udev/net_id: Only read the first 64 bytes of PCI config space

The original code used fread(), which on some libc implementions
(ie glibc 2.17) would pre-read a full 4K (PAGE_SIZE) of the
PCI config space, when only 64 bytes were requested.

I have recently come across PCIe hardware which responds with
Completion Timeouts when accesses above 256 bytes are attempted.

This can cause server systems with GHES/AEPI support to cause
and immediate kernel panic due to the failed PCI transaction.

This change replaces the buffered fread() with an explict
unbuffered read() of 64 bytes, which corrects this issue by
only reading the guaranteed first 64 bytes of PCIe config space.

1 files changed, 5 insertions, 4 deletions

diff --git a/src/udev/udev-builtin-net_id.c b/src/udev/udev-builtin-net_id.c
index 78aef206b2..448920507a 100644
--- a/src/udev/udev-builtin-net_id.c
+++ b/src/udev/udev-builtin-net_id.c
@@ -91,6 +91,7 @@
 #include <stdlib.h>
 #include <stdarg.h>
 #include <unistd.h>
+#include <fcntl.h>
 #include <string.h>
 #include <errno.h>
 #include <net/if.h>
@@ -166,15 +167,15 @@ static int dev_pci_onboard(struct udev_device *dev, struct netnames *names) {
 
 /* read the 256 bytes PCI configuration space to check the multi-function bit */
 static bool is_pci_multifunction(struct udev_device *dev) {
-        _cleanup_fclose_ FILE *f = NULL;
+        _cleanup_close_ int fd = -1;
         const char *filename;
         uint8_t config[64];
 
         filename = strjoina(udev_device_get_syspath(dev), "/config");
-        f = fopen(filename, "re");
-        if (!f)
+        fd = open(filename, O_RDONLY | O_CLOEXEC);
+        if (fd < 0)
                 return false;
-        if (fread(&config, sizeof(config), 1, f) != 1)
+        if (read(fd, &config, sizeof(config)) != sizeof(config))
                 return false;
 
         /* bit 0-6 header type, bit 7 multi/single function device */