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Date: Mon, 18 Oct 2021 18:14:53 +0200
From: Lukas Bulwahn <lukas.bulwahn@...il.com>
To: Steven Rostedt <rostedt@...dmis.org>, llvm@...ts.linux.dev,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Some potentially uninitialized values in pid_list_refill_irq()
Dear Steven,
Commit 8d6e90983ade ("tracing: Create a sparse bitmask for pid
filtering") in linux-next adds the new function pid_list_refill_irq().
For this function, 'make clang-analyzer' reports potentially
uninitialized values for lower and upper under certain branch
conditions, see the full report below.
As far as I understand the analyzer's report and the code at hand:
if lower_count is zero (and upper_count is not), then lower_next is
not assigned (because the while lower_count loop is not entered) and
lower is pointing to an address with an uninitialized value and hence,
the if (lower) conditional reads this uninitialized value.
Analogously for upper_count:
if upper_count is zero (and lower_count is not), then upper_count is
not assigned (because the while upper_count loop is not entered) and
upper is pointing to an address with an uninitialized value and hence,
the if (upper) conditional reads this uninitialized value.
I think this can be resolved by initializing upper and lower to point
to an address carrying a zero; but I really fight understanding the
whole pointer magic, you did :)
Let me know if clang-analyzer found something buggy here or if the
tool and I misunderstood the code; we are certainly interested.
Lukas
---
./kernel/trace/pid_list.c:377:6: warning: Branch condition evaluates
to a garbage value [clang-analyzer-core.uninitialized.Branch]
if (upper) {
^~~~~
./kernel/trace/pid_list.c:334:36: note: Left side of '&&' is false
struct trace_pid_list *pid_list = container_of(iwork, struct
trace_pid_list,
^
./include/linux/container_of.h:19:61: note: expanded from macro 'container_of'
BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) && \
^
./kernel/trace/pid_list.c:334:36: note: Taking false branch
struct trace_pid_list *pid_list = container_of(iwork, struct
trace_pid_list,
^
./include/linux/container_of.h:19:2: note: expanded from macro 'container_of'
BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) && \
^
./include/linux/build_bug.h:39:37: note: expanded from macro 'BUILD_BUG_ON_MSG'
#define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
^
./include/linux/compiler_types.h:329:2: note: expanded from macro
'compiletime_assert'
_compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
^
./include/linux/compiler_types.h:317:2: note: expanded from macro
'_compiletime_assert'
__compiletime_assert(condition, msg, prefix, suffix)
^
./include/linux/compiler_types.h:309:3: note: expanded from macro
'__compiletime_assert'
if (!(condition)) \
^
./kernel/trace/pid_list.c:334:36: note: Loop condition is false. Exiting loop
struct trace_pid_list *pid_list = container_of(iwork, struct
trace_pid_list,
^
./include/linux/container_of.h:19:2: note: expanded from macro 'container_of'
BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) && \
^
./include/linux/build_bug.h:39:37: note: expanded from macro 'BUILD_BUG_ON_MSG'
#define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
^
./include/linux/compiler_types.h:329:2: note: expanded from macro
'compiletime_assert'
_compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
^
./include/linux/compiler_types.h:317:2: note: expanded from macro
'_compiletime_assert'
__compiletime_assert(condition, msg, prefix, suffix)
^
./include/linux/compiler_types.h:307:2: note: expanded from macro
'__compiletime_assert'
do { \
^
./kernel/trace/pid_list.c:336:2: note: 'upper' declared without an initial value
union upper_chunk *upper;
^~~~~~~~~~~~~~~~~~~~~~~~
./kernel/trace/pid_list.c:351:6: note: Assuming 'upper_count' is > 0
if (upper_count <= 0 && lower_count <= 0)
^~~~~~~~~~~~~~~~
./kernel/trace/pid_list.c:351:23: note: Left side of '&&' is false
if (upper_count <= 0 && lower_count <= 0)
^
./kernel/trace/pid_list.c:354:2: note: Loop condition is true.
Entering loop body
while (upper_count-- > 0) {
^
./kernel/trace/pid_list.c:358:7: note: Assuming 'chunk' is null
if (!chunk)
^~~~~~
./kernel/trace/pid_list.c:358:3: note: Taking true branch
if (!chunk)
^
./kernel/trace/pid_list.c:359:4: note: Execution continues on line 365
break;
^
./kernel/trace/pid_list.c:365:9: note: Assuming the condition is false
while (lower_count-- > 0) {
^~~~~~~~~~~~~~~~~
./kernel/trace/pid_list.c:365:2: note: Loop condition is false.
