sound/oss: remove offset from load_patch callbacks

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.

v3 adjusts comments and hopefully gets copy offsets right.

Signed-off-by: Dan Rosenberg <drosenberg@vsecurity.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

5 files changed, 18 insertions, 26 deletions

diff --git a/sound/oss/dev_table.h b/sound/oss/dev_table.h
index b7617bee6388..0199a317c5a9 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 3c09374ea5bf..2292c230d7e6 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;
 
@@ -491,33 +491,29 @@ 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;
 
         /*
-         * Copy the header from user space but ignore the first bytes which have
-         * been transferred already.
+         * Copy the header from user space
          */
 
-        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 6bc9d00bc77c..b64ddd6c4abc 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 938c48c43585..cbf957424d5c 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;
 
@@ -830,11 +830,7 @@ static int opl3_load_patch(int dev, int format, const char __user *addr,
                 return -EINVAL;
         }
 
-        /*
-         * 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 5ea1098ac427..30bcfe470f83 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 + p, c, 0);
                         if (err < 0)
                                 return err;