As Linus mentioned in [1], currently we have several memcpy() use-cases
which use 'current->comm' to copy the task name over to local copies.
For an example:
...
char comm[TASK_COMM_LEN];
memcpy(comm, current->comm, TASK_COMM_LEN);
...
These should be rather calling a wrappper like "get_task_array()",
which is implemented as:
static __always_inline void
__cstr_array_copy(char *dst,
const char *src, __kernel_size_t size)
{
memcpy(dst, src, size);
dst[size] = 0;
}
#define get_task_array(dst,src) \
__cstr_array_copy(dst, src, __must_be_array(dst))
The relevant 'memcpy()' users were identified using the following search
pattern:
$ git grep 'memcpy.*->comm\>'
Link: https://lore.kernel.org/all/CAHk-=wi5c=_-FBGo_88CowJd_F-Gi6Ud9d=TALm65ReN7YjrMw@mail.gmail.com/ #1
Signed-off-by: Bhupesh <bhupesh@igalia.com>
---
include/linux/coredump.h | 2 +-
include/linux/sched.h | 32 +++++++++++++++++++
include/linux/tracepoint.h | 4 +--
include/trace/events/block.h | 10 +++---
include/trace/events/oom.h | 2 +-
include/trace/events/osnoise.h | 2 +-
include/trace/events/sched.h | 13 ++++----
include/trace/events/signal.h | 2 +-
include/trace/events/task.h | 4 +--
tools/bpf/bpftool/pids.c | 6 ++--
.../bpf/test_kmods/bpf_testmod-events.h | 2 +-
11 files changed, 54 insertions(+), 25 deletions(-)
diff --git a/include/linux/coredump.h b/include/linux/coredump.h
index 68861da4cf7c..bcee0afc5eaf 100644
--- a/include/linux/coredump.h
+++ b/include/linux/coredump.h
@@ -54,7 +54,7 @@ extern void vfs_coredump(const kernel_siginfo_t *siginfo);
do { \
char comm[TASK_COMM_LEN]; \
/* This will always be NUL terminated. */ \
- memcpy(comm, current->comm, sizeof(comm)); \
+ get_task_array(comm, current->comm); \
printk_ratelimited(Level "coredump: %d(%*pE): " Format "\n", \
task_tgid_vnr(current), (int)strlen(comm), comm, ##__VA_ARGS__); \
} while (0) \
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 5a58c1270474..d26d1dfb9904 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1960,12 +1960,44 @@ extern void wake_up_new_task(struct task_struct *tsk);
extern void kick_process(struct task_struct *tsk);
+/*
+ * - Why not use task_lock()?
+ * User space can randomly change their names anyway, so locking for readers
+ * doesn't make sense. For writers, locking is probably necessary, as a race
+ * condition could lead to long-term mixed results.
+ * The logic inside __set_task_comm() should ensure that the task comm is
+ * always NUL-terminated and zero-padded. Therefore the race condition between
+ * reader and writer is not an issue.
+ */
+
extern void __set_task_comm(struct task_struct *tsk, const char *from, bool exec);
#define set_task_comm(tsk, from) ({ \
BUILD_BUG_ON(sizeof(from) < TASK_COMM_LEN); \
__set_task_comm(tsk, from, false); \
})
+/*
+ * 'get_task_array' can be 'data-racy' in the destination and
+ * should not be used for cases where a 'stable NUL at the end'
+ * is needed. Its better to use strscpy and friends for such
+ * use-cases.
+ *
+ * It is suited mainly for a 'just copy comm to a constant-sized
+ * array' case - especially in performance sensitive use-cases,
+ * like tracing.