Execution continues on line 376
while (lower_count-- > 0) {
^
./kernel/trace/pid_list.c:377:6: note: Branch condition evaluates to a
garbage value
if (upper) {
^~~~~
./kernel/trace/pid_list.c:382:6: warning: Branch condition evaluates
to a garbage value [clang-analyzer-core.uninitialized.Branch]
if (lower) {
^~~~~
./kernel/trace/pid_list.c:334:36: note: Left side of '&&' is false
struct trace_pid_list *pid_list = container_of(iwork, struct
trace_pid_list,
^
./include/linux/container_of.h:19:61: note: expanded from macro 'container_of'
BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) && \
^
./kernel/trace/pid_list.c:334:36: note: Taking false branch
struct trace_pid_list *pid_list = container_of(iwork, struct
trace_pid_list,
^
./include/linux/container_of.h:19:2: note: expanded from macro 'container_of'
BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) && \
^
./include/linux/build_bug.h:39:37: note: expanded from macro 'BUILD_BUG_ON_MSG'
#define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
^
./include/linux/compiler_types.h:329:2: note: expanded from macro
'compiletime_assert'
_compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
^
./include/linux/compiler_types.h:317:2: note: expanded from macro
'_compiletime_assert'
__compiletime_assert(condition, msg, prefix, suffix)
^
./include/linux/compiler_types.h:309:3: note: expanded from macro
'__compiletime_assert'
if (!(condition)) \
^
./kernel/trace/pid_list.c:334:36: note: Loop condition is false. Exiting loop
struct trace_pid_list *pid_list = container_of(iwork, struct
trace_pid_list,
^
./include/linux/container_of.h:19:2: note: expanded from macro 'container_of'
BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) && \
^
./include/linux/build_bug.h:39:37: note: expanded from macro 'BUILD_BUG_ON_MSG'
#define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
^
./include/linux/compiler_types.h:329:2: note: expanded from macro
'compiletime_assert'
_compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
^
./include/linux/compiler_types.h:317:2: note: expanded from macro
'_compiletime_assert'
__compiletime_assert(condition, msg, prefix, suffix)
^
./include/linux/compiler_types.h:307:2: note: expanded from macro
'__compiletime_assert'
do { \
^
./kernel/trace/pid_list.c:337:2: note: 'lower' declared without an initial value
union lower_chunk *lower;
^~~~~~~~~~~~~~~~~~~~~~~~
./kernel/trace/pid_list.c:351:6: note: Assuming 'upper_count' is > 0
if (upper_count <= 0 && lower_count <= 0)
^~~~~~~~~~~~~~~~
./kernel/trace/pid_list.c:351:23: note: Left side of '&&' is false
if (upper_count <= 0 && lower_count <= 0)
^
./kernel/trace/pid_list.c:354:2: note: Loop condition is true.
Entering loop body
while (upper_count-- > 0) {
^
./kernel/trace/pid_list.c:358:7: note: Assuming 'chunk' is non-null
if (!chunk)
^~~~~~
./kernel/trace/pid_list.c:358:3: note: Taking false branch
if (!chunk)
^
./kernel/trace/pid_list.c:354:9: note: Assuming the condition is false
while (upper_count-- > 0) {
^~~~~~~~~~~~~~~~~
./kernel/trace/pid_list.c:354:2: note: Loop condition is false.
Execution continues on line 365
while (upper_count-- > 0) {
^
./kernel/trace/pid_list.c:365:9: note: Assuming the condition is false
while (lower_count-- > 0) {
^~~~~~~~~~~~~~~~~
./kernel/trace/pid_list.c:365:2: note: Loop condition is false.
Execution continues on line 376
while (lower_count-- > 0) {
^
./kernel/trace/pid_list.c:377:6: note: 'upper' is non-null
if (upper) {
^~~~~
./kernel/trace/pid_list.c:377:2: note: Taking true branch
if (upper) {
^
./kernel/trace/pid_list.c:382:6: note: Branch condition evaluates to a
garbage value
if (lower) {
^~~~~
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