[PATCH v2] PCI/proc: check user access return values in proc_bus_pci_{read,write}()

[PATCH v2] PCI/proc: check user access return values in proc_bus_pci_{read,write}()

[Deepanshu Kartikey]

proc_bus_pci_write() ignores the return value of __get_user(). On a
faulting user pointer the extable fixup zeros the destination, and the
function writes those zeros to PCI configuration space.

syzbot triggers this with writev()-ing a NULL iov_base to
/proc/bus/pci/00/03.0 (the virtio-blk controller in the syzkaller VM):
zero is written to the Command register, clearing Bus Master Enable,
and the disk stops responding. In-flight journal writes never complete
and jbd2 hangs in wait_on_buffer() indefinitely:

  INFO: task jbd2/sda1-8 blocked in I/O wait for more than 143 seconds.
   __wait_on_buffer fs/buffer.c:123
   jbd2_journal_commit_transaction+0x388a/0x6870 fs/jbd2/commit.c:837
   kjournald2 fs/jbd2/journal.c:201

proc_bus_pci_read() has the symmetric problem with __put_user(): a
faulting user pointer silently drops config-space data and returns
success.

Switch both functions to get_user()/put_user(), which combine the
access_ok() check with the load/store and return -EFAULT on failure.
The up-front access_ok() can be removed accordingly. On error, jump to
a common label that releases the runtime-PM reference and returns
-EFAULT.

Reported-by: syzbot+c7604c9fdd7580cca4e0@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=c7604c9fdd7580cca4e0
Tested-by: syzbot+c7604c9fdd7580cca4e0@syzkaller.appspotmail.com
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
Changes in v2:
 - Use get_user()/put_user() and drop access_ok() (Krzysztof)
 - Rename label to err: per kernel convention (Krzysztof)
 - Simplify error path to release runtime-PM and return -EFAULT (Krzysztof)
 - Apply the same fix to proc_bus_pci_read() (Krzysztof)
---
 drivers/pci/proc.c | 44 ++++++++++++++++++++++++++++----------------
 1 file changed, 28 insertions(+), 16 deletions(-)

diff --git a/drivers/pci/proc.c b/drivers/pci/proc.c
index ce36e35681e8..8e624d829840 100644
--- a/drivers/pci/proc.c
+++ b/drivers/pci/proc.c
@@ -53,15 +53,13 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
 		nbytes = size - pos;
 	cnt = nbytes;
 
-	if (!access_ok(buf, cnt))
-		return -EINVAL;
-
 	pci_config_pm_runtime_get(dev);
 
 	if ((pos & 1) && cnt) {
 		unsigned char val;
 		pci_user_read_config_byte(dev, pos, &val);
-		__put_user(val, buf);
+		if (put_user(val, buf))
+			goto err;
 		buf++;
 		pos++;
 		cnt--;
@@ -70,7 +68,8 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
 	if ((pos & 3) && cnt > 2) {
 		unsigned short val;
 		pci_user_read_config_word(dev, pos, &val);
-		__put_user(cpu_to_le16(val), (__le16 __user *) buf);
+		if (put_user(cpu_to_le16(val), (__le16 __user *) buf))
+			goto err;
 		buf += 2;
 		pos += 2;
 		cnt -= 2;
@@ -79,7 +78,8 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
 	while (cnt >= 4) {
 		unsigned int val;
 		pci_user_read_config_dword(dev, pos, &val);
-		__put_user(cpu_to_le32(val), (__le32 __user *) buf);
+		if (put_user(cpu_to_le32(val), (__le32 __user *) buf))
+			goto err;
 		buf += 4;
 		pos += 4;
 		cnt -= 4;
@@ -89,7 +89,8 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
 	if (cnt >= 2) {
 		unsigned short val;
 		pci_user_read_config_word(dev, pos, &val);
-		__put_user(cpu_to_le16(val), (__le16 __user *) buf);
+		if (put_user(cpu_to_le16(val), (__le16 __user *) buf))
+			goto err;
 		buf += 2;
 		pos += 2;
 		cnt -= 2;
@@ -98,7 +99,8 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
 	if (cnt) {
 		unsigned char val;
 		pci_user_read_config_byte(dev, pos, &val);
-		__put_user(val, buf);
+		if (put_user(val, buf))
+			goto err;
 		pos++;
 	}
 
@@ -106,6 +108,10 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
 
 	*ppos = pos;
 	return nbytes;
+
+err:
+	pci_config_pm_runtime_put(dev);
+	return -EFAULT;
 }
 
 static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
@@ -129,14 +135,12 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
 		nbytes = size - pos;
 	cnt = nbytes;
 
