[PATCH] crypto: nx - validate 'ignore' before subtracting in decompress

[Aldo Ariel Panzardo <qwe.aldo@gmail.com>]

The decompress() function subtracts the header-supplied `ignore` value
(a u16 from the compressed stream) from `dlen` (the number of bytes
produced by the decompressor) without checking that ignore <= dlen.

If a caller decompresses a crafted buffer where `hdr->ignore` exceeds
the actual decompressed length, the subtraction wraps around to a
near-UINT_MAX value.  The subsequent memcpy() then copies gigabytes of
data past the destination buffer, causing an out-of-bounds kernel write.

Add a bounds check before the subtraction and return -EINVAL if the
value is inconsistent.

Cc: stable@vger.kernel.org
Signed-off-by: Aldo Ariel Panzardo <qwe.aldo@gmail.com>
---
 drivers/crypto/nx/nx-842.c | 3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/crypto/nx/nx-842.c
+++ b/drivers/crypto/nx/nx-842.c
@@ -421,6 +421,8 @@
 
 	slen -= spadding;
 
+	if (ignore > dlen)
+		return -EINVAL;
 	dlen -= ignore;
 	if (ignore)
 		pr_debug("ignoring last %x bytes\n", ignore);

-- 
2.43.0