+ */
+
+static __always_inline void
+ __cstr_array_copy(char *dst, const char *src,
+ __kernel_size_t size)
+{
+ memcpy(dst, src, size);
+ dst[size] = 0;
+}
+
+#define get_task_array(dst, src) \
+ __cstr_array_copy(dst, src, __must_be_array(dst))
+
static __always_inline void scheduler_ipi(void)
{
/*
diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index 826ce3f8e1f8..40e04cb660ce 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -570,10 +570,10 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
* *
*
* TP_fast_assign(
- * memcpy(__entry->next_comm, next->comm, TASK_COMM_LEN);
+ * get_task_array(__entry->next_comm, next->comm);
* __entry->prev_pid = prev->pid;
* __entry->prev_prio = prev->prio;
- * memcpy(__entry->prev_comm, prev->comm, TASK_COMM_LEN);
+ * get_task_array(__entry->prev_comm, prev->comm);
* __entry->next_pid = next->pid;
* __entry->next_prio = next->prio;
* ),
diff --git a/include/trace/events/block.h b/include/trace/events/block.h
index 6aa79e2d799c..de1fe35333fc 100644
--- a/include/trace/events/block.h
+++ b/include/trace/events/block.h
@@ -213,7 +213,7 @@ DECLARE_EVENT_CLASS(block_rq,
blk_fill_rwbs(__entry->rwbs, rq->cmd_flags);
__get_str(cmd)[0] = '\0';
- memcpy(__entry->comm, current->comm, TASK_COMM_LEN);
+ get_task_array(__entry->comm, current->comm);
),
TP_printk("%d,%d %s %u (%s) %llu + %u %s,%u,%u [%s]",
@@ -351,7 +351,7 @@ DECLARE_EVENT_CLASS(block_bio,
__entry->sector = bio->bi_iter.bi_sector;
__entry->nr_sector = bio_sectors(bio);
blk_fill_rwbs(__entry->rwbs, bio->bi_opf);
- memcpy(__entry->comm, current->comm, TASK_COMM_LEN);
+ get_task_array(__entry->comm, current->comm);
),
TP_printk("%d,%d %s %llu + %u [%s]",
@@ -434,7 +434,7 @@ TRACE_EVENT(block_plug,
),
TP_fast_assign(
- memcpy(__entry->comm, current->comm, TASK_COMM_LEN);
+ get_task_array(__entry->comm, current->comm);
),
TP_printk("[%s]", __entry->comm)
@@ -453,7 +453,7 @@ DECLARE_EVENT_CLASS(block_unplug,
TP_fast_assign(
__entry->nr_rq = depth;
- memcpy(__entry->comm, current->comm, TASK_COMM_LEN);
+ get_task_array(__entry->comm, current->comm);
),
TP_printk("[%s] %d", __entry->comm, __entry->nr_rq)
@@ -504,7 +504,7 @@ TRACE_EVENT(block_split,
__entry->sector = bio->bi_iter.bi_sector;
__entry->new_sector = new_sector;
blk_fill_rwbs(__entry->rwbs, bio->bi_opf);
- memcpy(__entry->comm, current->comm, TASK_COMM_LEN);
+ get_task_array(__entry->comm, current->comm);
),
TP_printk("%d,%d %s %llu / %llu [%s]",
diff --git a/include/trace/events/oom.h b/include/trace/events/oom.h
index 9f0a5d1482c4..31e5b7295188 100644
--- a/include/trace/events/oom.h
+++ b/include/trace/events/oom.h
@@ -23,7 +23,7 @@ TRACE_EVENT(oom_score_adj_update,
