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@xxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Closes: https://syzkaller.appspot.com/bug?extid=c7604c9fdd7580cca4e0
> > Tested-by: syzbot+c7604c9fdd7580cca4e0@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Signed-off-by: Deepanshu Kartikey <kartikey406@xxxxxxxxx>
> > ---
> > 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.