Was: [PATCH] sound/oss/midi_synth: prevent underflow, use of
uninitialized value, and signedness issue
The offset passed to midi_synth_load_patch() can be essentially
arbitrary. If it's greater than the header length, this will result in
a copy_from_user(dst, src, negative_val). While this will just return
-EFAULT on x86, on other architectures this may cause memory corruption.
Additionally, the length field of the sysex_info structure may not be
initialized prior to its use. Finally, a signed comparison may result
in an unintentionally large loop.
On suggestion by Takashi Iwai, version two removes the offset argument
from the load_patch callbacks entirely, which also resolves similar
issues in opl3. Compile tested only.
Signed-off-by: Dan Rosenberg <[email protected]>
Cc: [email protected]
---
sound/oss/dev_table.h | 2 +-
sound/oss/midi_synth.c | 27 ++++++++++++---------------
sound/oss/midi_synth.h | 2 +-
sound/oss/opl3.c | 4 ++--
sound/oss/sequencer.c | 2 +-
5 files changed, 17 insertions(+), 20 deletions(-)
diff --git a/sound/oss/dev_table.h b/sound/oss/dev_table.h
index b7617be..0199a31 100644
--- a/sound/oss/dev_table.h
+++ b/sound/oss/dev_table.h
@@ -271,7 +271,7 @@ struct synth_operations
void (*reset) (int dev);
void (*hw_control) (int dev, unsigned char *event);
int (*load_patch) (int dev, int format, const char __user *addr,
- int offs, int count, int pmgr_flag);
+ int count, int pmgr_flag);
void (*aftertouch) (int dev, int voice, int pressure);
void (*controller) (int dev, int voice, int ctrl_num, int value);
void (*panning) (int dev, int voice, int value);
diff --git a/sound/oss/midi_synth.c b/sound/oss/midi_synth.c
index 3c09374..8d3611c 100644
--- a/sound/oss/midi_synth.c
+++ b/sound/oss/midi_synth.c
@@ -476,7 +476,7 @@ EXPORT_SYMBOL(midi_synth_hw_control);
int
midi_synth_load_patch(int dev, int format, const char __user *addr,
- int offs, int count, int pmgr_flag)
+ int count, int pmgr_flag)
{
int orig_dev = synth_devs[dev]->midi_dev;
@@ -491,16 +491,14 @@ midi_synth_load_patch(int dev, int format, const char __user *addr,
if (!prefix_cmd(orig_dev, 0xf0))
return 0;
+ /* Invalid patch format */
if (format != SYSEX_PATCH)
- {
-/* printk("MIDI Error: Invalid patch format (key) 0x%x\n", format);*/
return -EINVAL;
- }
+
+ /* Patch header too short */
if (count < hdr_size)
- {
-/* printk("MIDI Error: Patch header too short\n");*/
return -EINVAL;
- }
+
count -= hdr_size;
/*
@@ -508,16 +506,15 @@ midi_synth_load_patch(int dev, int format, const char __user *addr,
* been transferred already.
*/
- if(copy_from_user(&((char *) &sysex)[offs], &(addr)[offs], hdr_size - offs))
+ if (copy_from_user(&sysex, addr, hdr_size))
return -EFAULT;
-
- if (count < sysex.len)
- {
-/* printk(KERN_WARNING "MIDI Warning: Sysex record too short (%d<%d)\n", count, (int) sysex.len);*/
+
+ /* Sysex record too short */
+ if ((unsigned)count < (unsigned)sysex.len)
sysex.len = count;
- }
- left = sysex.len;
- src_offs = 0;
+
+ left = sysex.len;
+ src_offs = 0;
for (i = 0; i < left && !signal_pending(current); i++)
{
diff --git a/sound/oss/midi_synth.h b/sound/oss/midi_synth.h
index 6bc9d00..b64ddd6 100644
--- a/sound/oss/midi_synth.h
+++ b/sound/oss/midi_synth.h
@@ -8,7 +8,7 @@ int midi_synth_open (int dev, int mode);
void midi_synth_close (int dev);
void midi_synth_hw_control (int dev, unsigned char *event);
int midi_synth_load_patch (int dev, int format, const char __user * addr,
- int offs, int count, int pmgr_flag);
+ int count, int pmgr_flag);
void midi_synth_panning (int dev, int channel, int pressure);
void midi_synth_aftertouch (int dev, int channel, int pressure);
void midi_synth_controller (int dev, int channel, int ctrl_num, int value);
diff --git a/sound/oss/opl3.c b/sound/oss/opl3.c
index 938c48c..a3bec38 100644
--- a/sound/oss/opl3.c
+++ b/sound/oss/opl3.c
@@ -820,7 +820,7 @@ static void opl3_hw_control(int dev, unsigned char *event)
}
static int opl3_load_patch(int dev, int format, const char __user *addr,
- int offs, int count, int pmgr_flag)
+ int count, int pmgr_flag)
{
struct sbi_instrument ins;
@@ -834,7 +834,7 @@ static int opl3_load_patch(int dev, int format, const char __user *addr,
* What the fuck is going on here? We leave junk in the beginning
* of ins and then check the field pretty close to that beginning?
