This reverts commit 46bbe5c671e06f070428b9be142cc4ee5cedebac.
As commit 46bbe5c671e0 ("tracing: fix double free") said, the "double free" problem reported by clang static analyzer is:
In parse_var_defs() if there is a problem allocating var_defs.expr, the earlier var_defs.name is freed. This free is duplicated by free_var_defs() which frees the rest of the list.
However, if there is a problem allocating N-th var_defs.expr: + in parse_var_defs(), the freed 'earlier var_defs.name' is actually the N-th var_defs.name; + then in free_var_defs(), the names from 0th to (N-1)-th are freed;
IF ALLOCATING PROBLEM HAPPENED HERE!!! -+ \ | 0th 1th (N-1)-th N-th V +-------------+-------------+-----+-------------+----------- var_defs: | name | expr | name | expr | ... | name | expr | name | /// +-------------+-------------+-----+-------------+-----------
These two frees don't act on same name, so there was no "double free" problem before. Conversely, after that commit, we get a "memory leak" problem because the above "N-th var_defs.name" is not freed.
If enable CONFIG_DEBUG_KMEMLEAK and inject a fault at where the N-th var_defs.expr allocated, then execute on shell like: $ echo 'hist:key=call_site:val=$v1,$v2:v1=bytes_req,v2=bytes_alloc' > \ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
Then kmemleak reports: unreferenced object 0xffff8fb100ef3518 (size 8): comm "bash", pid 196, jiffies 4295681690 (age 28.538s) hex dump (first 8 bytes): 76 31 00 00 b1 8f ff ff v1...... backtrace: [<0000000038fe4895>] kstrdup+0x2d/0x60 [<00000000c99c049a>] event_hist_trigger_parse+0x206f/0x20e0 [<00000000ae70d2cc>] trigger_process_regex+0xc0/0x110 [<0000000066737a4c>] event_trigger_write+0x75/0xd0 [<000000007341e40c>] vfs_write+0xbb/0x2a0 [<0000000087fde4c2>] ksys_write+0x59/0xd0 [<00000000581e9cdf>] do_syscall_64+0x3a/0x80 [<00000000cf3b065c>] entry_SYSCALL_64_after_hwframe+0x46/0xb0
Cc: stable@vger.kernel.org Fixes: 46bbe5c671e0 ("tracing: fix double free") Reported-by: Hulk Robot hulkci@huawei.com Signed-off-by: Zheng Yejian zhengyejian1@huawei.com --- kernel/trace/trace_events_hist.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c index 48e82e141d54..2784951e0fc8 100644 --- a/kernel/trace/trace_events_hist.c +++ b/kernel/trace/trace_events_hist.c @@ -4430,6 +4430,7 @@ static int parse_var_defs(struct hist_trigger_data *hist_data)
s = kstrdup(field_str, GFP_KERNEL); if (!s) { + kfree(hist_data->attrs->var_defs.name[n_vars]); ret = -ENOMEM; goto free; }
On Thu, 30 Jun 2022 09:31:37 +0800 Zheng Yejian zhengyejian1@huawei.com wrote:
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c index 48e82e141d54..2784951e0fc8 100644 --- a/kernel/trace/trace_events_hist.c +++ b/kernel/trace/trace_events_hist.c @@ -4430,6 +4430,7 @@ static int parse_var_defs(struct hist_trigger_data *hist_data) s = kstrdup(field_str, GFP_KERNEL); if (!s) {
kfree(hist_data->attrs->var_defs.name[n_vars]);
Instead of doing just a revert, can we also add, for safety:
hist_data->attrs->var_defs.name[n_vars] = NULL;
Thanks,
-- Steve
ret = -ENOMEM; goto free; }
This reverts commit 46bbe5c671e06f070428b9be142cc4ee5cedebac.
As commit 46bbe5c671e0 ("tracing: fix double free") said, the "double free" problem reported by clang static analyzer is:
In parse_var_defs() if there is a problem allocating var_defs.expr, the earlier var_defs.name is freed. This free is duplicated by free_var_defs() which frees the rest of the list.
However, if there is a problem allocating N-th var_defs.expr: + in parse_var_defs(), the freed 'earlier var_defs.name' is actually the N-th var_defs.name; + then in free_var_defs(), the names from 0th to (N-1)-th are freed;
IF ALLOCATING PROBLEM HAPPENED HERE!!! -+ \ | 0th 1th (N-1)-th N-th V +-------------+-------------+-----+-------------+----------- var_defs: | name | expr | name | expr | ... | name | expr | name | /// +-------------+-------------+-----+-------------+-----------
These two frees don't act on same name, so there was no "double free" problem before. Conversely, after that commit, we get a "memory leak" problem because the above "N-th var_defs.name" is not freed.