TP_fast_assign(
__entry->pid = task->pid;
- memcpy(__entry->comm, task->comm, TASK_COMM_LEN);
+ get_task_array(__entry->comm, task->comm);
__entry->oom_score_adj = task->signal->oom_score_adj;
),
diff --git a/include/trace/events/osnoise.h b/include/trace/events/osnoise.h
index 3f4273623801..f67f8b5eca75 100644
--- a/include/trace/events/osnoise.h
+++ b/include/trace/events/osnoise.h
@@ -116,7 +116,7 @@ TRACE_EVENT(thread_noise,
),
TP_fast_assign(
- memcpy(__entry->comm, t->comm, TASK_COMM_LEN);
+ get_task_array(__entry->comm, t->comm);
__entry->pid = t->pid;
__entry->start = start;
__entry->duration = duration;
diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
index 7b2645b50e78..66fe808f2654 100644
--- a/include/trace/events/sched.h
+++ b/include/trace/events/sched.h
@@ -152,7 +152,7 @@ DECLARE_EVENT_CLASS(sched_wakeup_template,
),
TP_fast_assign(
- memcpy(__entry->comm, p->comm, TASK_COMM_LEN);
+ get_task_array(__entry->comm, p->comm);
__entry->pid = p->pid;
__entry->prio = p->prio; /* XXX SCHED_DEADLINE */
__entry->target_cpu = task_cpu(p);
@@ -237,11 +237,11 @@ TRACE_EVENT(sched_switch,
),
TP_fast_assign(
- memcpy(__entry->prev_comm, prev->comm, TASK_COMM_LEN);
+ get_task_array(__entry->prev_comm, prev->comm);
__entry->prev_pid = prev->pid;
__entry->prev_prio = prev->prio;
__entry->prev_state = __trace_sched_switch_state(preempt, prev_state, prev);
- memcpy(__entry->next_comm, next->comm, TASK_COMM_LEN);
+ get_task_array(__entry->next_comm, next->comm);
__entry->next_pid = next->pid;
__entry->next_prio = next->prio;
/* XXX SCHED_DEADLINE */
@@ -346,7 +346,7 @@ TRACE_EVENT(sched_process_exit,
),
TP_fast_assign(
- memcpy(__entry->comm, p->comm, TASK_COMM_LEN);
+ get_task_array(__entry->comm, p->comm);
__entry->pid = p->pid;
__entry->prio = p->prio; /* XXX SCHED_DEADLINE */
__entry->group_dead = group_dead;
@@ -787,14 +787,13 @@ TRACE_EVENT(sched_skip_cpuset_numa,
),
TP_fast_assign(
- memcpy(__entry->comm, tsk->comm, TASK_COMM_LEN);
+ get_task_array(__entry->comm, tsk->comm);
__entry->pid = task_pid_nr(tsk);
__entry->tgid = task_tgid_nr(tsk);
__entry->ngid = task_numa_group_id(tsk);
BUILD_BUG_ON(sizeof(nodemask_t) != \
BITS_TO_LONGS(MAX_NUMNODES) * sizeof(long));
- memcpy(__entry->mem_allowed, mem_allowed_ptr->bits,
- sizeof(__entry->mem_allowed));
+ get_task_array(__entry->mem_allowed, mem_allowed_ptr->bits);
),
TP_printk("comm=%s pid=%d tgid=%d ngid=%d mem_nodes_allowed=%*pbl",
diff --git a/include/trace/events/signal.h b/include/trace/events/signal.h
index 1db7e4b07c01..0681dc5ab1de 100644
--- a/include/trace/events/signal.h
+++ b/include/trace/events/signal.h
@@ -67,7 +67,7 @@ TRACE_EVENT(signal_generate,
