitialized variable | expand |
On Thu, Mar 25, 2021 at 11:22:02PM +0200, Alaa Emad wrote: > Reported-by: syzbot+a4e309017a5f3a24c7b3@syzkaller.appspotmail.com > Signed-off-by: Alaa Emad <alaaemadhossney.ae@gmail.com> > --- I know I do not take patches with no changelog text, but other maintainers might be more leniant :( thanks, greg k-h
On Fri, Mar 26, 2021 at 8:11 AM Greg KH <gregkh@linuxfoundation.org> wrote: > > On Thu, Mar 25, 2021 at 11:22:02PM +0200, Alaa Emad wrote: > > Reported-by: syzbot+a4e309017a5f3a24c7b3@syzkaller.appspotmail.com > > Signed-off-by: Alaa Emad <alaaemadhossney.ae@gmail.com> > > --- > > I know I do not take patches with no changelog text, but other > maintainers might be more leniant :( I wonder if it's the right fix or not. Initializing variables will, of course, silence the warning, but it's not necessarily the right fix. I suspect there is something wrong in how ret/act_len are user/checked.
Hi! On Fri, 2021-03-26 at 08:14 +0100, 'Dmitry Vyukov' via syzkaller wrote: > On Fri, Mar 26, 2021 at 8:11 AM Greg KH <gregkh@linuxfoundation.org> > wrote: > > > > On Thu, Mar 25, 2021 at 11:22:02PM +0200, Alaa Emad wrote: > > > Reported-by: syzbot+a4e309017a5f3a24c7b3@syzkaller.appspotmail.com > > > Signed-off-by: Alaa Emad <alaaemadhossney.ae@gmail.com> > > > --- > > > > I know I do not take patches with no changelog text, but other > > maintainers might be more leniant :( > > I wonder if it's the right fix or not. > Initializing variables will, of course, silence the warning, but it's > not necessarily the right fix. I suspect there is something wrong in > how ret/act_len are user/checked. > There is a problem in usb_bulk_msg() call. It could return before act_len initialization, so i think, act_len should be intialized with smth wrong like 0 or -1. BTW, I already send patch for that, but it was marked as obsoleted. -- With regards, Pavel Skripkin
On Fri, Mar 26, 2021 at 8:24 AM Pavel Skripkin <paskripkin@gmail.com> wrote: > > Hi! > > On Fri, 2021-03-26 at 08:14 +0100, 'Dmitry Vyukov' via syzkaller wrote: > > On Fri, Mar 26, 2021 at 8:11 AM Greg KH <gregkh@linuxfoundation.org> > > wrote: > > > > > > On Thu, Mar 25, 2021 at 11:22:02PM +0200, Alaa Emad wrote: > > > > Reported-by: syzbot+a4e309017a5f3a24c7b3@syzkaller.appspotmail.com > > > > Signed-off-by: Alaa Emad <alaaemadhossney.ae@gmail.com> > > > > --- > > > > > > I know I do not take patches with no changelog text, but other > > > maintainers might be more leniant :( > > > > I wonder if it's the right fix or not. > > Initializing variables will, of course, silence the warning, but it's > > not necessarily the right fix. I suspect there is something wrong in > > how ret/act_len are user/checked. > > > > There is a problem in usb_bulk_msg() call. It could return before > act_len initialization, so i think, act_len should be intialized with > smth wrong like 0 or -1. BTW, I already send patch for that, but it was > marked as obsoleted. If usb_bulk_msg returns before act_len initialization, it should signify that fact with an error code in return value or something, right? It does not initialize act_len only in case of errors, right? If so, sq905_read_data must check ret and don't use act_for any checks. But it does, and that's I think the bug. Or maybe usb_bulk_msg does not properly signify that it failed (and did not initialize act_len). Either way silencing the warning with pre-initializing act_len looks very fishy. For example, consider, in some contexts it's OK to transmit 0-length packets, I don't know if it's the case for usb_bulk_msg or not, but it does not affect the idea. Now, if we pre-initialize act_len to 0, we can falsely think that such 0-length transfer has succeeded (act_len == size), while it actually failed (I assume so since usb_bulk_msg left act_len unitialized).
