If reg_r() fails, then gspca_dev->usb_buf was left uninitialized,
and some drivers used the contents of that buffer in logic.

This caused several syzbot errors:

https://syzkaller.appspot.com/bug?extid=397fd082ce5143e2f67d
https://syzkaller.appspot.com/bug?extid=1a35278dd0ebfb3a038a
https://syzkaller.appspot.com/bug?extid=06ddf1788cfd048c5e82

I analyzed the gspca drivers and zeroed the buffer where needed.

Signed-off-by: Hans Verkuil <hverkuil-ci...@xs4all.nl>
Reported-and-tested-by: syzbot+1a35278dd0ebfb3a0...@syzkaller.appspotmail.com
Reported-and-tested-by: syzbot+397fd082ce5143e2f...@syzkaller.appspotmail.com
Reported-and-tested-by: syzbot+06ddf1788cfd048c5...@syzkaller.appspotmail.com
---
Changes in v2: use USB_BUF_SZ instead of sizeof(gspca_dev->usb_buf) since
usb_buf is a pointer.
---
diff --git a/drivers/media/usb/gspca/konica.c b/drivers/media/usb/gspca/konica.c
index d8e40137a204..53db9a2895ea 100644
--- a/drivers/media/usb/gspca/konica.c
+++ b/drivers/media/usb/gspca/konica.c
@@ -114,6 +114,11 @@ static void reg_r(struct gspca_dev *gspca_dev, u16 value, 
u16 index)
        if (ret < 0) {
                pr_err("reg_r err %d\n", ret);
                gspca_dev->usb_err = ret;
+               /*
+                * Make sure the buffer is zeroed to avoid uninitialized
+                * values.
+                */
+               memset(gspca_dev->usb_buf, 0, 2);
        }
 }

diff --git a/drivers/media/usb/gspca/nw80x.c b/drivers/media/usb/gspca/nw80x.c
index 59649704beba..db3e1657670b 100644
--- a/drivers/media/usb/gspca/nw80x.c
+++ b/drivers/media/usb/gspca/nw80x.c
@@ -1572,6 +1572,11 @@ static void reg_r(struct gspca_dev *gspca_dev,
        if (ret < 0) {
                pr_err("reg_r err %d\n", ret);
                gspca_dev->usb_err = ret;
+               /*
+                * Make sure the buffer is zeroed to avoid uninitialized
+                * values.
+                */
+               memset(gspca_dev->usb_buf, 0, USB_BUF_SZ);
                return;
        }
        if (len == 1)
diff --git a/drivers/media/usb/gspca/ov519.c b/drivers/media/usb/gspca/ov519.c
index cfb1f53bc17e..f417dfc0b872 100644
--- a/drivers/media/usb/gspca/ov519.c
+++ b/drivers/media/usb/gspca/ov519.c
@@ -2073,6 +2073,11 @@ static int reg_r(struct sd *sd, u16 index)
        } else {
                gspca_err(gspca_dev, "reg_r %02x failed %d\n", index, ret);
                sd->gspca_dev.usb_err = ret;
+               /*
+                * Make sure the result is zeroed to avoid uninitialized
+                * values.
+                */
+               gspca_dev->usb_buf[0] = 0;
        }

        return ret;
@@ -2101,6 +2106,11 @@ static int reg_r8(struct sd *sd,
        } else {
                gspca_err(gspca_dev, "reg_r8 %02x failed %d\n", index, ret);
                sd->gspca_dev.usb_err = ret;
+               /*
+                * Make sure the buffer is zeroed to avoid uninitialized
+                * values.
+                */
+               memset(gspca_dev->usb_buf, 0, 8);
        }