-	if (!access_ok(buf, cnt))
-		return -EINVAL;
-
 	pci_config_pm_runtime_get(dev);
 
 	if ((pos & 1) && cnt) {
 		unsigned char val;
-		__get_user(val, buf);
+		if (get_user(val, buf))
+			goto err;
 		pci_user_write_config_byte(dev, pos, val);
 		buf++;
 		pos++;
@@ -145,7 +149,8 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
 
 	if ((pos & 3) && cnt > 2) {
 		__le16 val;
-		__get_user(val, (__le16 __user *) buf);
+		if (get_user(val, (__le16 __user *) buf))
+			goto err;
 		pci_user_write_config_word(dev, pos, le16_to_cpu(val));
 		buf += 2;
 		pos += 2;
@@ -154,7 +159,8 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
 
 	while (cnt >= 4) {
 		__le32 val;
-		__get_user(val, (__le32 __user *) buf);
+		if (get_user(val, (__le32 __user *) buf))
+			goto err;
 		pci_user_write_config_dword(dev, pos, le32_to_cpu(val));
 		buf += 4;
 		pos += 4;
@@ -163,7 +169,8 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
 
 	if (cnt >= 2) {
 		__le16 val;
-		__get_user(val, (__le16 __user *) buf);
+		if (get_user(val, (__le16 __user *) buf))
+			goto err;
 		pci_user_write_config_word(dev, pos, le16_to_cpu(val));
 		buf += 2;
 		pos += 2;
@@ -172,7 +179,8 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
 
 	if (cnt) {
 		unsigned char val;
-		__get_user(val, buf);
+		if (get_user(val, buf))
+			goto err;
 		pci_user_write_config_byte(dev, pos, val);
 		pos++;
 	}
@@ -182,6 +190,10 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
 	*ppos = pos;
 	i_size_write(ino, dev->cfg_size);
 	return nbytes;
+
+err:
+	pci_config_pm_runtime_put(dev);
+	return -EFAULT;
 }
 
 #ifdef HAVE_PCI_MMAP
-- 
2.43.0

Re: [PATCH v2] PCI/proc: check user access return values in proc_bus_pci_{read,write}()

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [High] Integer truncation in proc_bus_pci_write allows negative offsets to bypass bounds checks, leading to out-of-bounds PCI accesses and soft lockups.
- [Medium] Error handling discards partial transfers, violating POSIX semantics and risking unintended side effects on retry.
--

commit e7bdf9d788abd98223b783ee67cefeac2bfdde52
Author: Deepanshu Kartikey <kartikey406@gmail.com>

PCI/proc: check user access return values in proc_bus_pci_{read,write}()

This commit replaces __get_user() and __put_user() with get_user() and
put_user() to check for user access faults during PCI config space reads
and writes. It removes the upfront access_ok() check and adds an error
path to release the runtime PM reference and return -EFAULT on failure.

> diff --git a/drivers/pci/proc.c b/drivers/pci/proc.c
> index ce36e35681e8..8e624d829840 100644
> --- a/drivers/pci/proc.c
> +++ b/drivers/pci/proc.c
> @@ -53,15 +53,13 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
>  		nbytes = size - pos;
>  	cnt = nbytes;
>  
> -	if (!access_ok(buf, cnt))
> -		return -EINVAL;
> -
>  	pci_config_pm_runtime_get(dev);
>  
>  	if ((pos & 1) && cnt) {
>  		unsigned char val;
>  		pci_user_read_config_byte(dev, pos, &val);
> -		__put_user(val, buf);
> +		if (put_user(val, buf))
> +			goto err;
>  		buf++;
>  		pos++;
>  		cnt--;
> @@ -70,7 +68,8 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
>  	if ((pos & 3) && cnt > 2) {
>  		unsigned short val;
>  		pci_user_read_config_word(dev, pos, &val);
> -		__put_user(cpu_to_le16(val), (__le16 __user *) buf);
> +		if (put_user(cpu_to_le16(val), (__le16 __user *) buf))
> +			goto err;

If a fault happens during this put_user() call, some bytes may have already
been successfully transferred by the previous call. Unconditionally jumping
to the err label and returning -EFAULT discards this partial progress and
fails to update *ppos.

Since configuration registers can be stateful, such as Write-1-to-Clear
bits, could userspace retrying the entire operation cause unintended side
effects?

If data has been successfully processed prior to a fault, should the function
update the file offset and return the number of bytes transferred instead?

[ ... ]
> @@ -106,6 +108,10 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
>  
>  	*ppos = pos;
>  	return nbytes;
> +
> +err:
> +	pci_config_pm_runtime_put(dev);
> +	return -EFAULT;
>  }
>  
>  static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,

This issue isn't introduced by the patch, but does this function truncate
*ppos? Looking at the full function:

static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
				  size_t nbytes, loff_t *ppos)
{
	...
	int pos = *ppos;
	...

If a large positive offset is passed, such as 2294967296, the assignment to
the 32-bit int pos would truncate it to a negative value.

This bypasses the if (pos >= size) check. When checking pos + nbytes > size,
pos is promoted to a 64-bit size_t and sign-extends to a huge value, making
the condition true. nbytes is then calculated as size - pos, resulting in a
massive positive integer for cnt.

[ ... ]
> @@ -154,7 +159,8 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
>  
>  	while (cnt >= 4) {
>  		__le32 val;
> -		__get_user(val, (__le32 __user *) buf);
> +		if (get_user(val, (__le32 __user *) buf))
> +			goto err;
>  		pci_user_write_config_dword(dev, pos, le32_to_cpu(val));
>  		buf += 4;
>  		pos += 4;
>  		cnt -= 4;

The while (cnt >= 4) loop would then execute hundreds of millions of times,
passing a negative offset to the configuration accessor functions.