Hi! On Fri, 2021-03-26 at 08:40 +0100, Dmitry Vyukov wrote: > On Fri, Mar 26, 2021 at 8:24 AM Pavel Skripkin <paskripkin@gmail.com> > wrote: > > > > Hi! > > > > On Fri, 2021-03-26 at 08:14 +0100, 'Dmitry Vyukov' via syzkaller > > wrote: > > > On Fri, Mar 26, 2021 at 8:11 AM Greg KH > > > <gregkh@linuxfoundation.org> > > > wrote: > > > > > > > > On Thu, Mar 25, 2021 at 11:22:02PM +0200, Alaa Emad wrote: > > > > > Reported-by: > > > > > syzbot+a4e309017a5f3a24c7b3@syzkaller.appspotmail.com > > > > > Signed-off-by: Alaa Emad <alaaemadhossney.ae@gmail.com> > > > > > --- > > > > > > > > I know I do not take patches with no changelog text, but other > > > > maintainers might be more leniant :( > > > > > > I wonder if it's the right fix or not. > > > Initializing variables will, of course, silence the warning, but > > > it's > > > not necessarily the right fix. I suspect there is something wrong > > > in > > > how ret/act_len are user/checked. > > > > > > > There is a problem in usb_bulk_msg() call. It could return before > > act_len initialization, so i think, act_len should be intialized with > > smth wrong like 0 or -1. BTW, I already send patch for that, but it > > was > > marked as obsoleted. > > If usb_bulk_msg returns before act_len initialization, it should > signify that fact with an error code in return value or something, > right? It does not initialize act_len only in case of errors, right? > If so, sq905_read_data must check ret and don't use act_for any > checks. But it does, and that's I think the bug. Or maybe usb_bulk_msg > does not properly signify that it failed (and did not initialize > act_len). Either way silencing the warning with pre-initializing > act_len looks very fishy. > For example, consider, in some contexts it's OK to transmit 0-length > packets, I don't know if it's the case for usb_bulk_msg or not, but it > does not affect the idea. Now, if we pre-initialize act_len to 0, we > can falsely think that such 0-length transfer has succeeded (act_len > == size), while it actually failed (I assume so since usb_bulk_msg > left act_len unitialized). You are absolutely rigth, and sq905_read_data doesn't use act_len for checks in case of usb_bulk_msg fail. But it uses it for error printing: if (ret < 0 || act_len != size) { pr_err("bulk read fail (%d) len %d/%d\n", ret, act_len, size); return -EIO; } So, value like -1 can be a flag for smth went wrong internally. Or maybe remove this error log and replace it with other, which will rely on error code, idk how it will be better -- With regards, Pavel Skripkin
On Fri, Mar 26, 2021 at 8:53 AM Pavel Skripkin <paskripkin@gmail.com> wrote: > > Hi! > > On Fri, 2021-03-26 at 08:40 +0100, Dmitry Vyukov wrote: > > On Fri, Mar 26, 2021 at 8:24 AM Pavel Skripkin <paskripkin@gmail.com> > > wrote: > > > > > > Hi! > > > > > > On Fri, 2021-03-26 at 08:14 +0100, 'Dmitry Vyukov' via syzkaller > > > wrote: > > > > On Fri, Mar 26, 2021 at 8:11 AM Greg KH > > > > <gregkh@linuxfoundation.org> > > > > wrote: > > > > > > > > > > On Thu, Mar 25, 2021 at 11:22:02PM +0200, Alaa Emad wrote: > > > > > > Reported-by: > > > > > > syzbot+a4e309017a5f3a24c7b3@syzkaller.appspotmail.com > > > > > > Signed-off-by: Alaa Emad <alaaemadhossney.ae@gmail.com> > > > > > > --- > > > > > > > > > > I know I do not take patches with no changelog text, but other > > > > > maintainers might be more leniant :( > > > > > > > > I wonder if it's the right fix or not. > > > > Initializing variables will, of course, silence the warning, but > > > > it's > > > > not necessarily the right fix. I suspect there is something wrong > > > > in > > > > how ret/act_len are user/checked. > > > > > > > > > > There is a problem in usb_bulk_msg() call. It could return before > > > act_len initialization, so i think, act_len should be intialized with > > > smth wrong like 0 or -1. BTW, I already send patch for that, but it > > > was > > > marked as obsoleted. > > > > If usb_bulk_msg returns before act_len initialization, it should > > signify that fact with an error code in return value or something, > > right? It does not initialize act_len only in case of errors, right? > > If so, sq905_read_data must check ret and don't use act_for any > > checks. But it does, and that's I think the bug. Or maybe usb_bulk_msg > > does not properly signify that it failed (and did not initialize > > act_len). Either way silencing the warning with pre-initializing > > act_len looks very fishy. > > For example, consider, in some contexts it's OK to transmit 0-length > > packets, I don't know if it's the case for usb_bulk_msg or not, but it > > does not affect the idea. Now, if we pre-initialize act_len to 0, we > > can falsely think that such 0-length transfer has succeeded (act_len > > == size), while it actually failed (I assume so since usb_bulk_msg > > left act_len unitialized). > > You are absolutely rigth, and sq905_read_data doesn't use act_len for > checks in case of usb_bulk_msg fail. But it uses it for error printing: > > if (ret < 0 || act_len != size) { > pr_err("bulk read fail (%d) len %d/%d\n", ret, > act_len, size); > return -EIO; > } > > So, value like -1 can be a flag for smth went wrong internally. Or > maybe remove this error log and replace it with other, which will rely > on error code, idk how it will be better Oh, you are right. I was thinking it's the "ret < 0 || act_len != size" check where we use uninit act_len, which would be much worse. We could preinitialize act_len to, say, -1. But future readers may be confused as to why we need to init it (as I was confused). So another option may be to handle it during printing as: pr_err("bulk read fail (%d) len %d/%d\n", ret, ret < 0 ? -1 : act_len, size); It makes the intentions very explicit for a future reader.
diff --git a/drivers/media/usb/gspca/sq905.c b/drivers/media/usb/gspca/sq905.c index 97799cfb832e..54b733002f5c 100644 --- a/drivers/media/usb/gspca/sq905.c +++ b/drivers/media/usb/gspca/sq905.c @@ -157,8 +157,8 @@ static int sq905_ack_frame(struct gspca_dev *gspca_dev) static int sq905_read_data(struct gspca_dev *gspca_dev, u8 *data, int size, int need_lock) { - int ret; - int act_len; + int ret = 0; + int act_len = 0; gspca_dev->usb_buf[0] = '\0'; if (need_lock)
Reported-by: syzbot+a4e309017a5f3a24c7b3@syzkaller.appspotmail.com Signed-off-by: Alaa Emad <alaaemadhossney.ae@gmail.com> --- drivers/media/usb/gspca/sq905.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)