TP_fast_assign(
__entry->sig = sig;
TP_STORE_SIGINFO(__entry, info);
- memcpy(__entry->comm, task->comm, TASK_COMM_LEN);
+ get_task_array(__entry->comm, task->comm);
__entry->pid = task->pid;
__entry->group = group;
__entry->result = result;
diff --git a/include/trace/events/task.h b/include/trace/events/task.h
index af535b053033..9553946943a6 100644
--- a/include/trace/events/task.h
+++ b/include/trace/events/task.h
@@ -21,7 +21,7 @@ TRACE_EVENT(task_newtask,
TP_fast_assign(
__entry->pid = task->pid;
- memcpy(__entry->comm, task->comm, TASK_COMM_LEN);
+ get_task_array(__entry->comm, task->comm);
__entry->clone_flags = clone_flags;
__entry->oom_score_adj = task->signal->oom_score_adj;
),
@@ -44,7 +44,7 @@ TRACE_EVENT(task_rename,
),
TP_fast_assign(
- memcpy(entry->oldcomm, task->comm, TASK_COMM_LEN);
+ get_task_array(entry->oldcomm, task->comm);
strscpy(entry->newcomm, comm, TASK_COMM_LEN);
__entry->oom_score_adj = task->signal->oom_score_adj;
),
diff --git a/tools/bpf/bpftool/pids.c b/tools/bpf/bpftool/pids.c
index 23f488cf1740..a5d339cb8ca3 100644
--- a/tools/bpf/bpftool/pids.c
+++ b/tools/bpf/bpftool/pids.c
@@ -53,8 +53,7 @@ static void add_ref(struct hashmap *map, struct pid_iter_entry *e)
refs->refs = tmp;
ref = &refs->refs[refs->ref_cnt];
ref->pid = e->pid;
- memcpy(ref->comm, e->comm, sizeof(ref->comm));
- ref->comm[sizeof(ref->comm) - 1] = '\0';
+ get_task_array(ref->comm, e->comm);
refs->ref_cnt++;
return;
@@ -77,8 +76,7 @@ static void add_ref(struct hashmap *map, struct pid_iter_entry *e)
}
ref = &refs->refs[0];
ref->pid = e->pid;
- memcpy(ref->comm, e->comm, sizeof(ref->comm));
- ref->comm[sizeof(ref->comm) - 1] = '\0';
+ get_task_array(ref->comm, e->comm);
refs->ref_cnt = 1;
refs->has_bpf_cookie = e->has_bpf_cookie;
refs->bpf_cookie = e->bpf_cookie;
diff --git a/tools/testing/selftests/bpf/test_kmods/bpf_testmod-events.h b/tools/testing/selftests/bpf/test_kmods/bpf_testmod-events.h
index aeef86b3da74..81880748550f 100644
--- a/tools/testing/selftests/bpf/test_kmods/bpf_testmod-events.h
+++ b/tools/testing/selftests/bpf/test_kmods/bpf_testmod-events.h
@@ -20,7 +20,7 @@ TRACE_EVENT(bpf_testmod_test_read,
),
TP_fast_assign(
__entry->pid = task->pid;
- memcpy(__entry->comm, task->comm, TASK_COMM_LEN);
+ get_task_array(__entry->comm, task->comm);
__entry->off = ctx->off;
__entry->len = ctx->len;
),
--
2.38.1On Thu, Aug 21, 2025 at 03:51:51PM +0530, Bhupesh wrote:
> As Linus mentioned in [1], currently we have several memcpy() use-cases
> which use 'current->comm' to copy the task name over to local copies.
> For an example:
>
> ...
> char comm[TASK_COMM_LEN];
> memcpy(comm, current->comm, TASK_COMM_LEN);
> ...
