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Subject[PATCH] sound/oss/midi_synth: prevent underflow, use of uninitialized value, and signedness issue
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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.

This patch fixes all these issues, as well as some cleanup to prevent
checkpatch.pl from complaining.

Signed-off-by: Dan Rosenberg <drosenberg@vsecurity.com>
Cc: stable@kernel.org
---
sound/oss/midi_synth.c | 27 ++++++++++++++-------------
1 files changed, 14 insertions(+), 13 deletions(-)
diff --git a/sound/oss/midi_synth.c b/sound/oss/midi_synth.c
index 3c09374..3500f80 100644
--- a/sound/oss/midi_synth.c
+++ b/sound/oss/midi_synth.c
@@ -491,16 +491,18 @@ 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;
- }
+
+ /* Offset too high */
+ if (offs > offsetof(struct sysex_info, len) || offs < 0)
+ return -EINVAL;
+
count -= hdr_size;

/*
@@ -510,14 +512,13 @@ midi_synth_load_patch(int dev, int format, const char __user *addr,

if(copy_from_user(&((char *) &sysex)[offs], &(addr)[offs], hdr_size - offs))
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++)
{



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