[for-linus][PATCH 1/6] tracing/histograms: Fix memory leak problem

From: Steven Rostedt
Date: Tue Jul 12 2022 - 16:40:24 EST

From: Zheng Yejian <zhengyejian1@xxxxxxxxxx>

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;

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' > \

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......
[<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

Link: https://lkml.kernel.org/r/20220711014731.69520-1-zhengyejian1@xxxxxxxxxx

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 46bbe5c671e0 ("tracing: fix double free")
Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
Suggested-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Reviewed-by: Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx>
Signed-off-by: Zheng Yejian <zhengyejian1@xxxxxxxxxx>
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
kernel/trace/trace_events_hist.c | 2 ++
1 file changed, 2 insertions(+)

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;