Since proc_bus_pci_write() lacks a cond_resched() call in this loop, could
this trigger a soft lockup?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260504022231.15501-1-kartikey406@gmail.com?part=1

Re: [PATCH v2] PCI/proc: check user access return values in proc_bus_pci_{read,write}()

[Deepanshu Kartikey]

On Mon, May 4, 2026 at 7:52 AM Deepanshu Kartikey <kartikey406@gmail.com> wrote:
>
> proc_bus_pci_write() ignores the return value of __get_user(). On a
> faulting user pointer the extable fixup zeros the destination, and the
> function writes those zeros to PCI configuration space.
>
> syzbot triggers this with writev()-ing a NULL iov_base to
> /proc/bus/pci/00/03.0 (the virtio-blk controller in the syzkaller VM):
> zero is written to the Command register, clearing Bus Master Enable,
> and the disk stops responding. In-flight journal writes never complete
> and jbd2 hangs in wait_on_buffer() indefinitely:
>
>   INFO: task jbd2/sda1-8 blocked in I/O wait for more than 143 seconds.
>    __wait_on_buffer fs/buffer.c:123
>    jbd2_journal_commit_transaction+0x388a/0x6870 fs/jbd2/commit.c:837
>    kjournald2 fs/jbd2/journal.c:201
>
> proc_bus_pci_read() has the symmetric problem with __put_user(): a
> faulting user pointer silently drops config-space data and returns
> success.
>
> Switch both functions to get_user()/put_user(), which combine the
> access_ok() check with the load/store and return -EFAULT on failure.
> The up-front access_ok() can be removed accordingly. On error, jump to
> a common label that releases the runtime-PM reference and returns
> -EFAULT.
>
> Reported-by: syzbot+c7604c9fdd7580cca4e0@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=c7604c9fdd7580cca4e0
> Tested-by: syzbot+c7604c9fdd7580cca4e0@syzkaller.appspotmail.com
> Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
> ---
> Changes in v2:
>  - Use get_user()/put_user() and drop access_ok() (Krzysztof)
>  - Rename label to err: per kernel convention (Krzysztof)
>  - Simplify error path to release runtime-PM and return -EFAULT (Krzysztof)
>  - Apply the same fix to proc_bus_pci_read() (Krzysztof)
> ---
>  drivers/pci/proc.c | 44 ++++++++++++++++++++++++++++----------------
>  1 file changed, 28 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/pci/proc.c b/drivers/pci/proc.c
> index ce36e35681e8..8e624d829840 100644
> --- a/drivers/pci/proc.c
> +++ b/drivers/pci/proc.c
> @@ -53,15 +53,13 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
>                 nbytes = size - pos;
>         cnt = nbytes;
>
> -       if (!access_ok(buf, cnt))
> -               return -EINVAL;
> -
>         pci_config_pm_runtime_get(dev);
>
>         if ((pos & 1) && cnt) {
>                 unsigned char val;
>                 pci_user_read_config_byte(dev, pos, &val);
> -               __put_user(val, buf);
> +               if (put_user(val, buf))
> +                       goto err;
>                 buf++;
>                 pos++;
>                 cnt--;
> @@ -70,7 +68,8 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
>         if ((pos & 3) && cnt > 2) {
>                 unsigned short val;
>                 pci_user_read_config_word(dev, pos, &val);
> -               __put_user(cpu_to_le16(val), (__le16 __user *) buf);
> +               if (put_user(cpu_to_le16(val), (__le16 __user *) buf))
> +                       goto err;
>                 buf += 2;
>                 pos += 2;
>                 cnt -= 2;
> @@ -79,7 +78,8 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
>         while (cnt >= 4) {
>                 unsigned int val;
>                 pci_user_read_config_dword(dev, pos, &val);
> -               __put_user(cpu_to_le32(val), (__le32 __user *) buf);
> +               if (put_user(cpu_to_le32(val), (__le32 __user *) buf))
> +                       goto err;
>                 buf += 4;
>                 pos += 4;
>                 cnt -= 4;
> @@ -89,7 +89,8 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
>         if (cnt >= 2) {
>                 unsigned short val;
>                 pci_user_read_config_word(dev, pos, &val);
> -               __put_user(cpu_to_le16(val), (__le16 __user *) buf);
> +               if (put_user(cpu_to_le16(val), (__le16 __user *) buf))
> +                       goto err;
>                 buf += 2;
>                 pos += 2;
>                 cnt -= 2;
> @@ -98,7 +99,8 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
>         if (cnt) {
>                 unsigned char val;
>                 pci_user_read_config_byte(dev, pos, &val);
> -               __put_user(val, buf);
> +               if (put_user(val, buf))
> +                       goto err;
>                 pos++;
>         }
>
> @@ -106,6 +108,10 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
>
>         *ppos = pos;
>         return nbytes;
> +
> +err:
> +       pci_config_pm_runtime_put(dev);
> +       return -EFAULT;
>  }
>
>  static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
> @@ -129,14 +135,12 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
>                 nbytes = size - pos;
>         cnt = nbytes;
>
> -       if (!access_ok(buf, cnt))
> -               return -EINVAL;
> -
>         pci_config_pm_runtime_get(dev);
>
>         if ((pos & 1) && cnt) {
>                 unsigned char val;
> -               __get_user(val, buf);
> +               if (get_user(val, buf))
> +                       goto err;
>                 pci_user_write_config_byte(dev, pos, val);
>                 buf++;
>                 pos++;
> @@ -145,7 +149,8 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
>
>         if ((pos & 3) && cnt > 2) {
>                 __le16 val;
> -               __get_user(val, (__le16 __user *) buf);
> +               if (get_user(val, (__le16 __user *) buf))
> +                       goto err;
>                 pci_user_write_config_word(dev, pos, le16_to_cpu(val));
>                 buf += 2;
>                 pos += 2;
> @@ -154,7 +159,8 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
>
>         while (cnt >= 4) {
>                 __le32 val;
> -               __get_user(val, (__le32 __user *) buf);
> +               if (get_user(val, (__le32 __user *) buf))
> +                       goto err;
>                 pci_user_write_config_dword(dev, pos, le32_to_cpu(val));
>                 buf += 4;
>                 pos += 4;
> @@ -163,7 +169,8 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
>
>         if (cnt >= 2) {
>                 __le16 val;
> -               __get_user(val, (__le16 __user *) buf);
> +               if (get_user(val, (__le16 __user *) buf))
> +                       goto err;
>                 pci_user_write_config_word(dev, pos, le16_to_cpu(val));
>                 buf += 2;
>                 pos += 2;
> @@ -172,7 +179,8 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
>
>         if (cnt) {
>                 unsigned char val;
> -               __get_user(val, buf);
> +               if (get_user(val, buf))
> +                       goto err;
>                 pci_user_write_config_byte(dev, pos, val);
>                 pos++;
>         }
> @@ -182,6 +190,10 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
>         *ppos = pos;
>         i_size_write(ino, dev->cfg_size);
>         return nbytes;
> +
> +err:
> +       pci_config_pm_runtime_put(dev);
> +       return -EFAULT;
>  }
>
>  #ifdef HAVE_PCI_MMAP
> --
> 2.43.0
>

