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Re: [PATCH-for-5.0] qga-posix: Avoid crashing process when failing to al

From: Philippe Mathieu-Daudé
Subject: Re: [PATCH-for-5.0] qga-posix: Avoid crashing process when failing to allocate memory
Date: Wed, 25 Mar 2020 13:10:11 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0

On 3/25/20 7:19 AM, Dietmar Maurer wrote:
but error_setg() also calls malloc, so this does not help at all?

IIUC the problem, you can send a QMP command to ask to read let's say 3GB of a file, and QEMU crashes. But this doesn't mean there the .heap is empty, there is probably few bytes still available, enough to respond with an error message.

On March 24, 2020 8:48 PM Philippe Mathieu-Daudé <address@hidden> wrote:

Similarly to commit 807e2b6fce0 for Windows, kindly return a
QMP error message instead of crashing the whole process.

Cc: address@hidden
Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1594054
Reported-by: Fakhri Zulkifli <address@hidden>
Signed-off-by: Philippe Mathieu-Daudé <address@hidden>
  qga/commands-posix.c | 8 +++++++-
  1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/qga/commands-posix.c b/qga/commands-posix.c
index 93474ff770..8f127788e6 100644
--- a/qga/commands-posix.c
+++ b/qga/commands-posix.c
@@ -493,7 +493,13 @@ struct GuestFileRead *qmp_guest_file_read(int64_t handle, 
bool has_count,
          gfh->state = RW_STATE_NEW;
- buf = g_malloc0(count+1);
+    buf = g_try_malloc0(count + 1);
+    if (!buf) {
+        error_setg(errp,
+                   "failed to allocate sufficient memory "
+                   "to complete the requested service");
+        return NULL;
+    }
      read_count = fread(buf, 1, count, fh);
      if (ferror(fh)) {
          error_setg_errno(errp, errno, "failed to read file");

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