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From 7bb8b4580b19f1d48e9beb201387d6c321b3ae7b Mon Sep 17 00:00:00 2001
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From: Jan Synacek <jsynacek@redhat.com>
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Date: Tue, 2 Oct 2018 16:07:00 +0200
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Subject: [PATCH] detect-virt: do not try to read all of /proc/cpuinfo
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Quoting #10074:
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> detect_vm_uml() reads /proc/cpuinfo with read_full_file()
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> read_full_file() has a file max limit size of READ_FULL_BYTES_MAX=(4U*1024U*1024U)
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> Unfortunately, the size of my /proc/cpuinfo is bigger, approximately:
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> echo $(( 4* $(cat /proc/cpuinfo | wc -c)))
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> 9918072
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> This causes read_full_file() to fail and the Condition test fallout.
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Let's just read line by line until we find an intersting line. This also
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helps if not running under UML, because we avoid reading as much data.
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(cherry picked from commit 6058516a14ada1748313af6783f5b4e7e3006654)
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Resolves: #1631531
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---
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 src/shared/virt.c | 40 ++++++++++++++++++++++++++++++++--------
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 1 file changed, 32 insertions(+), 8 deletions(-)
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diff --git a/src/shared/virt.c b/src/shared/virt.c
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index 55a6ca90fb..e6362f6645 100644
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--- a/src/shared/virt.c
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+++ b/src/shared/virt.c
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@@ -185,7 +185,8 @@ static int detect_vm_dmi(const char **_id) {
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 /* Returns a short identifier for the various VM implementations */
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 int detect_vm(const char **id) {
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-        _cleanup_free_ char *domcap = NULL, *cpuinfo_contents = NULL;
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+        _cleanup_free_ char *domcap = NULL;
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+        _cleanup_fclose_ FILE *f = NULL;
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         static thread_local int cached_found = -1;
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         static thread_local const char *cached_id = NULL;
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         const char *_id = NULL;
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@@ -252,13 +253,36 @@ int detect_vm(const char **id) {
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         }
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         /* Detect User-Mode Linux by reading /proc/cpuinfo */
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-        r = read_full_file("/proc/cpuinfo", &cpuinfo_contents, NULL);
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-        if (r < 0)
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-                return r;
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-        if (strstr(cpuinfo_contents, "\nvendor_id\t: User Mode Linux\n")) {
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-                _id = "uml";
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-                r = 1;
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-                goto finish;
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+        f = fopen("/proc/cpuinfo", "re");
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+        if (!f) {
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+                if (errno == ENOENT) {
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+                        log_debug("/proc/cpuinfo not found, assuming no UML virtualization.");
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+                        r = 0;
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+                        goto finish;
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+                }
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+                return -errno;
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+        }
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+        for (;;) {
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+                _cleanup_free_ char *line = NULL;
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+                const char *t;
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+
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+                r = read_line(f, LONG_LINE_MAX, &line);
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+                if (r < 0)
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+                        return r;
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+                if (r == 0)
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+                        break;
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+
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+                t = startswith(line, "vendor_id\t: ");
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+                if (t) {
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+                        if (startswith(t, "User Mode Linux")) {
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+                                log_debug("UML virtualization found in /proc/cpuinfo");
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+                                _id = "uml";
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+                                r = 1;
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+                                goto finish;
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+                        }
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+
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+                        break;
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+                }
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         }
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 #if defined(__s390__)