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

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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>
This commit is contained in:
David Rientjes 2013-04-30 15:28:18 -07:00 committed by Linus Torvalds
parent dc7ee2aac8
commit 830e0fc967
1 changed files with 2 additions and 3 deletions
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5
fs/proc/base.c
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@ -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);