*/
- if(copy_from_user(&((char *) &ins)[offs], addr + offs, sizeof(ins) - offs))
+ if (copy_from_user(&ins, addr, sizeof(ins)))
return -EFAULT;
if (ins.channel < 0 || ins.channel >= SBFM_MAXINSTR)
diff --git a/sound/oss/sequencer.c b/sound/oss/sequencer.c
index 5ea1098..2e842cb 100644
--- a/sound/oss/sequencer.c
+++ b/sound/oss/sequencer.c
@@ -241,7 +241,7 @@ int sequencer_write(int dev, struct file *file, const char __user *buf, int coun
return -ENXIO;
fmt = (*(short *) &event_rec[0]) & 0xffff;
- err = synth_devs[dev]->load_patch(dev, fmt, buf, p + 4, c, 0);
+ err = synth_devs[dev]->load_patch(dev, fmt, buf, c, 0);
if (err < 0)
return err;
At Wed, 23 Mar 2011 09:47:22 -0400,
Dan Rosenberg wrote:
> --- a/sound/oss/midi_synth.c
> +++ b/sound/oss/midi_synth.c
> @@ -508,16 +506,15 @@ midi_synth_load_patch(int dev, int format, const char __user *addr,
> * been transferred already.
> */
>
> - if(copy_from_user(&((char *) &sysex)[offs], &(addr)[offs], hdr_size - offs))
> + if (copy_from_user(&sysex, addr, hdr_size))
Please correct the comment in the above as well.
With this change, the transfer is no longer partial.
> --- a/sound/oss/opl3.c
> +++ b/sound/oss/opl3.c
...
> @@ -834,7 +834,7 @@ static int opl3_load_patch(int dev, int format, const char __user *addr,
> * What the fuck is going on here? We leave junk in the beginning
> * of ins and then check the field pretty close to that beginning?
> */
> - if(copy_from_user(&((char *) &ins)[offs], addr + offs, sizeof(ins) - offs))
> + if (copy_from_user(&ins, addr, sizeof(ins)))
Ditto.
> return -EFAULT;
>
> if (ins.channel < 0 || ins.channel >= SBFM_MAXINSTR)
> diff --git a/sound/oss/sequencer.c b/sound/oss/sequencer.c
> index 5ea1098..2e842cb 100644
> --- a/sound/oss/sequencer.c
> +++ b/sound/oss/sequencer.c
> @@ -241,7 +241,7 @@ int sequencer_write(int dev, struct file *file, const char __user *buf, int coun
> return -ENXIO;
>
> fmt = (*(short *) &event_rec[0]) & 0xffff;
> - err = synth_devs[dev]->load_patch(dev, fmt, buf, p + 4, c, 0);
> + err = synth_devs[dev]->load_patch(dev, fmt, buf, c, 0);
The address must be "buf + p + 4" instead of "buf", when you omit the
offset argument.
thanks,
Takashi
On Wed, 2011-03-23 at 14:59 +0100, Takashi Iwai wrote:
> At Wed, 23 Mar 2011 09:47:22 -0400,
> Dan Rosenberg wrote:
> > --- a/sound/oss/midi_synth.c
> > +++ b/sound/oss/midi_synth.c
> > @@ -508,16 +506,15 @@ midi_synth_load_patch(int dev, int format, const char __user *addr,
> > * been transferred already.
> > */
> >
> > - if(copy_from_user(&((char *) &sysex)[offs], &(addr)[offs], hdr_size - offs))
> > + if (copy_from_user(&sysex, addr, hdr_size))
>
> Please correct the comment in the above as well.
> With this change, the transfer is no longer partial.
Will do.
>
> > --- a/sound/oss/opl3.c
> > +++ b/sound/oss/opl3.c
> ...
> > @@ -834,7 +834,7 @@ static int opl3_load_patch(int dev, int format, const char __user *addr,
> > * What the fuck is going on here? We leave junk in the beginning
> > * of ins and then check the field pretty close to that beginning?
> > */
> > - if(copy_from_user(&((char *) &ins)[offs], addr + offs, sizeof(ins) - offs))
> > + if (copy_from_user(&ins, addr, sizeof(ins)))
>
> Ditto.
