Commit 830e0fc9 authored Apr 30, 2013 by David Rientjes Committed by Linus Torvalds Apr 30, 2013

fs, proc: truncate /proc/pid/comm writes to first TASK_COMM_LEN bytes



Currently, a write to a procfs file will return the number of bytes
successfully written.  If the actual string is longer than this, the
remainder of the string will not be be written and userspace will
complete the operation by issuing additional write()s.

Hence

	$ echo -n "abcdefghijklmnopqrs" > /proc/self/comm

results in

	$ cat /proc/$$/comm
	pqrs

since the final four bytes were written with a second write() since
TASK_COMM_LEN == 16.  This is obviously an undesired result and not
equivalent to prctl(PR_SET_NAME).  The implementation should not need to
know the definition of TASK_COMM_LEN.

This patch truncates the string to the first TASK_COMM_LEN bytes and
returns the bytes written as the length of the string written so the
second write() is suppressed.

	$ cat /proc/$$/comm
	abcdefghijklmno

Signed-off-by: David Rientjes <rientjes@google.com>
Acked-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent dc7ee2aa

fs/proc/base.c

+2 −3

Original line number	Diff line number	Diff line
		@@ -1348,11 +1348,10 @@ static ssize_t comm_write(struct file file, const char __user buf,
		struct inode *inode = file_inode(file);
		struct task_struct *p;
		char buffer[TASK_COMM_LEN];
		const size_t maxlen = sizeof(buffer) - 1;

		memset(buffer, 0, sizeof(buffer));
		if (count > sizeof(buffer) - 1)
		count = sizeof(buffer) - 1;
		if (copy_from_user(buffer, buf, count))
		if (copy_from_user(buffer, buf, count > maxlen ? maxlen : count))
		return -EFAULT;

		p = get_proc_task(inode);

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