Gentle Reminder on this patch. Please let me know the status of this patch.

Thanks

Deepanshu Kartikey

Re: [PATCH v2] PCI/proc: check user access return values in proc_bus_pci_{read,write}()

[Bjorn Helgaas]

On Sun, Jun 21, 2026 at 01:52:17PM +0530, Deepanshu Kartikey wrote:
> On Mon, May 4, 2026 at 7:52 AM Deepanshu Kartikey <kartikey406@gmail.com> wrote:
> >
> > proc_bus_pci_write() ignores the return value of __get_user(). On a
> > faulting user pointer the extable fixup zeros the destination, and the
> > function writes those zeros to PCI configuration space.
> >
> > syzbot triggers this with writev()-ing a NULL iov_base to
> > /proc/bus/pci/00/03.0 (the virtio-blk controller in the syzkaller VM):
> > zero is written to the Command register, clearing Bus Master Enable,
> > and the disk stops responding. In-flight journal writes never complete
> > and jbd2 hangs in wait_on_buffer() indefinitely:
> >
> >   INFO: task jbd2/sda1-8 blocked in I/O wait for more than 143 seconds.
> >    __wait_on_buffer fs/buffer.c:123
> >    jbd2_journal_commit_transaction+0x388a/0x6870 fs/jbd2/commit.c:837
> >    kjournald2 fs/jbd2/journal.c:201
> >
> > proc_bus_pci_read() has the symmetric problem with __put_user(): a
> > faulting user pointer silently drops config-space data and returns
> > success.
> >
> > Switch both functions to get_user()/put_user(), which combine the
> > access_ok() check with the load/store and return -EFAULT on failure.
> > The up-front access_ok() can be removed accordingly. On error, jump to
> > a common label that releases the runtime-PM reference and returns
> > -EFAULT.
> >
> > Reported-by: syzbot+c7604c9fdd7580cca4e0@syzkaller.appspotmail.com
> > Closes: https://syzkaller.appspot.com/bug?extid=c7604c9fdd7580cca4e0
> > Tested-by: syzbot+c7604c9fdd7580cca4e0@syzkaller.appspotmail.com
> > Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
> > ---
> > Changes in v2:
> >  - Use get_user()/put_user() and drop access_ok() (Krzysztof)
> >  - Rename label to err: per kernel convention (Krzysztof)
> >  - Simplify error path to release runtime-PM and return -EFAULT (Krzysztof)
> >  - Apply the same fix to proc_bus_pci_read() (Krzysztof)
> > ---
> >  drivers/pci/proc.c | 44 ++++++++++++++++++++++++++++----------------
> >  1 file changed, 28 insertions(+), 16 deletions(-)
> >
> > diff --git a/drivers/pci/proc.c b/drivers/pci/proc.c
> > index ce36e35681e8..8e624d829840 100644
> > --- a/drivers/pci/proc.c
> > +++ b/drivers/pci/proc.c
> > @@ -53,15 +53,13 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
> >                 nbytes = size - pos;
> >         cnt = nbytes;
> >
> > -       if (!access_ok(buf, cnt))
> > -               return -EINVAL;
> > -
> >         pci_config_pm_runtime_get(dev);
> >
> >         if ((pos & 1) && cnt) {
> >                 unsigned char val;
> >                 pci_user_read_config_byte(dev, pos, &val);
> > -               __put_user(val, buf);
> > +               if (put_user(val, buf))
> > +                       goto err;
> >                 buf++;
> >                 pos++;
> >                 cnt--;
> > @@ -70,7 +68,8 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
> >         if ((pos & 3) && cnt > 2) {
> >                 unsigned short val;
> >                 pci_user_read_config_word(dev, pos, &val);
> > -               __put_user(cpu_to_le16(val), (__le16 __user *) buf);
> > +               if (put_user(cpu_to_le16(val), (__le16 __user *) buf))
> > +                       goto err;
> >                 buf += 2;
> >                 pos += 2;
> >                 cnt -= 2;
> > @@ -79,7 +78,8 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
> >         while (cnt >= 4) {
> >                 unsigned int val;
> >                 pci_user_read_config_dword(dev, pos, &val);
> > -               __put_user(cpu_to_le32(val), (__le32 __user *) buf);
> > +               if (put_user(cpu_to_le32(val), (__le32 __user *) buf))
> > +                       goto err;
> >                 buf += 4;
> >                 pos += 4;
> >                 cnt -= 4;
> > @@ -89,7 +89,8 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
> >         if (cnt >= 2) {
> >                 unsigned short val;
> >                 pci_user_read_config_word(dev, pos, &val);
> > -               __put_user(cpu_to_le16(val), (__le16 __user *) buf);
> > +               if (put_user(cpu_to_le16(val), (__le16 __user *) buf))
> > +                       goto err;
> >                 buf += 2;
> >                 pos += 2;
> >                 cnt -= 2;
> > @@ -98,7 +99,8 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
> >         if (cnt) {
> >                 unsigned char val;
> >                 pci_user_read_config_byte(dev, pos, &val);
> > -               __put_user(val, buf);
> > +               if (put_user(val, buf))
> > +                       goto err;
> >                 pos++;
> >         }
> >
> > @@ -106,6 +108,10 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
> >
> >         *ppos = pos;
> >         return nbytes;
> > +
> > +err:
> > +       pci_config_pm_runtime_put(dev);
> > +       return -EFAULT;
> >  }
> >
> >  static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
> > @@ -129,14 +135,12 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
> >                 nbytes = size - pos;
> >         cnt = nbytes;
> >
> > -       if (!access_ok(buf, cnt))
> > -               return -EINVAL;
> > -
> >         pci_config_pm_runtime_get(dev);
> >
> >         if ((pos & 1) && cnt) {
> >                 unsigned char val;
> > -               __get_user(val, buf);
> > +               if (get_user(val, buf))
> > +                       goto err;
> >                 pci_user_write_config_byte(dev, pos, val);
> >                 buf++;
> >                 pos++;
> > @@ -145,7 +149,8 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
> >
> >         if ((pos & 3) && cnt > 2) {
> >                 __le16 val;
> > -               __get_user(val, (__le16 __user *) buf);
> > +               if (get_user(val, (__le16 __user *) buf))
> > +                       goto err;
> >                 pci_user_write_config_word(dev, pos, le16_to_cpu(val));
> >                 buf += 2;
> >                 pos += 2;
> > @@ -154,7 +159,8 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
> >
> >         while (cnt >= 4) {
> >                 __le32 val;
> > -               __get_user(val, (__le32 __user *) buf);
> > +               if (get_user(val, (__le32 __user *) buf))
> > +                       goto err;
> >                 pci_user_write_config_dword(dev, pos, le32_to_cpu(val));
> >                 buf += 4;
> >                 pos += 4;
> > @@ -163,7 +169,8 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
> >
> >         if (cnt >= 2) {
> >                 __le16 val;
> > -               __get_user(val, (__le16 __user *) buf);
> > +               if (get_user(val, (__le16 __user *) buf))
> > +                       goto err;
> >                 pci_user_write_config_word(dev, pos, le16_to_cpu(val));
> >                 buf += 2;
> >                 pos += 2;
> > @@ -172,7 +179,8 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
> >
> >         if (cnt) {
> >                 unsigned char val;
> > -               __get_user(val, buf);
> > +               if (get_user(val, buf))
> > +                       goto err;
> >                 pci_user_write_config_byte(dev, pos, val);
> >                 pos++;
> >         }
> > @@ -182,6 +190,10 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
> >         *ppos = pos;
> >         i_size_write(ino, dev->cfg_size);
> >         return nbytes;
> > +
> > +err:
> > +       pci_config_pm_runtime_put(dev);
> > +       return -EFAULT;
> >  }
> >
> >  #ifdef HAVE_PCI_MMAP
> > --
> > 2.43.0
> >
> 
> Gentle Reminder on this patch. Please let me know the status of this
> patch.

Thanks for the reminder.  We're halfway through the merge window for
v7.2, so we'll have to look at this for v7.3 after v7.2-rc1 is tagged.

Re: [PATCH v2] PCI/proc: check user access return values in proc_bus_pci_{read,write}()

[Deepanshu Kartikey]

