Messages in this thread Patch in this message | | | Date | Mon, 8 Apr 2013 18:55:13 -0700 (PDT) | From | David Rientjes <> | Subject | [patch] fs, proc: truncate /proc/pid/comm writes to first TASK_COMM_LEN bytes |
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Currently, a write to /proc/pid/write will return the number of bytes successfully written. If the actual string is greater than this, the remainder of the string will normally be written.
This results in things such as
$ echo -n "abcdefghijklmnopqrs" > /proc/self/comm
to result 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> --- fs/proc/base.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/fs/proc/base.c b/fs/proc/base.c --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -1347,11 +1347,10 @@ 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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