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

Bhupesh posted 3 patches 6 months, 2 weeks ago
There is a newer version of this series
[PATCH v6 3/3] include: Set tsk->comm length to 64 bytes
Posted by Bhupesh 6 months, 2 weeks ago 
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
Re: [PATCH v6 3/3] include: Set tsk->comm length to 64 bytes
Posted by kernel test robot 6 months, 2 weeks ago 
Hi Bhupesh,

kernel test robot noticed the following build warnings:

[auto build test WARNING on trace/for-next]
[also build test WARNING on tip/sched/core akpm-mm/mm-everything linus/master v6.16-rc7 next-20250725]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Bhupesh/exec-Remove-obsolete-comments/20250724-203927
base:   https://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace for-next
patch link:    https://lore.kernel.org/r/20250724123612.206110-4-bhupesh%40igalia.com
patch subject: [PATCH v6 3/3] include: Set tsk->comm length to 64 bytes
config: sparc64-randconfig-001-20250725 (https://download.01.org/0day-ci/archive/20250726/202507261841.Z2C9RmTJ-lkp@intel.com/config)
compiler: sparc64-linux-gcc (GCC) 8.5.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250726/202507261841.Z2C9RmTJ-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202507261841.Z2C9RmTJ-lkp@intel.com/

All warnings (new ones prefixed by >>):

   drivers/gpu/drm/nouveau/nouveau_chan.c: In function 'nouveau_channel_ctor':
>> drivers/gpu/drm/nouveau/nouveau_chan.c:336:51: warning: '%s' directive output may be truncated writing up to 63 bytes into a region of size 32 [-Wformat-truncation=]
     snprintf(args->name, __member_size(args->name), "%s[%d]",
                                                      ^~
   drivers/gpu/drm/nouveau/nouveau_chan.c:336:2: note: 'snprintf' output between 4 and 77 bytes into a destination of size 32
     snprintf(args->name, __member_size(args->name), "%s[%d]",
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
       current->comm, task_pid_nr(current));
       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--
   drivers/gpu/drm/nouveau/nouveau_drm.c: In function 'nouveau_drm_open':
>> drivers/gpu/drm/nouveau/nouveau_drm.c:1202:32: warning: '%s' directive output may be truncated writing up to 63 bytes into a region of size 32 [-Wformat-truncation=]
     snprintf(name, sizeof(name), "%s[%d]",
                                   ^~
   drivers/gpu/drm/nouveau/nouveau_drm.c:1202:2: note: 'snprintf' output between 4 and 77 bytes into a destination of size 32
     snprintf(name, sizeof(name), "%s[%d]",
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
       current->comm, pid_nr(rcu_dereference(fpriv->pid)));
       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


