From: Krzysztof Wilczyński kw@linux.com
commit a8bd29bd49c4156ea0ec5a97812333e2aeef44e7 upstream.
The pciconfig_read() syscall reads PCI configuration space using hardware-dependent config accessors.
If the read fails on PCI, most accessors don't return an error; they pretend the read was successful and got ~0 data from the device, so the syscall returns success with ~0 data in the buffer.
When the accessor does return an error, pciconfig_read() normally fills the user's buffer with ~0 and returns an error in errno. But after e4585da22ad0 ("pci syscall.c: Switch to refcounting API"), we don't fill the buffer with ~0 for the EPERM "user lacks CAP_SYS_ADMIN" error.
Userspace may rely on the ~0 data to detect errors, but after e4585da22ad0, that would not detect CAP_SYS_ADMIN errors.
Restore the original behaviour of filling the buffer with ~0 when the CAP_SYS_ADMIN check fails.
[bhelgaas: commit log, fold in Nathan's fix https://lore.kernel.org/r/20210803200836.500658-1-nathan@kernel.org] Fixes: e4585da22ad0 ("pci syscall.c: Switch to refcounting API") Link: https://lore.kernel.org/r/20210729233755.1509616-1-kw@linux.com Signed-off-by: Krzysztof Wilczyński kw@linux.com Signed-off-by: Bjorn Helgaas bhelgaas@google.com Cc: stable@vger.kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/pci/syscall.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
--- a/drivers/pci/syscall.c +++ b/drivers/pci/syscall.c @@ -23,8 +23,10 @@ SYSCALL_DEFINE5(pciconfig_read, unsigned long err; int cfg_ret;
+ err = -EPERM; + dev = NULL; if (!capable(CAP_SYS_ADMIN)) - return -EPERM; + goto error;
err = -ENODEV; dev = pci_get_bus_and_slot(bus, dfn);