[PATCH v5 06/15] elfcore: make prpsinfo always get a nul terminated task comm

[Yafang Shao <laoar.shao@xxxxxxxxx>]

kernel test robot reported a -Wstringop-truncation warning after I
extend task comm from 16 to 24. Below is the detailed warning:

   fs/binfmt_elf.c: In function 'fill_psinfo.isra':
>> fs/binfmt_elf.c:1575:9: warning: 'strncpy' output may be truncated copying 16 bytes from a string of length 23 [-Wstringop-truncation]
    1575 |         strncpy(psinfo->pr_fname, p->comm, sizeof(psinfo->pr_fname));
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This patch can fix this warning.

struct elf_prpsinfo is used to dump the task information in userspace
coredump or kernel vmcore. Use TASK_COMM_LEN_16 instead of hard-coded 16
to make it more grepable, and use strscpy_pad() instead of strncpy() to
make it always get a nul terminated task comm.

Reported-by: kernel test robot <lkp@xxxxxxxxx>
Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Petr Mladek <pmladek@xxxxxxxx>
---
 fs/binfmt_elf.c                | 2 +-
 include/linux/elfcore-compat.h | 3 ++-
 include/linux/elfcore.h        | 4 ++--
 3 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index a813b70f594e..a4ba79fce2a9 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -1572,7 +1572,7 @@ static int fill_psinfo(struct elf_prpsinfo *psinfo, struct task_struct *p,
 	SET_UID(psinfo->pr_uid, from_kuid_munged(cred->user_ns, cred->uid));
 	SET_GID(psinfo->pr_gid, from_kgid_munged(cred->user_ns, cred->gid));
 	rcu_read_unlock();
-	strncpy(psinfo->pr_fname, p->comm, sizeof(psinfo->pr_fname));
+	strscpy_pad(psinfo->pr_fname, p->comm, sizeof(psinfo->pr_fname));
 
 	return 0;
 }
diff --git a/include/linux/elfcore-compat.h b/include/linux/elfcore-compat.h
index e272c3d452ce..69fa1a728964 100644
--- a/include/linux/elfcore-compat.h
+++ b/include/linux/elfcore-compat.h
@@ -5,6 +5,7 @@
 #include <linux/elf.h>
 #include <linux/elfcore.h>
 #include <linux/compat.h>
+#include <linux/sched.h>
 
 /*
  * Make sure these layouts match the linux/elfcore.h native definitions.
@@ -43,7 +44,7 @@ struct compat_elf_prpsinfo
 	__compat_uid_t			pr_uid;
 	__compat_gid_t			pr_gid;
 	compat_pid_t			pr_pid, pr_ppid, pr_pgrp, pr_sid;
-	char				pr_fname[16];
+	char				pr_fname[TASK_COMM_LEN_16];
 	char				pr_psargs[ELF_PRARGSZ];
 };
 
diff --git a/include/linux/elfcore.h b/include/linux/elfcore.h
index 2aaa15779d50..ee7ac09734ba 100644
--- a/include/linux/elfcore.h
+++ b/include/linux/elfcore.h
@@ -65,8 +65,8 @@ struct elf_prpsinfo
 	__kernel_gid_t	pr_gid;
 	pid_t	pr_pid, pr_ppid, pr_pgrp, pr_sid;
 	/* Lots missing */
-	char	pr_fname[16];	/* filename of executable */
-	char	pr_psargs[ELF_PRARGSZ];	/* initial part of arg list */
+	char	pr_fname[TASK_COMM_LEN_16];	/* filename of executable */
+	char	pr_psargs[ELF_PRARGSZ];		/* initial part of arg list */
 };
 
 static inline void elf_core_copy_regs(elf_gregset_t *elfregs, struct pt_regs *regs)
-- 
2.17.1