[PATCH 6.1 166/197] tracing: Inform kmemleak of saved_cmdlines allocation

Greg Kroah-Hartman
2024-02-20T21:07:32Z

From: Steven Rostedt (Google) <rostedt@goodmis.org>

commit 2394ac4145ea91b92271e675a09af2a9ea6840b7 upstream.

The allocation of the struct saved_cmdlines_buffer structure changed from:

s = kmalloc(sizeof(*s), GFP_KERNEL);
s->saved_cmdlines = kmalloc_array(TASK_COMM_LEN, val, GFP_KERNEL);

to:

orig_size = sizeof(*s) + val * TASK_COMM_LEN;
order = get_order(orig_size);
size = 1 << (order + PAGE_SHIFT);
page = alloc_pages(GFP_KERNEL, order);
if (!page)
return NULL;

s = page_address(page);
memset(s, 0, sizeof(*s));

s->saved_cmdlines = kmalloc_array(TASK_COMM_LEN, val, GFP_KERNEL);

Where that s->saved_cmdlines allocation looks to be a dangling allocation
to kmemleak. That's because kmemleak only keeps track of kmalloc()
allocations. For allocations that use page_alloc() directly, the kmemleak
needs to be explicitly informed about it.

Add kmemleak_alloc() and kmemleak_free() around the page allocation so
that it doesn't give the following false positive:

unreferenced object 0xffff8881010c8000 (size 32760):
comm "swapper", pid 0, jiffies 4294667296
hex dump (first 32 bytes):
ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ................
ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ................
backtrace (crc ae6ec1b9):
[<ffffffff86722405>] kmemleak_alloc+0x45/0x80
[<ffffffff8414028d>] __kmalloc_large_node+0x10d/0x190
[<ffffffff84146ab1>] __kmalloc+0x3b1/0x4c0
[<ffffffff83ed7103>] allocate_cmdlines_buffer+0x113/0x230
[<ffffffff88649c34>] tracer_alloc_buffers.isra.0+0x124/0x460
[<ffffffff8864a174>] early_trace_init+0x14/0xa0
[<ffffffff885dd5ae>] start_kernel+0x12e/0x3c0
[<ffffffff885f5758>] x86_64_start_reservations+0x18/0x30
[<ffffffff885f582b>] x86_64_start_kernel+0x7b/0x80
[<ffffffff83a001c3>] secondary_startup_64_no_verify+0x15e/0x16b

Link: https://lore.kernel.org/linux-trace-kernel/87r0hfnr9r.fsf@kernel.org/
Link: https://lore.kernel.org/linux-trace-kernel/20240214112046.09a322d6@gandalf.local.home

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Fixes: 44dc5c41b5b1 ("tracing: Fix wasted memory in saved_cmdlines logic")
Reported-by: Kalle Valo <kvalo@kernel.org>
Tested-by: Kalle Valo <kvalo@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/trace/trace.c | 3 +++
1 file changed, 3 insertions(+)

--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -40,6 +40,7 @@
#include <linux/ctype.h>
#include <linux/init.h>
#include <linux/panic_notifier.h>
+#include <linux/kmemleak.h>
#include <linux/poll.h>
#include <linux/nmi.h>
#include <linux/fs.h>
@@ -2268,6 +2269,7 @@ static void free_saved_cmdlines_buffer(s
int order = get_order(sizeof(*s) + s->cmdline_num * TASK_COMM_LEN);

kfree(s->map_cmdline_to_pid);
+ kmemleak_free(s);
free_pages((unsigned long)s, order);
}

@@ -2287,6 +2289,7 @@ static struct saved_cmdlines_buffer *all
return NULL;

s = page_address(page);
+ kmemleak_alloc(s, size, 1, GFP_KERNEL);
memset(s, 0, sizeof(*s));

/* Round up to actual allocation */