vim +336 drivers/gpu/drm/nouveau/nouveau_chan.c

ebb945a94bba2c Ben Skeggs          2012-07-20  246  
5b8a43aeb9cbf6 Marcin Slusarz      2012-08-19  247  static int
5cca41ac70e587 Ben Skeggs          2024-07-26  248  nouveau_channel_ctor(struct nouveau_cli *cli, bool priv, u64 runm,
06db7fded6dec8 Ben Skeggs          2022-06-01  249  		     struct nouveau_channel **pchan)
ebb945a94bba2c Ben Skeggs          2012-07-20  250  {
152be54224de18 Danilo Krummrich    2023-10-02  251  	const struct nvif_mclass hosts[] = {
284ad706ad2f50 Ben Skeggs          2025-02-04  252  		{ BLACKWELL_CHANNEL_GPFIFO_B, 0 },
32cb1cc358ffed Ben Skeggs          2024-11-25  253  		{ BLACKWELL_CHANNEL_GPFIFO_A, 0 },
44f93b209e2afd Ben Skeggs          2024-11-25  254  		{    HOPPER_CHANNEL_GPFIFO_A, 0 },
06db7fded6dec8 Ben Skeggs          2022-06-01  255  		{    AMPERE_CHANNEL_GPFIFO_B, 0 },
7f4f35ea5b080e Ben Skeggs          2022-06-01  256  		{    AMPERE_CHANNEL_GPFIFO_A, 0 },
06db7fded6dec8 Ben Skeggs          2022-06-01  257  		{    TURING_CHANNEL_GPFIFO_A, 0 },
06db7fded6dec8 Ben Skeggs          2022-06-01  258  		{     VOLTA_CHANNEL_GPFIFO_A, 0 },
06db7fded6dec8 Ben Skeggs          2022-06-01  259  		{    PASCAL_CHANNEL_GPFIFO_A, 0 },
06db7fded6dec8 Ben Skeggs          2022-06-01  260  		{   MAXWELL_CHANNEL_GPFIFO_A, 0 },
06db7fded6dec8 Ben Skeggs          2022-06-01  261  		{    KEPLER_CHANNEL_GPFIFO_B, 0 },
06db7fded6dec8 Ben Skeggs          2022-06-01  262  		{    KEPLER_CHANNEL_GPFIFO_A, 0 },
06db7fded6dec8 Ben Skeggs          2022-06-01  263  		{     FERMI_CHANNEL_GPFIFO  , 0 },
06db7fded6dec8 Ben Skeggs          2022-06-01  264  		{       G82_CHANNEL_GPFIFO  , 0 },
06db7fded6dec8 Ben Skeggs          2022-06-01  265  		{      NV50_CHANNEL_GPFIFO  , 0 },
06db7fded6dec8 Ben Skeggs          2022-06-01  266  		{      NV40_CHANNEL_DMA     , 0 },
06db7fded6dec8 Ben Skeggs          2022-06-01  267  		{      NV17_CHANNEL_DMA     , 0 },
06db7fded6dec8 Ben Skeggs          2022-06-01  268  		{      NV10_CHANNEL_DMA     , 0 },
06db7fded6dec8 Ben Skeggs          2022-06-01  269  		{      NV03_CHANNEL_DMA     , 0 },
06db7fded6dec8 Ben Skeggs          2022-06-01  270  		{}
06db7fded6dec8 Ben Skeggs          2022-06-01  271  	};
e270b3665f8321 Gustavo A. R. Silva 2025-04-16  272  	DEFINE_RAW_FLEX(struct nvif_chan_v0, args, name, TASK_COMM_LEN + 16);
5cca41ac70e587 Ben Skeggs          2024-07-26  273  	struct nvif_device *device = &cli->device;
ebb945a94bba2c Ben Skeggs          2012-07-20  274  	struct nouveau_channel *chan;
06db7fded6dec8 Ben Skeggs          2022-06-01  275  	const u64 plength = 0x10000;
06db7fded6dec8 Ben Skeggs          2022-06-01  276  	const u64 ioffset = plength;
06db7fded6dec8 Ben Skeggs          2022-06-01  277  	const u64 ilength = 0x02000;
06db7fded6dec8 Ben Skeggs          2022-06-01  278  	int cid, ret;
06db7fded6dec8 Ben Skeggs          2022-06-01  279  	u64 size;
06db7fded6dec8 Ben Skeggs          2022-06-01  280  
06db7fded6dec8 Ben Skeggs          2022-06-01  281  	cid = nvif_mclass(&device->object, hosts);
