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>

1 files changed, 13 insertions, 17 deletions

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++)
         {