>
> These should be rather calling a wrappper like "get_task_array()",
> which is implemented as:
>
> static __always_inline void
> __cstr_array_copy(char *dst,
> const char *src, __kernel_size_t size)
> {
> memcpy(dst, src, size);
> dst[size] = 0;
> }
>
> #define get_task_array(dst,src) \
> __cstr_array_copy(dst, src, __must_be_array(dst))
>
> The relevant 'memcpy()' users were identified using the following search
> pattern:
> $ git grep 'memcpy.*->comm\>'
>
> Link: https://lore.kernel.org/all/CAHk-=wi5c=_-FBGo_88CowJd_F-Gi6Ud9d=TALm65ReN7YjrMw@mail.gmail.com/ #1
>
> Signed-off-by: Bhupesh <bhupesh@igalia.com>
> ---
> include/linux/coredump.h | 2 +-
> include/linux/sched.h | 32 +++++++++++++++++++
> include/linux/tracepoint.h | 4 +--
> include/trace/events/block.h | 10 +++---
> include/trace/events/oom.h | 2 +-
> include/trace/events/osnoise.h | 2 +-
> include/trace/events/sched.h | 13 ++++----
> include/trace/events/signal.h | 2 +-
> include/trace/events/task.h | 4 +--
> tools/bpf/bpftool/pids.c | 6 ++--
> .../bpf/test_kmods/bpf_testmod-events.h | 2 +-
> 11 files changed, 54 insertions(+), 25 deletions(-)
>
> diff --git a/include/linux/coredump.h b/include/linux/coredump.h
> index 68861da4cf7c..bcee0afc5eaf 100644
> --- a/include/linux/coredump.h
> +++ b/include/linux/coredump.h
> @@ -54,7 +54,7 @@ extern void vfs_coredump(const kernel_siginfo_t *siginfo);
> do { \
> char comm[TASK_COMM_LEN]; \
> /* This will always be NUL terminated. */ \
> - memcpy(comm, current->comm, sizeof(comm)); \
> + get_task_array(comm, current->comm); \
> printk_ratelimited(Level "coredump: %d(%*pE): " Format "\n", \
> task_tgid_vnr(current), (int)strlen(comm), comm, ##__VA_ARGS__); \
> } while (0) \
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 5a58c1270474..d26d1dfb9904 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1960,12 +1960,44 @@ extern void wake_up_new_task(struct task_struct *tsk);
>
> extern void kick_process(struct task_struct *tsk);
>
> +/*
> + * - Why not use task_lock()?
> + * User space can randomly change their names anyway, so locking for readers
> + * doesn't make sense. For writers, locking is probably necessary, as a race
> + * condition could lead to long-term mixed results.
> + * The logic inside __set_task_comm() should ensure that the task comm is
> + * always NUL-terminated and zero-padded. Therefore the race condition between
> + * reader and writer is not an issue.
> + */
> +
> extern void __set_task_comm(struct task_struct *tsk, const char *from, bool exec);
> #define set_task_comm(tsk, from) ({ \
> BUILD_BUG_ON(sizeof(from) < TASK_COMM_LEN); \
> __set_task_comm(tsk, from, false); \
> })
>
> +/*
> + * 'get_task_array' can be 'data-racy' in the destination and
> + * should not be used for cases where a 'stable NUL at the end'
> + * is needed. Its better to use strscpy and friends for such
> + * use-cases.
> + *
> + * It is suited mainly for a 'just copy comm to a constant-sized
> + * array' case - especially in performance sensitive use-cases,
> + * like tracing.
> + */
> +
> +static __always_inline void
> + __cstr_array_copy(char *dst, const char *src,
> + __kernel_size_t size)
> +{
> + memcpy(dst, src, size);
> + dst[size] = 0;
> +}
Please don't reinvent the wheel. :) We already have memtostr, please use
that (or memtostr_pad).
> +
> +#define get_task_array(dst, src) \
> + __cstr_array_copy(dst, src, __must_be_array(dst))
Uh, __must_be_array(dst) returns 0 on success. :P Are you sure you
tested this?
--
Kees Cook
Hi Kees,
On 8/25/25 7:31 PM, Kees Cook wrote:
> On Thu, Aug 21, 2025 at 03:51:51PM +0530, Bhupesh wrote:
>> As Linus mentioned in [1], currently we have several memcpy() use-cases
>> which use 'current->comm' to copy the task name over to local copies.
>> For an example:
>>
>> ...
>> char comm[TASK_COMM_LEN];
>> memcpy(comm, current->comm, TASK_COMM_LEN);
>> ...
