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Buffer overflow in drivers/xen/sys-hypervisor.c

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The build id returned by HYPERVISOR_xen_version(XENVER_build_id) is
neither NUL terminated nor a string.

The first causes a buffer overflow as sprintf in buildid_show will
read and copy till it finds a NUL.

00000000  f4 91 51 f4 dd 38 9e 9d  65 47 52 eb 10 71 db 50  |..Q..8..eGR..q.P|
00000010  b9 a8 01 42 6f 2e 32                              |...Bo.2|
00000017

So use a memcpy instead of sprintf to have the correct value:

00000000  f4 91 51 f4 dd 00 9e 9d  65 47 52 eb 10 71 db 50  |..Q.....eGR..q.P|
00000010  b9 a8 01 42                                       |...B|
00000014

(the above have a hack to embed a zero inside and check it's
returned correctly).

This is XSA-485 / CVE-2026-31786

Fixes: 84b7625728 ("xen: add sysfs node for hypervisor build id")
Signed-off-by: Frediano Ziglio <frediano.ziglio@citrix.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
This commit is contained in:
Juergen Gross 2026-03-27 14:13:38 +01:00
parent 2e68039281
commit 27fdbab422
1 changed files with 6 additions and 2 deletions
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8
drivers/xen/sys-hypervisor.c
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@ -366,6 +366,8 @@ static ssize_t buildid_show(struct hyp_sysfs_attr *attr, char *buffer)
ret = sprintf(buffer, "<denied>");
return ret;
}
if (ret > PAGE_SIZE)
return -ENOSPC;
buildid = kmalloc(sizeof(*buildid) + ret, GFP_KERNEL);
if (!buildid)
@ -373,8 +375,10 @@ static ssize_t buildid_show(struct hyp_sysfs_attr *attr, char *buffer)
buildid->len = ret;
ret = HYPERVISOR_xen_version(XENVER_build_id, buildid);
if (ret > 0)
ret = sprintf(buffer, "%s", buildid->buf);
if (ret > 0) {
/* Build id is binary, not a string. */
memcpy(buffer, buildid->buf, ret);
}
kfree(buildid);
return ret;