[syzbot] [media?] KMSAN: uninit-value in cxusb_i2c_xfer

Hello,

syzbot found the following issue on:

HEAD commit: 4e82c87058f4 Merge tag 'rust-6.15' of git://git.kernel.org..
git tree: upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=166a7bcf980000
kernel config: https://syzkaller.appspot.com/x/.config?x=378acbc45ac948ee
dashboard link: https://syzkaller.appspot.com/bug?extid=526bd95c0ec629993bf3
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13488fb0580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1595dc74580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/6045aa9da8ac/disk-4e82c870.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1adf8802c9fe/vmlinux-4e82c870.xz
kernel image: https://storage.googleapis.com/syzbot-assets/9eb6c71670e3/bzImage-4e82c870.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email protected]

dvb-usb: bulk message failed: -22 (3/0)
=====================================================
BUG: KMSAN: uninit-value in cxusb_gpio_tuner drivers/media/usb/dvb-usb/cxusb.c:124 [inline]
BUG: KMSAN: uninit-value in cxusb_i2c_xfer+0x153a/0x1a60 drivers/media/usb/dvb-usb/cxusb.c:196
cxusb_gpio_tuner drivers/media/usb/dvb-usb/cxusb.c:124 [inline]
cxusb_i2c_xfer+0x153a/0x1a60 drivers/media/usb/dvb-usb/cxusb.c:196
__i2c_transfer+0xe25/0x3150 drivers/i2c/i2c-core-base.c:-1
i2c_transfer+0x317/0x4a0 drivers/i2c/i2c-core-base.c:2315
i2c_transfer_buffer_flags+0x125/0x1e0 drivers/i2c/i2c-core-base.c:2343
i2c_master_send include/linux/i2c.h:109 [inline]
i2cdev_write+0x210/0x280 drivers/i2c/i2c-dev.c:183
do_loop_readv_writev fs/read_write.c:848 [inline]
vfs_writev+0x963/0x14e0 fs/read_write.c:1057
do_writev+0x247/0x5c0 fs/read_write.c:1101
__do_sys_writev fs/read_write.c:1169 [inline]
__se_sys_writev fs/read_write.c:1166 [inline]
__x64_sys_writev+0x98/0xe0 fs/read_write.c:1166
x64_sys_call+0x2229/0x3c80 arch/x86/include/generated/asm/syscalls_64.h:21
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xcd/0x1e0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Local variable i.i809 created at:
cxusb_gpio_tuner drivers/media/usb/dvb-usb/cxusb.c:116 [inline]
cxusb_i2c_xfer+0x323/0x1a60 drivers/media/usb/dvb-usb/cxusb.c:196
__i2c_transfer+0xe25/0x3150 drivers/i2c/i2c-core-base.c:-1

CPU: 0 UID: 0 PID: 5806 Comm: syz-executor225 Not tainted 6.14.0-syzkaller-10892-g4e82c87058f4 #0 PREEMPT(undef)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
=====================================================


---
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diff --git a/drivers/media/usb/dvb-usb/cxusb.c b/drivers/media/usb/dvb-usb/cxusb.c
index f44529b40989..d0501c1e81d6 100644
--- a/drivers/media/usb/dvb-usb/cxusb.c
+++ b/drivers/media/usb/dvb-usb/cxusb.c
@@ -119,9 +119,8 @@ static void cxusb_gpio_tuner(struct dvb_usb_device *d, int onoff)

o[0] = GPIO_TUNER;
o[1] = onoff;
- cxusb_ctrl_msg(d, CMD_GPIO_WRITE, o, 2, &i, 1);

- if (i != 0x01)
+ if (!cxusb_ctrl_msg(d, CMD_GPIO_WRITE, o, 2, &i, 1) && i != 0x01)
dev_info(&d->udev->dev, "gpio_write failed.\n");

st->gpio_write_state[GPIO_TUNER] = onoff;
--
2.43.0

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: [email protected]
Tested-by: [email protected]

Tested on:

commit: a8662bcd Merge tag 'v6.15-p3' of git://git.kernel.org/..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14d64be4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=47d69504cb18f07a
patch: https://syzkaller.appspot.com/x/patch.diff?x=1300efb0580000

Note: testing is done by a robot and is best-effort only.

syzbot reported a uninit-value in cxusb_i2c_xfer. [1]

Only when the write operation of usb_bulk_msg() in dvb_usb_generic_rw()
succeeds and rlen is greater than 0, the read operation of usb_bulk_msg()
will be executed to read rlen bytes of data from the dvb device into the
rbuf.

In this case, although rlen is 1, the write operation failed which resulted
in the dvb read operation not being executed, and ultimately variable i was
not initialized.

[1]
Reported-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=526bd95c0ec629993bf3
Tested-by: [email protected]
Signed-off-by: Edward Adam Davis <[email protected]>
---
drivers/media/usb/dvb-usb/cxusb.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)