>>
>> These should be rather calling a wrappper like "get_task_array()",
>> which is implemented as:
>>
>> static __always_inline void
>> __cstr_array_copy(char *dst,
>> const char *src, __kernel_size_t size)
>> {
>> memcpy(dst, src, size);
>> dst[size] = 0;
>> }
>>
>> #define get_task_array(dst,src) \
>> __cstr_array_copy(dst, src, __must_be_array(dst))
>>
>> The relevant 'memcpy()' users were identified using the following search
>> pattern:
>> $ git grep 'memcpy.*->comm\>'
>>
>> Link:https://lore.kernel.org/all/CAHk-=wi5c=_-FBGo_88CowJd_F-Gi6Ud9d=TALm65ReN7YjrMw@mail.gmail.com/ #1
>>
>> Signed-off-by: Bhupesh<bhupesh@igalia.com>
>> ---
>> include/linux/coredump.h | 2 +-
>> include/linux/sched.h | 32 +++++++++++++++++++
>> include/linux/tracepoint.h | 4 +--
>> include/trace/events/block.h | 10 +++---
>> include/trace/events/oom.h | 2 +-
>> include/trace/events/osnoise.h | 2 +-
>> include/trace/events/sched.h | 13 ++++----
>> include/trace/events/signal.h | 2 +-
>> include/trace/events/task.h | 4 +--
>> tools/bpf/bpftool/pids.c | 6 ++--
>> .../bpf/test_kmods/bpf_testmod-events.h | 2 +-
>> 11 files changed, 54 insertions(+), 25 deletions(-)
>>
>> diff --git a/include/linux/coredump.h b/include/linux/coredump.h
>> index 68861da4cf7c..bcee0afc5eaf 100644
>> --- a/include/linux/coredump.h
>> +++ b/include/linux/coredump.h
>> @@ -54,7 +54,7 @@ extern void vfs_coredump(const kernel_siginfo_t *siginfo);
>> do { \
>> char comm[TASK_COMM_LEN]; \
>> /* This will always be NUL terminated. */ \
>> - memcpy(comm, current->comm, sizeof(comm)); \
>> + get_task_array(comm, current->comm); \
>> printk_ratelimited(Level "coredump: %d(%*pE): " Format "\n", \
>> task_tgid_vnr(current), (int)strlen(comm), comm, ##__VA_ARGS__); \
>> } while (0) \
>> diff --git a/include/linux/sched.h b/include/linux/sched.h
>> index 5a58c1270474..d26d1dfb9904 100644
>> --- a/include/linux/sched.h
>> +++ b/include/linux/sched.h
>> @@ -1960,12 +1960,44 @@ extern void wake_up_new_task(struct task_struct *tsk);
>>
>> extern void kick_process(struct task_struct *tsk);
>>
>> +/*
>> + * - Why not use task_lock()?
>> + * User space can randomly change their names anyway, so locking for readers
>> + * doesn't make sense. For writers, locking is probably necessary, as a race
>> + * condition could lead to long-term mixed results.
>> + * The logic inside __set_task_comm() should ensure that the task comm is
>> + * always NUL-terminated and zero-padded. Therefore the race condition between
>> + * reader and writer is not an issue.
>> + */
>> +
>> extern void __set_task_comm(struct task_struct *tsk, const char *from, bool exec);
>> #define set_task_comm(tsk, from) ({ \
>> BUILD_BUG_ON(sizeof(from) < TASK_COMM_LEN); \
>> __set_task_comm(tsk, from, false); \
>> })
>>
>> +/*
>> + * 'get_task_array' can be 'data-racy' in the destination and
>> + * should not be used for cases where a 'stable NUL at the end'
>> + * is needed. Its better to use strscpy and friends for such
>> + * use-cases.
>> + *
>> + * It is suited mainly for a 'just copy comm to a constant-sized
>> + * array' case - especially in performance sensitive use-cases,
>> + * like tracing.
>> + */
>> +
>> +static __always_inline void
>> + __cstr_array_copy(char *dst, const char *src,
>> + __kernel_size_t size)
>> +{
>> + memcpy(dst, src, size);
>> + dst[size] = 0;
>> +}
> Please don't reinvent the wheel. :) We already have memtostr, please use
> that (or memtostr_pad).