On Mon, Jun 22, 2026 at 10:49 PM Bjorn Helgaas <helgaas@kernel.org> wrote:
>
> On Sun, Jun 21, 2026 at 01:52:17PM +0530, Deepanshu Kartikey wrote:
> > On Mon, May 4, 2026 at 7:52 AM Deepanshu Kartikey <kartikey406@gmail.com> wrote:
> > >
> > > proc_bus_pci_write() ignores the return value of __get_user(). On a
> > > faulting user pointer the extable fixup zeros the destination, and the
> > > function writes those zeros to PCI configuration space.
> > >
> > > syzbot triggers this with writev()-ing a NULL iov_base to
> > > /proc/bus/pci/00/03.0 (the virtio-blk controller in the syzkaller VM):
> > > zero is written to the Command register, clearing Bus Master Enable,
> > > and the disk stops responding. In-flight journal writes never complete
> > > and jbd2 hangs in wait_on_buffer() indefinitely:
> > >
> > >   INFO: task jbd2/sda1-8 blocked in I/O wait for more than 143 seconds.
> > >    __wait_on_buffer fs/buffer.c:123
> > >    jbd2_journal_commit_transaction+0x388a/0x6870 fs/jbd2/commit.c:837
> > >    kjournald2 fs/jbd2/journal.c:201
> > >
> > > proc_bus_pci_read() has the symmetric problem with __put_user(): a
> > > faulting user pointer silently drops config-space data and returns
> > > success.
> > >
> > > Switch both functions to get_user()/put_user(), which combine the
> > > access_ok() check with the load/store and return -EFAULT on failure.
> > > The up-front access_ok() can be removed accordingly. On error, jump to
> > > a common label that releases the runtime-PM reference and returns
> > > -EFAULT.
> > >
> > > Reported-by: syzbot+c7604c9fdd7580cca4e0@syzkaller.appspotmail.com
> > > Closes: https://syzkaller.appspot.com/bug?extid=c7604c9fdd7580cca4e0
> > > Tested-by: syzbot+c7604c9fdd7580cca4e0@syzkaller.appspotmail.com
> > > Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
> > > ---
> > > Changes in v2:
> > >  - Use get_user()/put_user() and drop access_ok() (Krzysztof)
> > >  - Rename label to err: per kernel convention (Krzysztof)
> > >  - Simplify error path to release runtime-PM and return -EFAULT (Krzysztof)
> > >  - Apply the same fix to proc_bus_pci_read() (Krzysztof)
> > > ---
> > >  drivers/pci/proc.c | 44 ++++++++++++++++++++++++++++----------------
> > >  1 file changed, 28 insertions(+), 16 deletions(-)
> > >
> > > diff --git a/drivers/pci/proc.c b/drivers/pci/proc.c
> > > index ce36e35681e8..8e624d829840 100644
> > > --- a/drivers/pci/proc.c
> > > +++ b/drivers/pci/proc.c
> > > @@ -53,15 +53,13 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
> > >                 nbytes = size - pos;
> > >         cnt = nbytes;
> > >
> > > -       if (!access_ok(buf, cnt))
> > > -               return -EINVAL;
> > > -
> > >         pci_config_pm_runtime_get(dev);
> > >
> > >         if ((pos & 1) && cnt) {
> > >                 unsigned char val;
> > >                 pci_user_read_config_byte(dev, pos, &val);
> > > -               __put_user(val, buf);
> > > +               if (put_user(val, buf))
> > > +                       goto err;
> > >                 buf++;
> > >                 pos++;
> > >                 cnt--;
> > > @@ -70,7 +68,8 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
> > >         if ((pos & 3) && cnt > 2) {
> > >                 unsigned short val;
> > >                 pci_user_read_config_word(dev, pos, &val);
> > > -               __put_user(cpu_to_le16(val), (__le16 __user *) buf);
> > > +               if (put_user(cpu_to_le16(val), (__le16 __user *) buf))
> > > +                       goto err;
> > >                 buf += 2;
> > >                 pos += 2;
> > >                 cnt -= 2;
> > > @@ -79,7 +78,8 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
> > >         while (cnt >= 4) {
> > >                 unsigned int val;
> > >                 pci_user_read_config_dword(dev, pos, &val);
> > > -               __put_user(cpu_to_le32(val), (__le32 __user *) buf);
> > > +               if (put_user(cpu_to_le32(val), (__le32 __user *) buf))
> > > +                       goto err;
> > >                 buf += 4;
> > >                 pos += 4;
> > >                 cnt -= 4;
> > > @@ -89,7 +89,8 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