        return ret;
diff --git a/drivers/media/usb/gspca/ov534.c b/drivers/media/usb/gspca/ov534.c
index 56521c991db4..185c1f10fb30 100644
--- a/drivers/media/usb/gspca/ov534.c
+++ b/drivers/media/usb/gspca/ov534.c
@@ -693,6 +693,11 @@ static u8 ov534_reg_read(struct gspca_dev *gspca_dev, u16 
reg)
        if (ret < 0) {
                pr_err("read failed %d\n", ret);
                gspca_dev->usb_err = ret;
+               /*
+                * Make sure the result is zeroed to avoid uninitialized
+                * values.
+                */
+               gspca_dev->usb_buf[0] = 0;
        }
        return gspca_dev->usb_buf[0];
 }
diff --git a/drivers/media/usb/gspca/ov534_9.c 
b/drivers/media/usb/gspca/ov534_9.c
index 867f860a9650..91efc650cf76 100644
--- a/drivers/media/usb/gspca/ov534_9.c
+++ b/drivers/media/usb/gspca/ov534_9.c
@@ -1145,6 +1145,7 @@ static u8 reg_r(struct gspca_dev *gspca_dev, u16 reg)
        if (ret < 0) {
                pr_err("reg_r err %d\n", ret);
                gspca_dev->usb_err = ret;
+               return 0;
        }
        return gspca_dev->usb_buf[0];
 }
diff --git a/drivers/media/usb/gspca/se401.c b/drivers/media/usb/gspca/se401.c
index 061deee138c3..e087cfb5980b 100644
--- a/drivers/media/usb/gspca/se401.c
+++ b/drivers/media/usb/gspca/se401.c
@@ -101,6 +101,11 @@ static void se401_read_req(struct gspca_dev *gspca_dev, 
u16 req, int silent)
                        pr_err("read req failed req %#04x error %d\n",
                               req, err);
                gspca_dev->usb_err = err;
+               /*
+                * Make sure the buffer is zeroed to avoid uninitialized
+                * values.
+                */
+               memset(gspca_dev->usb_buf, 0, READ_REQ_SIZE);
        }
 }

diff --git a/drivers/media/usb/gspca/sn9c20x.c 
b/drivers/media/usb/gspca/sn9c20x.c
index b43f89fee6c1..490af88e88ac 100644
--- a/drivers/media/usb/gspca/sn9c20x.c
+++ b/drivers/media/usb/gspca/sn9c20x.c
@@ -909,6 +909,11 @@ static void reg_r(struct gspca_dev *gspca_dev, u16 reg, 
u16 length)
        if (unlikely(result < 0 || result != length)) {
                pr_err("Read register %02x failed %d\n", reg, result);
                gspca_dev->usb_err = result;
+               /*
+                * Make sure the buffer is zeroed to avoid uninitialized
+                * values.
+                */
+               memset(gspca_dev->usb_buf, 0, USB_BUF_SZ);
        }
 }

diff --git a/drivers/media/usb/gspca/sonixb.c b/drivers/media/usb/gspca/sonixb.c
index 046fc2c2a135..4d655e2da9cb 100644
--- a/drivers/media/usb/gspca/sonixb.c
+++ b/drivers/media/usb/gspca/sonixb.c
@@ -453,6 +453,11 @@ static void reg_r(struct gspca_dev *gspca_dev,
                dev_err(gspca_dev->v4l2_dev.dev,
                        "Error reading register %02x: %d\n", value, res);
                gspca_dev->usb_err = res;
+               /*
+                * Make sure the result is zeroed to avoid uninitialized
+                * values.
+                */
+               gspca_dev->usb_buf[0] = 0;
        }
 }

diff --git a/drivers/media/usb/gspca/sonixj.c b/drivers/media/usb/gspca/sonixj.c
index 50a6c8425827..acf931a2bf1f 100644
--- a/drivers/media/usb/gspca/sonixj.c
+++ b/drivers/media/usb/gspca/sonixj.c
@@ -1162,6 +1162,11 @@ static void reg_r(struct gspca_dev *gspca_dev,
        if (ret < 0) {
                pr_err("reg_r err %d\n", ret);
                gspca_dev->usb_err = ret;
+               /*
+                * Make sure the buffer is zeroed to avoid uninitialized
+                * values.
+                */
+               memset(gspca_dev->usb_buf, 0, USB_BUF_SZ);
        }
 }