Sure, but wouldn't we get a static assertion failure: "must be array"
for memtostr() usage, because of the following:
#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]) +
__must_be_array(arr))
I think it would be easier just to set:
memcpy(dst, src, size);
dst[size -1] = 0;
instead as Linus and Steven suggested.
Thanks,
Bhupesh
>> +
>> +#define get_task_array(dst, src) \
>> + __cstr_array_copy(dst, src, __must_be_array(dst))
> Uh, __must_be_array(dst) returns 0 on success. :P Are you sure you
> tested this?
>
On Mon, 1 Sep 2025 10:58:17 +0530
Bhupesh Sharma <bhsharma@igalia.com> wrote:
> Hi Kees,
>
> On 8/25/25 7:31 PM, Kees Cook wrote:
> > On Thu, Aug 21, 2025 at 03:51:51PM +0530, Bhupesh wrote:
> >> As Linus mentioned in [1], currently we have several memcpy() use-cases
> >> which use 'current->comm' to copy the task name over to local copies.
> >> For an example:
> >>
> >> ...
> >> char comm[TASK_COMM_LEN];
> >> memcpy(comm, current->comm, TASK_COMM_LEN);
> >> ...
> >>
> >> These should be rather calling a wrappper like "get_task_array()",
> >> which is implemented as:
> >>
> >> static __always_inline void
> >> __cstr_array_copy(char *dst,
> >> const char *src, __kernel_size_t size)
> >> {
> >> memcpy(dst, src, size);
> >> dst[size] = 0;
> >> }
> >>
> >> #define get_task_array(dst,src) \
> >> __cstr_array_copy(dst, src, __must_be_array(dst))
> >>
> >> The relevant 'memcpy()' users were identified using the following search
> >> pattern:
> >> $ git grep 'memcpy.*->comm\>'
> >>
> >> Link:https://lore.kernel.org/all/CAHk-=wi5c=_-FBGo_88CowJd_F-Gi6Ud9d=TALm65ReN7YjrMw@mail.gmail.com/ #1
> >>
> >> Signed-off-by: Bhupesh<bhupesh@igalia.com>
> >> ---
> >> include/linux/coredump.h | 2 +-
> >> include/linux/sched.h | 32 +++++++++++++++++++
> >> include/linux/tracepoint.h | 4 +--
> >> include/trace/events/block.h | 10 +++---
> >> include/trace/events/oom.h | 2 +-
> >> include/trace/events/osnoise.h | 2 +-
> >> include/trace/events/sched.h | 13 ++++----
> >> include/trace/events/signal.h | 2 +-
> >> include/trace/events/task.h | 4 +--
> >> tools/bpf/bpftool/pids.c | 6 ++--
> >> .../bpf/test_kmods/bpf_testmod-events.h | 2 +-
> >> 11 files changed, 54 insertions(+), 25 deletions(-)
> >>
> >> diff --git a/include/linux/coredump.h b/include/linux/coredump.h
> >> index 68861da4cf7c..bcee0afc5eaf 100644
> >> --- a/include/linux/coredump.h
> >> +++ b/include/linux/coredump.h
> >> @@ -54,7 +54,7 @@ extern void vfs_coredump(const kernel_siginfo_t *siginfo);
> >> do { \
> >> char comm[TASK_COMM_LEN]; \
> >> /* This will always be NUL terminated. */ \
> >> - memcpy(comm, current->comm, sizeof(comm)); \
> >> + get_task_array(comm, current->comm); \
> >> printk_ratelimited(Level "coredump: %d(%*pE): " Format "\n", \
> >> task_tgid_vnr(current), (int)strlen(comm), comm, ##__VA_ARGS__); \
> >> } while (0) \
> >> diff --git a/include/linux/sched.h b/include/linux/sched.h
> >> index 5a58c1270474..d26d1dfb9904 100644
> >> --- a/include/linux/sched.h
> >> +++ b/include/linux/sched.h
> >> @@ -1960,12 +1960,44 @@ extern void wake_up_new_task(struct task_struct *tsk);
> >>
> >> extern void kick_process(struct task_struct *tsk);
> >>
> >> +/*
> >> + * - Why not use task_lock()?
