[PATCH libdrm] xf86drm: fix valgrind warning in drmParsePciBusInfo

[Nicholas Miell]

>From 714d07f600db39498c87d7816f4dd3a7e6d9bbca Mon Sep 17 00:00:00 2001
From: Nicholas Miell <nmiell at gmail.com>
Date: Thu, 12 Jan 2017 15:43:07 -0800
Subject: [PATCH libdrm] xf86drm: fix valgrind warning in drmParsePciBusInfo

The current implementation reads (up to) 513 bytes, overwrites the 513th
byte with '\0' and then passes the buffer off to strstr() and sscanf()
without ever initializing the middle bytes. This causes valgrind
warnings and potentially fails to parse PCI_SLOT_NAME if the uevent is
unexpectedly large.

Rewrite it using getline() to fix the valgrind errors and future-proof
the function against uevent files larger than 513 bytes.

Signed-off-by: Nicholas Miell <nmiell at gmail.com>
---
 xf86drm.c | 34 +++++++++++++++++-----------------
 1 file changed, 17 insertions(+), 17 deletions(-)

diff --git a/xf86drm.c b/xf86drm.c
index b8b2cfe..33261ac 100644
--- a/xf86drm.c
+++ b/xf86drm.c
@@ -2919,31 +2919,31 @@ static int drmParsePciBusInfo(int maj, int min, drmPciBusInfoPtr info)
 {
 #ifdef __linux__
     char path[PATH_MAX + 1];
-    char data[512 + 1];
-    char *str;
+    FILE *uevent;
+    char *line = NULL;
+    size_t n = 0;
+    bool found = false;
     int domain, bus, dev, func;
-    int fd, ret;
 
     snprintf(path, PATH_MAX, "/sys/dev/char/%d:%d/device/uevent", maj, min);
-    fd = open(path, O_RDONLY);
-    if (fd < 0)
+    uevent = fopen(path, "r");
+    if (uevent == NULL)
         return -errno;
 
-    ret = read(fd, data, sizeof(data));
-    data[sizeof(data)-1] = '\0';
-    close(fd);
-    if (ret < 0)
-        return -errno;
+    while (getline(&line, &n, uevent) != -1) {
+        if (sscanf(line, "PCI_SLOT_NAME=%04x:%02x:%02x.%1u",
+                   &domain, &bus, &dev, &func) == 4)
+        {
+	        found = true;
+	        break;
+        }
+    }
+    free(line);
 
-#define TAG "PCI_SLOT_NAME="
-    str = strstr(data, TAG);
-    if (str == NULL)
-        return -EINVAL;
+    fclose(uevent);
 
-    if (sscanf(str, TAG "%04x:%02x:%02x.%1u",
-               &domain, &bus, &dev, &func) != 4)
+    if (!found)
         return -EINVAL;
-#undef TAG
 
     info->domain = domain;
     info->bus = bus;
-- 
2.9.3