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libsepol: silence potential NULL pointer dereference warning

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When find_avtab_node() is called with key->specified & AVTAB_XPERMS and
xperms=NULL, xperms is being dereferenced. This is detected as a
"NULL pointer dereference issue" by static analyzers.

Even though it does not make much sense to call find_avtab_node() in a
way which triggers the NULL pointer dereference issue, static analyzers
have a hard time with calls such as:

    node = find_avtab_node(handle, avtab, &avkey, cond, NULL);

... where xperms=NULL.

So, make the function report an error instead of crashing.

Here is an example of report from clang's static analyzer:
https://558-118970575-gh.circle-artifacts.com/0/output-scan-build/2020-10-02-065849-6375-1/report-d86a57.html#EndPath

Signed-off-by: Nicolas Iooss <nicolas.iooss@m4x.org>
This commit is contained in:
Nicolas Iooss 2020-10-03 15:56:58 +02:00
parent 64387cb373
commit c97d63c6b4
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GPG key ID: C191415F340DAAA0
1 changed files with 15 additions and 10 deletions
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25
libsepol/src/expand.c
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@ -1570,17 +1570,22 @@ static avtab_ptr_t find_avtab_node(sepol_handle_t * handle,
/* AVTAB_XPERMS entries are not necessarily unique */
if (key->specified & AVTAB_XPERMS) {
node = avtab_search_node(avtab, key);
while (node) {
if ((node->datum.xperms->specified == xperms->specified) &&
(node->datum.xperms->driver == xperms->driver)) {
match = 1;
break;
}
node = avtab_search_node_next(node, key->specified);
}
if (!match)
if (xperms == NULL) {
ERR(handle, "searching xperms NULL");
node = NULL;
} else {
node = avtab_search_node(avtab, key);
while (node) {
if ((node->datum.xperms->specified == xperms->specified) &&
(node->datum.xperms->driver == xperms->driver)) {
match = 1;
break;
}
node = avtab_search_node_next(node, key->specified);
}
if (!match)
node = NULL;
}
} else {
node = avtab_search_node(avtab, key);
}