[syzbot] [media?] KMSAN: uninit-value in pctv452e_i2c_msg

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 9b0d551bcc05 Merge tag 'pull-misc' of git://git.kernel.org..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14e89a7c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=50fb29d81ff5a3df
dashboard link: https://syzkaller.appspot.com/bug?extid=480edd2cadb85ddb4bbe
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/90b0fb888152/disk-9b0d551b.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1120c646f284/vmlinux-9b0d551b.xz
kernel image: https://storage.googleapis.com/syzbot-assets/df9bbfa8cbe6/bzImage-9b0d551b.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+480edd...@syzkaller.appspotmail.com

=====================================================
BUG: KMSAN: uninit-value in hex_string+0x681/0x740 lib/vsprintf.c:1220
hex_string+0x681/0x740 lib/vsprintf.c:1220
pointer+0x2c7/0x1bd0 lib/vsprintf.c:2520
vsnprintf+0xf8a/0x1bd0 lib/vsprintf.c:2930
vscnprintf+0x6d/0x120 lib/vsprintf.c:2991
printk_sprint+0x53/0x5c0 kernel/printk/printk.c:2189
vprintk_store+0xbb9/0x1530 kernel/printk/printk.c:2309
vprintk_emit+0x21a/0xb60 kernel/printk/printk.c:2399
vprintk_default+0x3f/0x50 kernel/printk/printk.c:2438
vprintk+0x36/0x50 kernel/printk/printk_safe.c:82
_printk+0x17e/0x1b0 kernel/printk/printk.c:2448
pctv452e_i2c_msg+0x82a/0x8f0 drivers/media/usb/dvb-usb/pctv452e.c:467
pctv452e_i2c_xfer+0x2e6/0x4c0 drivers/media/usb/dvb-usb/pctv452e.c:502
__i2c_transfer+0xecd/0x3110 drivers/i2c/i2c-core-base.c:-1
i2c_transfer+0x300/0x4b0 drivers/i2c/i2c-core-base.c:2317
i2c_transfer_buffer_flags+0x138/0x200 drivers/i2c/i2c-core-base.c:2345
i2c_master_recv include/linux/i2c.h:79 [inline]
i2cdev_read+0x1b2/0x3c0 drivers/i2c/i2c-dev.c:155
vfs_read+0x27c/0xf90 fs/read_write.c:570
ksys_pread64 fs/read_write.c:763 [inline]
__do_sys_pread64 fs/read_write.c:771 [inline]
__se_sys_pread64 fs/read_write.c:768 [inline]
__x64_sys_pread64+0x2ab/0x3b0 fs/read_write.c:768
x64_sys_call+0x3370/0x3e30 arch/x86/include/generated/asm/syscalls_64.h:18
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd9/0x210 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was created at:
slab_post_alloc_hook mm/slub.c:4953 [inline]
slab_alloc_node mm/slub.c:5245 [inline]
__kmalloc_cache_noprof+0x8f5/0x16b0 mm/slub.c:5719
kmalloc_noprof include/linux/slab.h:957 [inline]
pctv452e_i2c_msg+0x98/0x8f0 drivers/media/usb/dvb-usb/pctv452e.c:425
pctv452e_i2c_xfer+0x2e6/0x4c0 drivers/media/usb/dvb-usb/pctv452e.c:502
__i2c_transfer+0xecd/0x3110 drivers/i2c/i2c-core-base.c:-1
i2c_transfer+0x300/0x4b0 drivers/i2c/i2c-core-base.c:2317
i2c_transfer_buffer_flags+0x138/0x200 drivers/i2c/i2c-core-base.c:2345
i2c_master_recv include/linux/i2c.h:79 [inline]
i2cdev_read+0x1b2/0x3c0 drivers/i2c/i2c-dev.c:155
vfs_read+0x27c/0xf90 fs/read_write.c:570
ksys_pread64 fs/read_write.c:763 [inline]
__do_sys_pread64 fs/read_write.c:771 [inline]
__se_sys_pread64 fs/read_write.c:768 [inline]
__x64_sys_pread64+0x2ab/0x3b0 fs/read_write.c:768
x64_sys_call+0x3370/0x3e30 arch/x86/include/generated/asm/syscalls_64.h:18
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd9/0x210 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

CPU: 1 UID: 0 PID: 10013 Comm: syz.1.697 Not tainted syzkaller #0 PREEMPT(none)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
=====================================================


---
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[Edward Adam Davis]

syzbot reported a uninit-value in pctv452e_i2c_msg. [1]

When the snd_len or rcv_len check fails and jumps to failed, buf is
uninitialized, triggering the uninit-value issue.

Setting the err() output buf byte count to 0 before jumping to failed
before initializing buf and setting it to 7 after initializing buf avoids
this warning.

[1]

BUG: KMSAN: uninit-value in hex_string+0x681/0x740 lib/vsprintf.c:1220

pctv452e_i2c_msg+0x82a/0x8f0 drivers/media/usb/dvb-usb/pctv452e.c:467
pctv452e_i2c_xfer+0x2e6/0x4c0 drivers/media/usb/dvb-usb/pctv452e.c:502

Reported-by: syzbot+480edd...@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=480edd2cadb85ddb4bbe
Signed-off-by: Edward Adam Davis <ead...@qq.com>
---
drivers/media/usb/dvb-usb/pctv452e.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/media/usb/dvb-usb/pctv452e.c b/drivers/media/usb/dvb-usb/pctv452e.c
index 5094de9a312e..3b6e86a8e9ff 100644
--- a/drivers/media/usb/dvb-usb/pctv452e.c
+++ b/drivers/media/usb/dvb-usb/pctv452e.c
@@ -420,7 +420,7 @@ static int pctv452e_i2c_msg(struct dvb_usb_device *d, u8 addr,
struct pctv452e_state *state = d->priv;
u8 *buf;
u8 id;
- int ret;
+ int ret, plen = 0;

buf = kmalloc(64, GFP_KERNEL);
if (!buf)
@@ -432,6 +432,7 @@ static int pctv452e_i2c_msg(struct dvb_usb_device *d, u8 addr,
if (snd_len > 64 - 7 || rcv_len > 64 - 7)
goto failed;

+ plen = 7;
buf[0] = SYNC_BYTE_OUT;
buf[1] = id;
buf[2] = PCTV_CMD_I2C;
@@ -466,7 +467,7 @@ static int pctv452e_i2c_msg(struct dvb_usb_device *d, u8 addr,
failed:
err("I2C error %d; %02X %02X %02X %02X %02X -> %*ph",
ret, SYNC_BYTE_OUT, id, addr << 1, snd_len, rcv_len,
- 7, buf);
+ plen, buf);

kfree(buf);
return ret;
--
2.43.0