> > >         if (cnt >= 2) {
> > >                 unsigned short val;
> > >                 pci_user_read_config_word(dev, pos, &val);
> > > -               __put_user(cpu_to_le16(val), (__le16 __user *) buf);
> > > +               if (put_user(cpu_to_le16(val), (__le16 __user *) buf))
> > > +                       goto err;
> > >                 buf += 2;
> > >                 pos += 2;
> > >                 cnt -= 2;
> > > @@ -98,7 +99,8 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
> > >         if (cnt) {
> > >                 unsigned char val;
> > >                 pci_user_read_config_byte(dev, pos, &val);
> > > -               __put_user(val, buf);
> > > +               if (put_user(val, buf))
> > > +                       goto err;
> > >                 pos++;
> > >         }
> > >
> > > @@ -106,6 +108,10 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
> > >
> > >         *ppos = pos;
> > >         return nbytes;
> > > +
> > > +err:
> > > +       pci_config_pm_runtime_put(dev);
> > > +       return -EFAULT;
> > >  }
> > >
> > >  static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
> > > @@ -129,14 +135,12 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
> > >                 nbytes = size - pos;
> > >         cnt = nbytes;
> > >
> > > -       if (!access_ok(buf, cnt))
> > > -               return -EINVAL;
> > > -
> > >         pci_config_pm_runtime_get(dev);
> > >
> > >         if ((pos & 1) && cnt) {
> > >                 unsigned char val;
> > > -               __get_user(val, buf);
> > > +               if (get_user(val, buf))
> > > +                       goto err;
> > >                 pci_user_write_config_byte(dev, pos, val);
> > >                 buf++;
> > >                 pos++;
> > > @@ -145,7 +149,8 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
> > >
> > >         if ((pos & 3) && cnt > 2) {
> > >                 __le16 val;
> > > -               __get_user(val, (__le16 __user *) buf);
> > > +               if (get_user(val, (__le16 __user *) buf))
> > > +                       goto err;
> > >                 pci_user_write_config_word(dev, pos, le16_to_cpu(val));
> > >                 buf += 2;
> > >                 pos += 2;
> > > @@ -154,7 +159,8 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
> > >
> > >         while (cnt >= 4) {
> > >                 __le32 val;
> > > -               __get_user(val, (__le32 __user *) buf);
> > > +               if (get_user(val, (__le32 __user *) buf))
> > > +                       goto err;
> > >                 pci_user_write_config_dword(dev, pos, le32_to_cpu(val));
> > >                 buf += 4;
> > >                 pos += 4;
> > > @@ -163,7 +169,8 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
> > >
> > >         if (cnt >= 2) {
> > >                 __le16 val;
> > > -               __get_user(val, (__le16 __user *) buf);
> > > +               if (get_user(val, (__le16 __user *) buf))
> > > +                       goto err;
> > >                 pci_user_write_config_word(dev, pos, le16_to_cpu(val));
> > >                 buf += 2;
> > >                 pos += 2;
> > > @@ -172,7 +179,8 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
> > >
> > >         if (cnt) {
> > >                 unsigned char val;
> > > -               __get_user(val, buf);
> > > +               if (get_user(val, buf))
> > > +                       goto err;
> > >                 pci_user_write_config_byte(dev, pos, val);
> > >                 pos++;
> > >         }
> > > @@ -182,6 +190,10 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
> > >         *ppos = pos;
> > >         i_size_write(ino, dev->cfg_size);
> > >         return nbytes;
> > > +
> > > +err:
> > > +       pci_config_pm_runtime_put(dev);
> > > +       return -EFAULT;
> > >  }
> > >
> > >  #ifdef HAVE_PCI_MMAP
> > > --
> > > 2.43.0
> > >
> >
> > Gentle Reminder on this patch. Please let me know the status of this
> > patch.
>
> Thanks for the reminder.  We're halfway through the merge window for
> v7.2, so we'll have to look at this for v7.3 after v7.2-rc1 is tagged.

