[PATCH v6 3/3] include: Set tsk->comm length to 64 bytes

Bhupesh
2025-07-24T12:36:50Z

Historically due to the 16-byte length of TASK_COMM_LEN, the
users of 'tsk->comm' are restricted to use a fixed-size target
buffer also of TASK_COMM_LEN for 'memcpy()' like use-cases.

To fix the same, we now use a 64-byte TASK_COMM_EXT_LEN and
set the comm element inside 'task_struct' to the same length:
struct task_struct {
.....
char comm[TASK_COMM_EXT_LEN];
.....
};

where TASK_COMM_EXT_LEN is 64-bytes.

Now, in order to maintain existing ABI, we ensure that:

- Existing users of 'get_task_comm'/ 'set_task_comm' will get 'tsk->comm'
truncated to a maximum of 'TASK_COMM_LEN' (16-bytes) to maintain ABI,
- New / Modified users of 'get_task_comm'/ 'set_task_comm' will get
'tsk->comm' supported up to the maximum of 'TASK_COMM_EXT_LEN' (64-bytes).

Note, that the existing users have not been modified to migrate to
'TASK_COMM_EXT_LEN', in case they have hard-coded expectations of
dealing with only a 'TASK_COMM_LEN' long 'tsk->comm'.

Signed-off-by: Bhupesh <bhupesh@igalia.com>
---
include/linux/sched.h | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 8bbd03f1b978..b6abb759292c 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -317,6 +317,7 @@ struct user_event_mm;
*/
enum {
TASK_COMM_LEN = 16,
+ TASK_COMM_EXT_LEN = 64,
};

extern void sched_tick(void);
@@ -1159,7 +1160,7 @@ struct task_struct {
* - logic inside set_task_comm() will ensure it is always NUL-terminated and
* zero-padded
*/
- char comm[TASK_COMM_LEN];
+ char comm[TASK_COMM_EXT_LEN];

struct nameidata *nameidata;

@@ -1954,7 +1955,7 @@ extern void kick_process(struct task_struct *tsk);

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); \
+ BUILD_BUG_ON(sizeof(from) < TASK_COMM_LEN); \
__set_task_comm(tsk, from, false); \
})

@@ -1974,6 +1975,10 @@ extern void __set_task_comm(struct task_struct *tsk, const char *from, bool exec
#define get_task_comm(buf, tsk) ({ \
BUILD_BUG_ON(sizeof(buf) < TASK_COMM_LEN); \
strscpy_pad(buf, (tsk)->comm); \
+ if ((sizeof(buf)) == TASK_COMM_LEN) \
+ buf[TASK_COMM_LEN - 1] = '\0'; \
+ else \
+ buf[TASK_COMM_EXT_LEN - 1] = '\0'; \
buf; \
})

--
2.38.1