From: Miles Chen > Sent: 13 September 2019 23:43 > The following commit has been merged into the sched/core branch of tip: > > Commit-ID: 4adcdcea717cb2d8436bef00dd689aa5bc76f11b > Gitweb: https://git.kernel.org/tip/4adcdcea717cb2d8436bef00dd689aa5bc76f11b > Author: Miles Chen <miles.chen@xxxxxxxxxxxx> > AuthorDate: Thu, 12 Sep 2019 18:34:52 +08:00 > Committer: Ingo Molnar <mingo@xxxxxxxxxx> > CommitterDate: Fri, 13 Sep 2019 07:49:28 +02:00 > > sched/psi: Correct overly pessimistic size calculation > > When passing a equal or more then 32 bytes long string to psi_write(), > psi_write() copies 31 bytes to its buf and overwrites buf[30] > with '\0'. Which makes the input string 1 byte shorter than > it should be. > > Fix it by copying sizeof(buf) bytes when nbytes >= sizeof(buf). > > This does not cause problems in normal use case like: > "some 500000 10000000" or "full 500000 10000000" because they > are less than 32 bytes in length. > > /* assuming nbytes == 35 */ > char buf[32]; > > buf_size = min(nbytes, (sizeof(buf) - 1)); /* buf_size = 31 */ > if (copy_from_user(buf, user_buf, buf_size)) > return -EFAULT; > > buf[buf_size - 1] = '\0'; /* buf[30] = '\0' */ Wouldn't it be better to also allow the user to pass an unterminated string? So leave the '-1' on the assignment to buf_size, but remove it from the last line. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
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