diff --git a/drivers/media/usb/gspca/spca1528.c 
b/drivers/media/usb/gspca/spca1528.c
index 2ae03b60163f..ec1811895f85 100644
--- a/drivers/media/usb/gspca/spca1528.c
+++ b/drivers/media/usb/gspca/spca1528.c
@@ -71,6 +71,11 @@ static void reg_r(struct gspca_dev *gspca_dev,
        if (ret < 0) {
                pr_err("reg_r err %d\n", ret);
                gspca_dev->usb_err = ret;
+               /*
+                * Make sure the buffer is zeroed to avoid uninitialized
+                * values.
+                */
+               memset(gspca_dev->usb_buf, 0, USB_BUF_SZ);
        }
 }

diff --git a/drivers/media/usb/gspca/sq930x.c b/drivers/media/usb/gspca/sq930x.c
index d1ba0888d798..cd9bf31ed437 100644
--- a/drivers/media/usb/gspca/sq930x.c
+++ b/drivers/media/usb/gspca/sq930x.c
@@ -425,6 +425,11 @@ static void reg_r(struct gspca_dev *gspca_dev,
        if (ret < 0) {
                pr_err("reg_r %04x failed %d\n", value, ret);
                gspca_dev->usb_err = ret;
+               /*
+                * Make sure the buffer is zeroed to avoid uninitialized
+                * values.
+                */
+               memset(gspca_dev->usb_buf, 0, USB_BUF_SZ);
        }
 }

diff --git a/drivers/media/usb/gspca/sunplus.c 
b/drivers/media/usb/gspca/sunplus.c
index d0ddfa957ca9..0648d0db5515 100644
--- a/drivers/media/usb/gspca/sunplus.c
+++ b/drivers/media/usb/gspca/sunplus.c
@@ -255,6 +255,11 @@ static void reg_r(struct gspca_dev *gspca_dev,
        if (ret < 0) {
                pr_err("reg_r err %d\n", ret);
                gspca_dev->usb_err = ret;
+               /*
+                * Make sure the buffer is zeroed to avoid uninitialized
+                * values.
+                */
+               memset(gspca_dev->usb_buf, 0, USB_BUF_SZ);
        }
 }

diff --git a/drivers/media/usb/gspca/vc032x.c b/drivers/media/usb/gspca/vc032x.c
index 588a847ea483..e652a6becb3e 100644
--- a/drivers/media/usb/gspca/vc032x.c
+++ b/drivers/media/usb/gspca/vc032x.c
@@ -2906,6 +2906,11 @@ static void reg_r_i(struct gspca_dev *gspca_dev,
        if (ret < 0) {
                pr_err("reg_r err %d\n", ret);
                gspca_dev->usb_err = ret;
+               /*
+                * Make sure the buffer is zeroed to avoid uninitialized
+                * values.
+                */
+               memset(gspca_dev->usb_buf, 0, USB_BUF_SZ);
        }
 }
 static void reg_r(struct gspca_dev *gspca_dev,
diff --git a/drivers/media/usb/gspca/w996Xcf.c 
b/drivers/media/usb/gspca/w996Xcf.c
index 16b679c2de21..a8350ee9712f 100644
--- a/drivers/media/usb/gspca/w996Xcf.c
+++ b/drivers/media/usb/gspca/w996Xcf.c
@@ -133,6 +133,11 @@ static int w9968cf_read_sb(struct sd *sd)
        } else {
                pr_err("Read SB reg [01] failed\n");
                sd->gspca_dev.usb_err = ret;
+               /*
+                * Make sure the buffer is zeroed to avoid uninitialized
+                * values.
+                */
+               memset(sd->gspca_dev.usb_buf, 0, 2);
        }

        udelay(W9968CF_I2C_BUS_DELAY);

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