> >> + * User space can randomly change their names anyway, so locking for readers
> >> + * doesn't make sense. For writers, locking is probably necessary, as a race
> >> + * condition could lead to long-term mixed results.
> >> + * The logic inside __set_task_comm() should ensure that the task comm is
> >> + * always NUL-terminated and zero-padded. Therefore the race condition between
> >> + * reader and writer is not an issue.
> >> + */
> >> +
> >> extern void __set_task_comm(struct task_struct *tsk, const char *from, bool exec);
> >> #define set_task_comm(tsk, from) ({ \
> >> BUILD_BUG_ON(sizeof(from) < TASK_COMM_LEN); \
> >> __set_task_comm(tsk, from, false); \
> >> })
> >>
> >> +/*
> >> + * 'get_task_array' can be 'data-racy' in the destination and
> >> + * should not be used for cases where a 'stable NUL at the end'
> >> + * is needed. Its better to use strscpy and friends for such
> >> + * use-cases.
> >> + *
> >> + * It is suited mainly for a 'just copy comm to a constant-sized
> >> + * array' case - especially in performance sensitive use-cases,
> >> + * like tracing.
> >> + */
> >> +
> >> +static __always_inline void
> >> + __cstr_array_copy(char *dst, const char *src,
> >> + __kernel_size_t size)
> >> +{
> >> + memcpy(dst, src, size);
> >> + dst[size] = 0;
> >> +}
> > Please don't reinvent the wheel. :) We already have memtostr, please use
> > that (or memtostr_pad).
>
> Sure, but wouldn't we get a static assertion failure: "must be array"
> for memtostr() usage, because of the following:
>
> #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]) +
> __must_be_array(arr))
>
> I think it would be easier just to set:
>
> memcpy(dst, src, size);
> dst[size -1] = 0;
>
> instead as Linus and Steven suggested.
The compiler is still likely to make a mess of it.
You really want:
*(u64 *)dst = *(u64 *)src;
*(u64 *)(dst + 8) = *(u64 *)(src + 8) & ~htobe64(0xff);
That may need something to force 8 byte alignment.
Or force 4 byte alignment and use a u64 type with 4 byte alignment.
David
>
> Thanks,
> Bhupesh
>
> >> +
> >> +#define get_task_array(dst, src) \
> >> + __cstr_array_copy(dst, src, __must_be_array(dst))
> > Uh, __must_be_array(dst) returns 0 on success. :P Are you sure you
> > tested this?
> >
>
>
On Thu, 21 Aug 2025 15:51:51 +0530
Bhupesh <bhupesh@igalia.com> wrote:
> +static __always_inline void
> + __cstr_array_copy(char *dst, const char *src,
> + __kernel_size_t size)
> +{
> + memcpy(dst, src, size);
> + dst[size] = 0;
Shouldn't this be: dst[size - 1] = 0;
?
Perhaps also add:
BUILD_BUG_ON(size == 0);
-- Steve
> +}
> +
On 8/21/25 10:13 PM, Steven Rostedt wrote:
> On Thu, 21 Aug 2025 15:51:51 +0530
> Bhupesh <bhupesh@igalia.com> wrote:
>
>> +static __always_inline void
>> + __cstr_array_copy(char *dst, const char *src,
>> + __kernel_size_t size)
>> +{
>> + memcpy(dst, src, size);
>> + dst[size] = 0;
> Shouldn't this be: dst[size - 1] = 0;
>
> ?
>
> Perhaps also add:
>
> BUILD_BUG_ON(size == 0);
>
>
Ok, will add this in v9.
Thanks.
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