Michael Hudson-Doyle created ZOOKEEPER-3954:
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Summary: use of uninitialized data in
zookeeper-client/zookeeper-client-c/src/zookeeper.c:free_auth_completion
Key: ZOOKEEPER-3954
URL: https://issues.apache.org/jira/browse/ZOOKEEPER-3954
Project: ZooKeeper
Issue Type: Bug
Components: c client
Affects Versions: 3.6.2
Reporter: Michael Hudson-Doyle
When compiled with {{-O3}} and {{gcc-10}} (which is the default for Ubuntu on
ppc64el), compilation fails like this:
{code:shell}
/bin/bash ./libtool -tag=CC --mode=compile gcc -DHAVE_CONFIG_H -I. -I./include
-I./tests -I./generated -Wdate-time -D_FORTIFY_SOURCE=2 -Wall -Werror -g -O3
-fdebug-prefix-map=/<<PKGBUILDDIR>>=. -fstack-protector-strong -Wformat
-Werror=format-security -MT zookeeper.lo -MD -MP -MF .deps/zookeeper.Tpo -c -o
zookeeper.lo `test -f 'src/zookeeper.c' || echo './'`src/zookeeper.c libtool:
compile: gcc -DHAVE_CONFIG_H -I. -I./include -I./tests -I./generated
-Wdate-time -D_FORTIFY_SOURCE=2 -Wall -Werror -g -O3
-fdebug-prefix-map=/<<PKGBUILDDIR>>=. -fstack-protector-strong -Wformat
-Werror=format-security -MT zookeeper.lo -MD -MP -MF .deps/zookeeper.Tpo -c
src/zookeeper.c -fPIC -DPIC -o .libs/zookeeper.o src/zookeeper.c: In function
'free_completions': src/zookeeper.c:284:9: error: 'a_list.next' may be used
uninitialized in this function [-Werror=maybe-uninitialized] 284 | tmp =
a_list>next; | ~~~^~~~~~~~~~~~~ cc1: all warnings being treated as errors{code}
What's happening here is that free_auth_completions is being inlined into
free_completions, and this lets gcc see that members of a_list are being
accessed without initialization. I don't know anything like enough about this
code to see if this is a bug in code paths that are actually taken but at a
glance it's certainly not obviously impossible: if the two if conditions at the
top level of free_completions evaluate false, the function effectively looks
like this:
{code:c}
void free_completions(zhandle_t *zh,int callCompletion,int reason)
{
auth_completion_list_t a_list;
free_auth_completion(&a_list);
}
{code}
so it's pretty clear that a_list is backed by uninitialized stack memory.
Explicitly initializing the variable with "a_list = {NULL, NULL, NULL}" makes
the warning go away.
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