Likewise.
>
> > return -EFAULT;
> >
> > if (ins.channel < 0 || ins.channel >= SBFM_MAXINSTR)
> > diff --git a/sound/oss/sequencer.c b/sound/oss/sequencer.c
> > index 5ea1098..2e842cb 100644
> > --- a/sound/oss/sequencer.c
> > +++ b/sound/oss/sequencer.c
> > @@ -241,7 +241,7 @@ int sequencer_write(int dev, struct file *file, const char __user *buf, int coun
> > return -ENXIO;
> >
> > fmt = (*(short *) &event_rec[0]) & 0xffff;
> > - err = synth_devs[dev]->load_patch(dev, fmt, buf, p + 4, c, 0);
> > + err = synth_devs[dev]->load_patch(dev, fmt, buf, c, 0);
>
> The address must be "buf + p + 4" instead of "buf", when you omit the
> offset argument.
>
Are you sure? Previously, the copy of the header was from (buf + p + 4)
to (dst + p + 4) with length (hdr_size - (p + 4)), and now the copy is
from buf to dst with length hdr_size. If I do as you suggest, then the
copy will be from (buf + p + 4) to dst for the header.
-Dan
>
> thanks,
>
> Takashi
At Wed, 23 Mar 2011 10:06:22 -0400,
Dan Rosenberg wrote:
>
> On Wed, 2011-03-23 at 14:59 +0100, Takashi Iwai wrote:
> > At Wed, 23 Mar 2011 09:47:22 -0400,
> > Dan Rosenberg wrote:
> > > --- a/sound/oss/midi_synth.c
> > > +++ b/sound/oss/midi_synth.c
> > > @@ -508,16 +506,15 @@ midi_synth_load_patch(int dev, int format, const char __user *addr,
> > > * been transferred already.
> > > */
> > >
> > > - if(copy_from_user(&((char *) &sysex)[offs], &(addr)[offs], hdr_size - offs))
> > > + if (copy_from_user(&sysex, addr, hdr_size))
> >
> > Please correct the comment in the above as well.
> > With this change, the transfer is no longer partial.
>
> Will do.
>
> >
> > > --- a/sound/oss/opl3.c
> > > +++ b/sound/oss/opl3.c
> > ...
> > > @@ -834,7 +834,7 @@ static int opl3_load_patch(int dev, int format, const char __user *addr,
> > > * What the fuck is going on here? We leave junk in the beginning
> > > * of ins and then check the field pretty close to that beginning?
> > > */
> > > - if(copy_from_user(&((char *) &ins)[offs], addr + offs, sizeof(ins) - offs))
> > > + if (copy_from_user(&ins, addr, sizeof(ins)))
> >
> > Ditto.
>
> Likewise.
>
> >
> > > return -EFAULT;
> > >
> > > if (ins.channel < 0 || ins.channel >= SBFM_MAXINSTR)
> > > diff --git a/sound/oss/sequencer.c b/sound/oss/sequencer.c
> > > index 5ea1098..2e842cb 100644
> > > --- a/sound/oss/sequencer.c
> > > +++ b/sound/oss/sequencer.c
> > > @@ -241,7 +241,7 @@ int sequencer_write(int dev, struct file *file, const char __user *buf, int coun
> > > return -ENXIO;
> > >
> > > fmt = (*(short *) &event_rec[0]) & 0xffff;
> > > - err = synth_devs[dev]->load_patch(dev, fmt, buf, p + 4, c, 0);
> > > + err = synth_devs[dev]->load_patch(dev, fmt, buf, c, 0);
> >
> > The address must be "buf + p + 4" instead of "buf", when you omit the
> > offset argument.
> >
>
> Are you sure? Previously, the copy of the header was from (buf + p + 4)
> to (dst + p + 4) with length (hdr_size - (p + 4)), and now the copy is
> from buf to dst with length hdr_size. If I do as you suggest, then the
> copy will be from (buf + p + 4) to dst for the header.
Hm, looking back to the original code, I found that I almost forgot
the trickiness of patch-loading in OSS. Actually, it should be like:
err = synth_devs[dev]->load_patch(dev, fmt, buf + p, c, 0);
Here, "buf + p" points to the 4-byte event packet that is being
processed. And, these 4 bytes are also shared with the first 4 bytes
of struct sysex_info or struct sbi_instrument. That is,
sysex_info.key == fmt and sysex_info.device_no == dev.
The problem in the original code is that it tries to avoid extra
copying of these 4 bytes, but failed to handle correctly, by
misinterpreting offs parameter.
thanks,
Takashi