06db7fded6dec8 Ben Skeggs          2022-06-01  282  	if (cid < 0)
06db7fded6dec8 Ben Skeggs          2022-06-01  283  		return cid;
06db7fded6dec8 Ben Skeggs          2022-06-01  284  
06db7fded6dec8 Ben Skeggs          2022-06-01  285  	if (hosts[cid].oclass < NV50_CHANNEL_GPFIFO)
06db7fded6dec8 Ben Skeggs          2022-06-01  286  		size = plength;
06db7fded6dec8 Ben Skeggs          2022-06-01  287  	else
06db7fded6dec8 Ben Skeggs          2022-06-01  288  		size = ioffset + ilength;
ebb945a94bba2c Ben Skeggs          2012-07-20  289  
ebb945a94bba2c Ben Skeggs          2012-07-20  290  	/* allocate dma push buffer */
5cca41ac70e587 Ben Skeggs          2024-07-26  291  	ret = nouveau_channel_prep(cli, size, &chan);
ebb945a94bba2c Ben Skeggs          2012-07-20  292  	*pchan = chan;
ebb945a94bba2c Ben Skeggs          2012-07-20  293  	if (ret)
ebb945a94bba2c Ben Skeggs          2012-07-20  294  		return ret;
ebb945a94bba2c Ben Skeggs          2012-07-20  295  
ebb945a94bba2c Ben Skeggs          2012-07-20  296  	/* create channel object */
e270b3665f8321 Gustavo A. R. Silva 2025-04-16  297  	args->version = 0;
e270b3665f8321 Gustavo A. R. Silva 2025-04-16  298  	args->namelen = __member_size(args->name);
e270b3665f8321 Gustavo A. R. Silva 2025-04-16  299  	args->runlist = __ffs64(runm);
e270b3665f8321 Gustavo A. R. Silva 2025-04-16  300  	args->runq = 0;
e270b3665f8321 Gustavo A. R. Silva 2025-04-16  301  	args->priv = priv;
e270b3665f8321 Gustavo A. R. Silva 2025-04-16  302  	args->devm = BIT(0);
06db7fded6dec8 Ben Skeggs          2022-06-01  303  	if (hosts[cid].oclass < NV50_CHANNEL_GPFIFO) {
e270b3665f8321 Gustavo A. R. Silva 2025-04-16  304  		args->vmm = 0;
e270b3665f8321 Gustavo A. R. Silva 2025-04-16  305  		args->ctxdma = nvif_handle(&chan->push.ctxdma);
e270b3665f8321 Gustavo A. R. Silva 2025-04-16  306  		args->offset = chan->push.addr;
e270b3665f8321 Gustavo A. R. Silva 2025-04-16  307  		args->length = 0;
bbf8906b2cad17 Ben Skeggs          2014-08-10  308  	} else {
e270b3665f8321 Gustavo A. R. Silva 2025-04-16  309  		args->vmm = nvif_handle(&chan->vmm->vmm.object);
06db7fded6dec8 Ben Skeggs          2022-06-01  310  		if (hosts[cid].oclass < FERMI_CHANNEL_GPFIFO)
e270b3665f8321 Gustavo A. R. Silva 2025-04-16  311  			args->ctxdma = nvif_handle(&chan->push.ctxdma);
06db7fded6dec8 Ben Skeggs          2022-06-01  312  		else
e270b3665f8321 Gustavo A. R. Silva 2025-04-16  313  			args->ctxdma = 0;
e270b3665f8321 Gustavo A. R. Silva 2025-04-16  314  		args->offset = ioffset + chan->push.addr;
e270b3665f8321 Gustavo A. R. Silva 2025-04-16  315  		args->length = ilength;
06db7fded6dec8 Ben Skeggs          2022-06-01  316  	}
e270b3665f8321 Gustavo A. R. Silva 2025-04-16  317  	args->huserd = 0;
e270b3665f8321 Gustavo A. R. Silva 2025-04-16  318  	args->ouserd = 0;
06db7fded6dec8 Ben Skeggs          2022-06-01  319  
06db7fded6dec8 Ben Skeggs          2022-06-01  320  	/* allocate userd */
06db7fded6dec8 Ben Skeggs          2022-06-01  321  	if (hosts[cid].oclass >= VOLTA_CHANNEL_GPFIFO_A) {
