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qga: Fix undefined C behavior

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The QAPI struct GuestFileWhence has a comment about how we are
exploiting equivalent values between two different integer types
shared in a union. But C says behavior is undefined on assignments to
overlapping storage when the two types are not the same width, and
indeed, 'int64_t value' and 'enum QGASeek name' are very likely to be
different in width.  Utilize a temporary variable to fix things.

Reported-by: Peter Maydell <peter.maydell@linaro.org>
Fixes: 0b4b49387
Fixes: Coverity CID 1421990
Signed-off-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
This commit is contained in:
Eric Blake 2020-03-20 10:05:07 -05:00 • committed by Michael Roth
parent 807e2b6fce
commit a23f38a729
1 changed files with 7 additions and 2 deletions
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9
qga/commands.c
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@ -482,10 +482,15 @@ done:
* the guest's SEEK_ constants. */ * the guest's SEEK_ constants. */
int ga_parse_whence(GuestFileWhence *whence, Error **errp) int ga_parse_whence(GuestFileWhence *whence, Error **errp)
{ {
/* Exploit the fact that we picked values to match QGA_SEEK_*. */ /*
* Exploit the fact that we picked values to match QGA_SEEK_*;
* however, we have to use a temporary variable since the union
* members may have different size.
*/
if (whence->type == QTYPE_QSTRING) { if (whence->type == QTYPE_QSTRING) {
int value = whence->u.name;
whence->type = QTYPE_QNUM; whence->type = QTYPE_QNUM;
whence->u.value = whence->u.name; whence->u.value = value;
} }
switch (whence->u.value) { switch (whence->u.value) {
case QGA_SEEK_SET: case QGA_SEEK_SET: