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, 2 insertions, 6 deletions

diff --git a/sound/oss/opl3.c b/sound/oss/opl3.c
index 938c48c4358..cbf957424d5 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)