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

[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+480edd2cadb85ddb4bbe@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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[PATCH] meida: dvb-usb: Optimizing err() output

[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+480edd2cadb85ddb4bbe@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=480edd2cadb85ddb4bbe
Signed-off-by: Edward Adam Davis <eadavis@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

[PATCH V2] media: dvb-usb: Optimizing err() output

[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+480edd2cadb85ddb4bbe@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=480edd2cadb85ddb4bbe
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
V1 -> V2: subject typos

 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

Re: [PATCH V2] media: dvb-usb: Optimizing err() output

[Hans Verkuil]

On 14/10/2025 02:30, Edward Adam Davis wrote:
> 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+480edd2cadb85ddb4bbe@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=480edd2cadb85ddb4bbe
> Signed-off-by: Edward Adam Davis <eadavis@qq.com>
> ---
> V1 -> V2: subject typos
> 
>  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;

Adding a plen variable isn't the right fix...

>  
>  	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;

...this check should be moved up to before the kmalloc and just return -EINVAL.
That also avoids incrementing state->c in that case.

Regards,

	Hans

>  
> +	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;

Re: [PATCH V2] media: dvb-usb: Optimizing err() output

[Hans Verkuil]

Also fix the Subject line to add "pctv452e:" as prefix.

Regards,

	Hans

On 03/11/2025 12:00, Hans Verkuil wrote:
> On 14/10/2025 02:30, Edward Adam Davis wrote:
>> 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+480edd2cadb85ddb4bbe@syzkaller.appspotmail.com
>> Closes: https://syzkaller.appspot.com/bug?extid=480edd2cadb85ddb4bbe
>> Signed-off-by: Edward Adam Davis <eadavis@qq.com>
>> ---
>> V1 -> V2: subject typos
>>
>>  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;
> 
> Adding a plen variable isn't the right fix...
> 
>>  
>>  	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;
> 
> ...this check should be moved up to before the kmalloc and just return -EINVAL.
> That also avoids incrementing state->c in that case.
> 
> Regards,
> 
> 	Hans
> 
>>  
>> +	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;
> 
> 

[PATCH V3] media: dvb-usb: pctv452e: move snd/rcv len check before kmalloc

[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.

Move the snd/rcv length check before kmalloc, and return -EINVAL directly
if the condition is met.

[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+480edd2cadb85ddb4bbe@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=480edd2cadb85ddb4bbe
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
V1 -> V2: subject typos
V2 -> V3: move the check before kmalloc

 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..bc7a224d829e 100644
--- a/drivers/media/usb/dvb-usb/pctv452e.c
+++ b/drivers/media/usb/dvb-usb/pctv452e.c
@@ -422,16 +422,15 @@ static int pctv452e_i2c_msg(struct dvb_usb_device *d, u8 addr,
 	u8 id;
 	int ret;
 
+	if (snd_len > 64 - 7 || rcv_len > 64 - 7)
+		return -EINVAL;
+
 	buf = kmalloc(64, GFP_KERNEL);
 	if (!buf)
 		return -ENOMEM;
 
 	id = state->c++;
 
-	ret = -EINVAL;
-	if (snd_len > 64 - 7 || rcv_len > 64 - 7)
-		goto failed;
-
 	buf[0] = SYNC_BYTE_OUT;
 	buf[1] = id;
 	buf[2] = PCTV_CMD_I2C;
-- 
2.43.0