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util: forbid freeing const pointers

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Now that we've finally fixed all the violators, it's time to
enforce that any pointer to a const object is never freed (it
is aliasing some other memory, where the non-const original
should be freed instead).  Alas, the code still needs a normal
vs. Coverity version, but at least we are still guaranteeing
that the macro call evaluates its argument exactly once.

I verified that we still get the following compiler warnings,
which in turn halts the build thanks to -Werror on gcc (hmm,
gcc 4.8.3's placement of the ^ for ?: type mismatch is a bit
off, but that's not our problem):

    int oops1 = 0;
    VIR_FREE(oops1);
    const char *oops2 = NULL;
    VIR_FREE(oops2);
    struct blah { int dummy; } oops3;
    VIR_FREE(oops3);

util/virauthconfig.c:159:35: error: pointer/integer type mismatch in conditional expression [-Werror]
     VIR_FREE(oops1);
                                   ^
util/virauthconfig.c:161:5: error: passing argument 1 of 'virFree' discards 'const' qualifier from pointer target type [-Werror]
     VIR_FREE(oops2);
     ^
In file included from util/virauthconfig.c:28:0:
util/viralloc.h:79:6: note: expected 'void *' but argument is of type 'const void *'
 void virFree(void *ptrptr) ATTRIBUTE_NONNULL(1);
      ^
util/virauthconfig.c:163:35: error: type mismatch in conditional expression
     VIR_FREE(oops3);
                                   ^

* src/util/viralloc.h (VIR_FREE): No longer cast away const.
* src/xenapi/xenapi_utils.c (xenSessionFree): Work around bogus
header.

Signed-off-by: Eric Blake <eblake@redhat.com>
This commit is contained in:
Eric Blake 2014-07-15 13:44:26 -06:00
parent 0b0c641b66
commit a0b5ace28c
2 changed files with 8 additions and 7 deletions
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11
src/util/viralloc.h
View File

@ -548,18 +548,17 @@ void virFree(void *ptrptr) ATTRIBUTE_NONNULL(1);
* This macro is safe to use on arguments with side effects.
*/
# if !STATIC_ANALYSIS
/* The ternary ensures that ptr is a pointer and not an integer type,
* while evaluating ptr only once. This gives us extra compiler
* safety when compiling under gcc. For now, we intentionally cast
* away const, since a number of callers safely pass const char *.
/* The ternary ensures that ptr is a non-const pointer and not an
* integer type, all while evaluating ptr only once. This gives us
* extra compiler safety when compiling under gcc.
*/
# define VIR_FREE(ptr) virFree((void *) (1 ? (const void *) &(ptr) : (ptr)))
# define VIR_FREE(ptr) virFree(1 ? (void *) &(ptr) : (ptr))
# else
/* The Coverity static analyzer considers the else path of the "?:" and
* flags the VIR_FREE() of the address of the address of memory as a
* RESOURCE_LEAK resulting in numerous false positives (eg, VIR_FREE(&ptr))
*/
# define VIR_FREE(ptr) virFree((void *) &(ptr))
# define VIR_FREE(ptr) virFree(&(ptr))
# endif
void virAllocTestInit(void);

4
src/xenapi/xenapi_utils.c
View File

@ -44,13 +44,15 @@ void
xenSessionFree(xen_session *session)
{
size_t i;
char *tmp;
if (session->error_description != NULL) {
for (i = 0; i < session->error_description_count; i++)
VIR_FREE(session->error_description[i]);
VIR_FREE(session->error_description);
}
/* The session_id member is type of 'const char *'. Sigh. */
VIR_FREE(session->session_id);
tmp = (char *)session->session_id;
VIR_FREE(tmp);
VIR_FREE(session);
}