Hi Bjorn,

Any update on this patch ?

Thanks

Deepanshu

Re: [PATCH v2] PCI/proc: check user access return values in proc_bus_pci_{read,write}()

[Bjorn Helgaas]

On Mon, May 04, 2026 at 07:52:31AM +0530, Deepanshu Kartikey wrote:
> proc_bus_pci_write() ignores the return value of __get_user(). On a
> faulting user pointer the extable fixup zeros the destination, and the
> function writes those zeros to PCI configuration space.
> 
> syzbot triggers this with writev()-ing a NULL iov_base to
> /proc/bus/pci/00/03.0 (the virtio-blk controller in the syzkaller VM):
> zero is written to the Command register, clearing Bus Master Enable,
> and the disk stops responding. In-flight journal writes never complete
> and jbd2 hangs in wait_on_buffer() indefinitely:
> 
>   INFO: task jbd2/sda1-8 blocked in I/O wait for more than 143 seconds.
>    __wait_on_buffer fs/buffer.c:123
>    jbd2_journal_commit_transaction+0x388a/0x6870 fs/jbd2/commit.c:837
>    kjournald2 fs/jbd2/journal.c:201
> 
> proc_bus_pci_read() has the symmetric problem with __put_user(): a
> faulting user pointer silently drops config-space data and returns
> success.
> 
> Switch both functions to get_user()/put_user(), which combine the
> access_ok() check with the load/store and return -EFAULT on failure.
> The up-front access_ok() can be removed accordingly. On error, jump to
> a common label that releases the runtime-PM reference and returns
> -EFAULT.
> 
> Reported-by: syzbot+c7604c9fdd7580cca4e0@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=c7604c9fdd7580cca4e0
> Tested-by: syzbot+c7604c9fdd7580cca4e0@syzkaller.appspotmail.com
> Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>

Thanks for this patch!

I asked gemini to reduce the syzbot repro details and focus on the
issues of writing bogus data to config space, returning success with
invalid read data, and returning -EFAULT.  It suggested the log below;
what do you think?

  PCI/proc: Return -EFAULT on get_user() and put_user() failures

  proc_bus_pci_write() ignores the return value of __get_user(). On a
  faulting user-space pointer, the exception table fixup zeros the
  destination, and proc_bus_pci_write() writes those invalid zeros
  into PCI configuration space.

  proc_bus_pci_read() ignores the return value of __put_user(). On a
  faulting user-space pointer, it fails to copy the PCI configuration
  space data to user space but still returns success.

  Fix both issues by:

    - Switching to get_user() and put_user() and checking return values

    - Returning -EFAULT, not -EINVAL, when get_user() or put_user() fails

    - Removing the redundant access_ok() checks, since get_user() and
      put_user() validate access internally

> ---
> Changes in v2:
>  - Use get_user()/put_user() and drop access_ok() (Krzysztof)
>  - Rename label to err: per kernel convention (Krzysztof)
>  - Simplify error path to release runtime-PM and return -EFAULT (Krzysztof)
>  - Apply the same fix to proc_bus_pci_read() (Krzysztof)
> ---
>  drivers/pci/proc.c | 44 ++++++++++++++++++++++++++++----------------
>  1 file changed, 28 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/pci/proc.c b/drivers/pci/proc.c
> index ce36e35681e8..8e624d829840 100644
> --- a/drivers/pci/proc.c
> +++ b/drivers/pci/proc.c
> @@ -53,15 +53,13 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
>  		nbytes = size - pos;
>  	cnt = nbytes;
>  
> -	if (!access_ok(buf, cnt))
> -		return -EINVAL;
> -
>  	pci_config_pm_runtime_get(dev);
>  
>  	if ((pos & 1) && cnt) {
>  		unsigned char val;
>  		pci_user_read_config_byte(dev, pos, &val);
> -		__put_user(val, buf);
> +		if (put_user(val, buf))
> +			goto err;
>  		buf++;
>  		pos++;
>  		cnt--;
> @@ -70,7 +68,8 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
>  	if ((pos & 3) && cnt > 2) {
>  		unsigned short val;
>  		pci_user_read_config_word(dev, pos, &val);
> -		__put_user(cpu_to_le16(val), (__le16 __user *) buf);
> +		if (put_user(cpu_to_le16(val), (__le16 __user *) buf))
> +			goto err;
>  		buf += 2;
>  		pos += 2;
>  		cnt -= 2;
> @@ -79,7 +78,8 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
>  	while (cnt >= 4) {
>  		unsigned int val;
>  		pci_user_read_config_dword(dev, pos, &val);
> -		__put_user(cpu_to_le32(val), (__le32 __user *) buf);
> +		if (put_user(cpu_to_le32(val), (__le32 __user *) buf))
> +			goto err;
>  		buf += 4;
>  		pos += 4;
>  		cnt -= 4;
> @@ -89,7 +89,8 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
>  	if (cnt >= 2) {
>  		unsigned short val;
>  		pci_user_read_config_word(dev, pos, &val);
> -		__put_user(cpu_to_le16(val), (__le16 __user *) buf);
> +		if (put_user(cpu_to_le16(val), (__le16 __user *) buf))
> +			goto err;
>  		buf += 2;
>  		pos += 2;
>  		cnt -= 2;
> @@ -98,7 +99,8 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
>  	if (cnt) {
>  		unsigned char val;
>  		pci_user_read_config_byte(dev, pos, &val);
> -		__put_user(val, buf);
> +		if (put_user(val, buf))
> +			goto err;
>  		pos++;
>  	}
>  
> @@ -106,6 +108,10 @@ static ssize_t proc_bus_pci_read(struct file *file, char __user *buf,
>  
>  	*ppos = pos;
>  	return nbytes;
> +
> +err:
> +	pci_config_pm_runtime_put(dev);
> +	return -EFAULT;
>  }
>  
>  static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
> @@ -129,14 +135,12 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
>  		nbytes = size - pos;
>  	cnt = nbytes;
>  
> -	if (!access_ok(buf, cnt))
> -		return -EINVAL;
> -
>  	pci_config_pm_runtime_get(dev);
>  
>  	if ((pos & 1) && cnt) {
>  		unsigned char val;
> -		__get_user(val, buf);
> +		if (get_user(val, buf))
> +			goto err;
>  		pci_user_write_config_byte(dev, pos, val);
>  		buf++;
>  		pos++;
> @@ -145,7 +149,8 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
>  
>  	if ((pos & 3) && cnt > 2) {
>  		__le16 val;
> -		__get_user(val, (__le16 __user *) buf);
> +		if (get_user(val, (__le16 __user *) buf))
> +			goto err;
>  		pci_user_write_config_word(dev, pos, le16_to_cpu(val));
>  		buf += 2;
>  		pos += 2;
> @@ -154,7 +159,8 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
>  
>  	while (cnt >= 4) {
>  		__le32 val;
> -		__get_user(val, (__le32 __user *) buf);
> +		if (get_user(val, (__le32 __user *) buf))
> +			goto err;
>  		pci_user_write_config_dword(dev, pos, le32_to_cpu(val));
>  		buf += 4;
>  		pos += 4;
> @@ -163,7 +169,8 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
>  
>  	if (cnt >= 2) {
>  		__le16 val;
> -		__get_user(val, (__le16 __user *) buf);
> +		if (get_user(val, (__le16 __user *) buf))
> +			goto err;
>  		pci_user_write_config_word(dev, pos, le16_to_cpu(val));
>  		buf += 2;
>  		pos += 2;
> @@ -172,7 +179,8 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
>  
>  	if (cnt) {
>  		unsigned char val;
> -		__get_user(val, buf);
> +		if (get_user(val, buf))
> +			goto err;
>  		pci_user_write_config_byte(dev, pos, val);
>  		pos++;
>  	}
> @@ -182,6 +190,10 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
>  	*ppos = pos;
>  	i_size_write(ino, dev->cfg_size);
>  	return nbytes;
> +
> +err:
> +	pci_config_pm_runtime_put(dev);
> +	return -EFAULT;
>  }
>  
>  #ifdef HAVE_PCI_MMAP
> -- 
> 2.43.0
> 

Re: [PATCH v2] PCI/proc: check user access return values in proc_bus_pci_{read,write}()

[Krzysztof Wilczyński]

Hello,

[...]
> Changes in v2:
>  - Use get_user()/put_user() and drop access_ok() (Krzysztof)
>  - Rename label to err: per kernel convention (Krzysztof)
>  - Simplify error path to release runtime-PM and return -EFAULT (Krzysztof)
>  - Apply the same fix to proc_bus_pci_read() (Krzysztof)

Looks good, and with changes to the commit log per Bjorn:

  Reviewed-by: Krzysztof Wilczyński <kwilczynski@kernel.org>

Thank you!

	Krzysztof