[PATCH] libxl: don't segfault when creating domain with invalid pvusb device

[PATCH] libxl: don't segfault when creating domain with invalid pvusb device

[Juergen Gross]

Creating a domain with an invalid controller specification for a pvusb
device will currently segfault.

Avoid this by bailing out early in case of a mandatory xenstore path
not existing.

Signed-of-by: Juergen Gross <jgross@suse.com>
---
This patch is a backport candidate for 4.8
---
 tools/libxl/libxl_usb.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/tools/libxl/libxl_usb.c b/tools/libxl/libxl_usb.c
index ea7a2ab..b235507 100644
--- a/tools/libxl/libxl_usb.c
+++ b/tools/libxl/libxl_usb.c
@@ -651,12 +651,13 @@ int libxl_device_usbctrl_getinfo(libxl_ctx *ctx, uint32_t domid,
 
     usbctrlinfo->devid = usbctrl->devid;
 
-#define READ_SUBPATH(path, subpath) ({                                  \
-        rc = libxl__xs_read_checked(gc, XBT_NULL,                       \
-                                    GCSPRINTF("%s/" subpath, path),     \
-                                    &tmp);                              \
-        if (rc) goto out;                                               \
-        (char *)tmp;                                                    \
+#define READ_SUBPATH(path, subpath) ({                                      \
+        tmp = libxl__xs_read(gc, XBT_NULL, GCSPRINTF("%s/" subpath, path)); \
+        if (!tmp) {                                                         \
+            rc = ERROR_FAIL;                                                \
+            goto out;                                                       \
+        }                                                                   \
+        (char *)tmp;                                                        \
     })
 
 #define READ_SUBPATH_INT(path, subpath) ({                              \
-- 
2.10.2


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Re: [PATCH] libxl: don't segfault when creating domain with invalid pvusb device

[Ian Jackson]

Juergen Gross writes ("[PATCH] libxl: don't segfault when creating domain with invalid pvusb device"):
> Creating a domain with an invalid controller specification for a pvusb
> device will currently segfault.
> 
> Avoid this by bailing out early in case of a mandatory xenstore path
> not existing.

This should be done by adding a test of tmp for NULL.  libxl__xs_read
does no logging so is not really an improvement.

If you felt like inventing libxl__xs_read_must or something (maybe Wei
has a suggestion for a better name) that calls ENOENT a failure
instead, I'd be happy with that.

Thanks,
Ian.

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Re: [PATCH] libxl: don't segfault when creating domain with invalid pvusb device

[Juergen Gross]

On 07/02/17 19:36, Ian Jackson wrote:
> Juergen Gross writes ("[PATCH] libxl: don't segfault when creating domain with invalid pvusb device"):
>> Creating a domain with an invalid controller specification for a pvusb
>> device will currently segfault.
>>
>> Avoid this by bailing out early in case of a mandatory xenstore path
>> not existing.
> 
> This should be done by adding a test of tmp for NULL.  libxl__xs_read
> does no logging so is not really an improvement.
> 
> If you felt like inventing libxl__xs_read_must or something (maybe Wei
> has a suggestion for a better name) that calls ENOENT a failure
> instead, I'd be happy with that.

Okay. I think I'll name it libxl__xs_read_mandatory().


Juergen


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