If enable CONFIG_DEBUG_KMEMLEAK and inject a fault at where the N-th var_defs.expr allocated, then execute on shell like: $ echo 'hist:key=call_site:val=$v1,$v2:v1=bytes_req,v2=bytes_alloc' > \ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
Then kmemleak reports: unreferenced object 0xffff8fb100ef3518 (size 8): comm "bash", pid 196, jiffies 4295681690 (age 28.538s) hex dump (first 8 bytes): 76 31 00 00 b1 8f ff ff v1...... backtrace: [<0000000038fe4895>] kstrdup+0x2d/0x60 [<00000000c99c049a>] event_hist_trigger_parse+0x206f/0x20e0 [<00000000ae70d2cc>] trigger_process_regex+0xc0/0x110 [<0000000066737a4c>] event_trigger_write+0x75/0xd0 [<000000007341e40c>] vfs_write+0xbb/0x2a0 [<0000000087fde4c2>] ksys_write+0x59/0xd0 [<00000000581e9cdf>] do_syscall_64+0x3a/0x80 [<00000000cf3b065c>] entry_SYSCALL_64_after_hwframe+0x46/0xb0
Cc: stable@vger.kernel.org Fixes: 46bbe5c671e0 ("tracing: fix double free") Reported-by: Hulk Robot hulkci@huawei.com Suggested-by: Steven Rostedt rostedt@goodmis.org Signed-off-by: Zheng Yejian zhengyejian1@huawei.com --- kernel/trace/trace_events_hist.c | 2 ++ 1 file changed, 2 insertions(+)
Changes since v1: - Assign 'NULL' after 'kfree' for safety as suggested by Steven - Rename commit title and add Suggested-by tag
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c index 48e82e141d54..e87a46794079 100644 --- a/kernel/trace/trace_events_hist.c +++ b/kernel/trace/trace_events_hist.c @@ -4430,6 +4430,8 @@ static int parse_var_defs(struct hist_trigger_data *hist_data)
s = kstrdup(field_str, GFP_KERNEL); if (!s) { + kfree(hist_data->attrs->var_defs.name[n_vars]); + hist_data->attrs->var_defs.name[n_vars] = NULL; ret = -ENOMEM; goto free; }
Hi Yejian,
On 7/10/2022 8:47 PM, Zheng Yejian wrote:
This reverts commit 46bbe5c671e06f070428b9be142cc4ee5cedebac.
As commit 46bbe5c671e0 ("tracing: fix double free") said, the "double free" problem reported by clang static analyzer is:
In parse_var_defs() if there is a problem allocating var_defs.expr, the earlier var_defs.name is freed. This free is duplicated by free_var_defs() which frees the rest of the list.
However, if there is a problem allocating N-th var_defs.expr:
in parse_var_defs(), the freed 'earlier var_defs.name' is actually the N-th var_defs.name;
then in free_var_defs(), the names from 0th to (N-1)-th are freed;
IF ALLOCATING PROBLEM HAPPENED HERE!!! -+ \ | 0th 1th (N-1)-th N-th V +-------------+-------------+-----+-------------+-----------var_defs: | name | expr | name | expr | ... | name | expr | name | /// +-------------+-------------+-----+-------------+-----------
These two frees don't act on same name, so there was no "double free" problem before. Conversely, after that commit, we get a "memory leak" problem because the above "N-th var_defs.name" is not freed.
Good catch, thanks for fixing it.
So I'm wondering if this means that that the original unnecessary bugfix was based on a bug in the clang static analyzer or if that would just be considered a false positive...
Reviewed-by: Tom Zanussi tom.zanussi@linux.intel.com
Tom
If enable CONFIG_DEBUG_KMEMLEAK and inject a fault at where the N-th var_defs.expr allocated, then execute on shell like: $ echo 'hist:key=call_site:val=$v1,$v2:v1=bytes_req,v2=bytes_alloc' > \ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
Then kmemleak reports: unreferenced object 0xffff8fb100ef3518 (size 8): comm "bash", pid 196, jiffies 4295681690 (age 28.538s) hex dump (first 8 bytes): 76 31 00 00 b1 8f ff ff v1...... backtrace: [<0000000038fe4895>] kstrdup+0x2d/0x60 [<00000000c99c049a>] event_hist_trigger_parse+0x206f/0x20e0 [<00000000ae70d2cc>] trigger_process_regex+0xc0/0x110 [<0000000066737a4c>] event_trigger_write+0x75/0xd0 [<000000007341e40c>] vfs_write+0xbb/0x2a0 [<0000000087fde4c2>] ksys_write+0x59/0xd0 [<00000000581e9cdf>] do_syscall_64+0x3a/0x80 [<00000000cf3b065c>] entry_SYSCALL_64_after_hwframe+0x46/0xb0
Cc: stable@vger.kernel.org Fixes: 46bbe5c671e0 ("tracing: fix double free") Reported-by: Hulk Robot hulkci@huawei.com Suggested-by: Steven Rostedt rostedt@goodmis.org Signed-off-by: Zheng Yejian zhengyejian1@huawei.com
kernel/trace/trace_events_hist.c | 2 ++ 1 file changed, 2 insertions(+)
Changes since v1:
- Assign 'NULL' after 'kfree' for safety as suggested by Steven
- Rename commit title and add Suggested-by tag
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c index 48e82e141d54..e87a46794079 100644 --- a/kernel/trace/trace_events_hist.c +++ b/kernel/trace/trace_events_hist.c @@ -4430,6 +4430,8 @@ static int parse_var_defs(struct hist_trigger_data *hist_data) s = kstrdup(field_str, GFP_KERNEL); if (!s) {
kfree(hist_data->attrs->var_defs.name[n_vars]);hist_data->attrs->var_defs.name[n_vars] = NULL; ret = -ENOMEM; goto free; }
On Mon, 11 Jul 2022 09:27:44 -0500 "Zanussi, Tom" tom.zanussi@linux.intel.com wrote:
So I'm wondering if this means that that the original unnecessary bugfix was based on a bug in the clang static analyzer or if that would just be considered a false positive...
