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PCI: Return ~0 data on pciconfig_read() CAP_SYS_ADMIN failure

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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
e4585da22a ("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 e4585da22a,
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: e4585da22a ("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
This commit is contained in:
Krzysztof Wilczyński 2021-07-29 23:37:54 +00:00 committed by Bjorn Helgaas
parent b12d93e995
commit a8bd29bd49
1 changed files with 3 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
drivers/pci/syscall.c
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@ -22,8 +22,10 @@ SYSCALL_DEFINE5(pciconfig_read, unsigned long, bus, unsigned long, dfn,
long err;
int cfg_ret;
err = -EPERM;
dev = NULL;
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
goto error;
err = -ENODEV;
dev = pci_get_domain_bus_and_slot(0, bus, dfn);