Commit 3756f640 authored Dec 14, 2017 by Arnd Bergmann Committed by Linus Torvalds Dec 14, 2017

exec: avoid gcc-8 warning for get_task_comm

gcc-8 warns about using strncpy() with the source size as the limit:

  fs/exec.c:1223:32: error: argument to 'sizeof' in 'strncpy' call is the same expression as the source; did you mean to use the size of the destination? [-Werror=sizeof-pointer-memaccess]

This is indeed slightly suspicious, as it protects us from source
arguments without NUL-termination, but does not guarantee that the
destination is terminated.

This keeps the strncpy() to ensure we have properly padded target
buffer, but ensures that we use the correct length, by passing the
actual length of the destination buffer as well as adding a build-time
check to ensure it is exactly TASK_COMM_LEN.

There are only 23 callsites which I all reviewed to ensure this is
currently the case.  We could get away with doing only the check or
passing the right length, but it doesn't hurt to do both.

Link: http://lkml.kernel.org/r/20171205151724.1764896-1-arnd@arndb.de


Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Suggested-by: Kees Cook <keescook@chromium.org>
Acked-by: Kees Cook <keescook@chromium.org>
Acked-by: Ingo Molnar <mingo@kernel.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Serge Hallyn <serge@hallyn.com>
Cc: James Morris <james.l.morris@oracle.com>
Cc: Aleksa Sarai <asarai@suse.de>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Frederic Weisbecker <frederic@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 302ec300

fs/exec.c

+3 −4

Original line number	Diff line number	Diff line
		@@ -1216,15 +1216,14 @@ killed:
		return -EAGAIN;
		}

		char get_task_comm(char buf, struct task_struct *tsk)
		char __get_task_comm(char buf, size_t buf_size, struct task_struct *tsk)
		{
		/* buf must be at least sizeof(tsk->comm) in size */
		task_lock(tsk);
		strncpy(buf, tsk->comm, sizeof(tsk->comm));
		strncpy(buf, tsk->comm, buf_size);
		task_unlock(tsk);
		return buf;
		}
		EXPORT_SYMBOL_GPL(get_task_comm);
		EXPORT_SYMBOL_GPL(__get_task_comm);

		/*
		* These functions flushes out all traces of the currently running executable

include/linux/sched.h

+5 −1

Original line number	Diff line number	Diff line
		@@ -1503,7 +1503,11 @@ static inline void set_task_comm(struct task_struct tsk, const char from)
		__set_task_comm(tsk, from, false);
		}

		extern char get_task_comm(char to, struct task_struct *tsk);
		extern char __get_task_comm(char to, size_t len, struct task_struct *tsk);
		#define get_task_comm(buf, tsk) ({ \
		BUILD_BUG_ON(sizeof(buf) != TASK_COMM_LEN); \
		__get_task_comm(buf, sizeof(buf), tsk); \
		})

		#ifdef CONFIG_SMP
		void scheduler_ipi(void);

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