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++)
 	{