06db7fded6dec8 Ben Skeggs          2022-06-01  322  		ret = nvif_mem_ctor(&cli->mmu, "abi16ChanUSERD", NVIF_CLASS_MEM_GF100,
06db7fded6dec8 Ben Skeggs          2022-06-01  323  				    NVIF_MEM_VRAM | NVIF_MEM_COHERENT | NVIF_MEM_MAPPABLE,
06db7fded6dec8 Ben Skeggs          2022-06-01  324  				    0, PAGE_SIZE, NULL, 0, &chan->mem_userd);
06db7fded6dec8 Ben Skeggs          2022-06-01  325  		if (ret)
ebb945a94bba2c Ben Skeggs          2012-07-20  326  			return ret;
ebb945a94bba2c Ben Skeggs          2012-07-20  327  
e270b3665f8321 Gustavo A. R. Silva 2025-04-16  328  		args->huserd = nvif_handle(&chan->mem_userd.object);
e270b3665f8321 Gustavo A. R. Silva 2025-04-16  329  		args->ouserd = 0;
ebb945a94bba2c Ben Skeggs          2012-07-20  330  
06db7fded6dec8 Ben Skeggs          2022-06-01  331  		chan->userd = &chan->mem_userd.object;
06db7fded6dec8 Ben Skeggs          2022-06-01  332  	} else {
06db7fded6dec8 Ben Skeggs          2022-06-01  333  		chan->userd = &chan->user;
06db7fded6dec8 Ben Skeggs          2022-06-01  334  	}
ebb945a94bba2c Ben Skeggs          2012-07-20  335  
e270b3665f8321 Gustavo A. R. Silva 2025-04-16 @336  	snprintf(args->name, __member_size(args->name), "%s[%d]",
e270b3665f8321 Gustavo A. R. Silva 2025-04-16  337  		 current->comm, task_pid_nr(current));
ebb945a94bba2c Ben Skeggs          2012-07-20  338  
06db7fded6dec8 Ben Skeggs          2022-06-01  339  	ret = nvif_object_ctor(&device->object, "abi16ChanUser", 0, hosts[cid].oclass,
e270b3665f8321 Gustavo A. R. Silva 2025-04-16  340  			       args, __struct_size(args), &chan->user);
06db7fded6dec8 Ben Skeggs          2022-06-01  341  	if (ret) {
06db7fded6dec8 Ben Skeggs          2022-06-01  342  		nouveau_channel_del(pchan);
ebb945a94bba2c Ben Skeggs          2012-07-20  343  		return ret;
bbf8906b2cad17 Ben Skeggs          2014-08-10  344  	}
ebb945a94bba2c Ben Skeggs          2012-07-20  345  
e270b3665f8321 Gustavo A. R. Silva 2025-04-16  346  	chan->runlist = args->runlist;
e270b3665f8321 Gustavo A. R. Silva 2025-04-16  347  	chan->chid = args->chid;
e270b3665f8321 Gustavo A. R. Silva 2025-04-16  348  	chan->inst = args->inst;
e270b3665f8321 Gustavo A. R. Silva 2025-04-16  349  	chan->token = args->token;
06db7fded6dec8 Ben Skeggs          2022-06-01  350  	return 0;
ebb945a94bba2c Ben Skeggs          2012-07-20  351  }
ebb945a94bba2c Ben Skeggs          2012-07-20  352  

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
Re: [PATCH v6 3/3] include: Set tsk->comm length to 64 bytes
Posted by Kees Cook 6 months, 2 weeks ago 
On Thu, Jul 24, 2025 at 06:06:12PM +0530, Bhupesh wrote:
> 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';	\

strscpy_pad() will already make sure buf is NUL-terminated, so I don't
see why there is a need for explicit final byte termination? (And even
if we do need it, then it should just be buf[sizeof(buf) - 1] otherwise
using a buf that is < TASK_COMM_EXT_LEN but > TASK_COMM_LEN will have
a spurious NUL byte write beyond its buffer.)

-- 
Kees Cook

Patchew 2.1-devel-b67e4c2

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