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[23/99] console: Avoid segfault in screendump

Message ID 20180723201748.25573-24-mdroth@linux.vnet.ibm.com (mailing list archive)
State New, archived
Headers show
Series Patch Round-up for stable 2.12.1, freeze on 2018-07-30 | expand

Commit Message

Michael Roth July 23, 2018, 8:16 p.m. UTC 
From: Michal Privoznik <mprivozn@redhat.com>

After f771c5440e04626f1 it is possible to select device and
head which to take screendump from. And even though we check if
provided head number falls within range, it may still happen that
the console has no surface yet leading to SIGSEGV:

  qemu.git $ ./x86_64-softmmu/qemu-system-x86_64 \
    -qmp stdio \
    -device virtio-vga,id=video0,max_outputs=4

  {"execute":"qmp_capabilities"}
  {"execute":"screendump", "arguments":{"filename":"/tmp/screen.ppm", "device":"video0", "head":1}}
  Segmentation fault

 #0  0x00005628249dda88 in ppm_save (filename=0x56282826cbc0 "/tmp/screen.ppm", ds=0x0, errp=0x7fff52a6fae0) at ui/console.c:304
 #1  0x00005628249ddd9b in qmp_screendump (filename=0x56282826cbc0 "/tmp/screen.ppm", has_device=true, device=0x5628276902d0 "video0", has_head=true, head=1, errp=0x7fff52a6fae0) at ui/console.c:375
 #2  0x00005628247740df in qmp_marshal_screendump (args=0x562828265e00, ret=0x7fff52a6fb68, errp=0x7fff52a6fb60) at qapi/qapi-commands-ui.c:110

Here, @ds from frame #0 (or @surface from frame #1) is
dereferenced at the very beginning of ppm_save(). And because
it's NULL crash happens.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-id: cb05bb1909daa6ba62145c0194aafa05a14ed3d1.1526569138.git.mprivozn@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
(cherry picked from commit 08d9864fa4e0c616e076ca8b225d39a7ecb189af)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
---
 ui/console.c | 5 +++++
 1 file changed, 5 insertions(+)
diff mbox series

Patch

diff --git a/ui/console.c b/ui/console.c
index 3fb2f4e09f..476bf901a4 100644
--- a/ui/console.c
+++ b/ui/console.c
@@ -370,6 +370,11 @@  void qmp_screendump(const char *filename, bool has_device, const char *device,
 
     graphic_hw_update(con);
     surface = qemu_console_surface(con);
+    if (!surface) {
+        error_setg(errp, "no surface");
+        return;
+    }
+
     ppm_save(filename, surface, errp);
 }