Good question. I'd like to know this, as if it is the case, I want to report that in my pull request to Linus.
-- Steve
On Mon, 11 Jul 2022 11:52:11 -0400 Steven Rostedt rostedt@goodmis.org wrote:
On Mon, 11 Jul 2022 09:27:44 -0500 "Zanussi, Tom" tom.zanussi@linux.intel.com wrote:
So I'm wondering if this means that that the original unnecessary bugfix was based on a bug in the clang static analyzer or if that would just be considered a false positive...
Good question. I'd like to know this, as if it is the case, I want to report that in my pull request to Linus.
-- Steve
I didn't use clang static analyzer before, but from its home page, 'False Positives' seems to exist, see https://clang-analyzer.llvm.org/: > Static analysis is not perfect. It can falsely flag bugs in a program > where the code behaves correctly. Because some code checks require more > analysis precision than others, the frequency of false positives can > vary widely between different checks. Our long-term goal is to have the > analyzer have a low false positive rate for most code on all checks.
So I try the clang-14 which comes from https://github.com/llvm/llvm-project/releases/tag/llvmorg-14.0.0, then execute like: $ scan-build make -j16
Then I take a rough look at following warnings related to 'trace_events_hist.c' (serial number is manually added, no double free warning, maybe due to clang version): 1. kernel/trace/trace_events_hist.c:1540:6: warning: Branch condition evaluates to a garbage value [core.uninitialized.Branch] if (!attrs->keys_str) { ^~~~~~~~~~~~~~~~ 2. kernel/trace/trace_events_hist.c:1580:9: warning: Array access (via field 'field_var_str') results in a null pointer dereference [core.NullDereference] kfree(elt_data->field_var_str[i]); ^~~~~~~~~~~~~~~~~~~~~~~~~~ 3. kernel/trace/trace_events_hist.c:1898:3: warning: 1st function call argument is an uninitialized value [core.CallAndMessage] destroy_hist_field(hist_field->operands[i], level + 1); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 4. kernel/trace/trace_events_hist.c:2095:2: warning: 1st function call argument is an uninitialized value [core.CallAndMessage] kfree(ref_field->system); ^~~~~~~~~~~~~~~~~~~~~~~~ 5. kernel/trace/trace_events_hist.c:2099:2: warning: 1st function call argument is an uninitialized value [core.CallAndMessage] kfree(ref_field->name); ^~~~~~~~~~~~~~~~~~~~~~ 6. kernel/trace/trace_events_hist.c:2158:4: warning: Potential leak of memory pointed to by 'ref_field' [unix.Malloc] return NULL;
Since I'm not very familiar with trace_events_hist.c, I roughly conclude that: 1. warning 1/3/6 are plausible but false-positive; 2. warning 2/4/5 seems positive although they don't cause practical problems because elt_data->field_var_str[i] / ref_field->system / ref_field->name can be 'NULL' on 'kfree'. Do we need to explicitly check 'NULL' there?
On Tue, 12 Jul 2022 19:48:44 +0800 Zheng Yejian zhengyejian1@huawei.com wrote:
Since I'm not very familiar with trace_events_hist.c, I roughly conclude that:
- warning 1/3/6 are plausible but false-positive;
- warning 2/4/5 seems positive although they don't cause practical problems because
elt_data->field_var_str[i] / ref_field->system / ref_field->name can be 'NULL' on 'kfree'. Do we need to explicitly check 'NULL' there?
It's confusing code. Both Tom and I missed it as well.
-- Steve
linux-stable-mirror@lists.linaro.org
-
Steven Rostedt -
Zanussi, Tom -
Zheng Yejian