| Message ID | 20190912103452.13281-1-miles.chen@mediatek.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | psi: put NULL char correctly in psi_write() | expand |
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@mediatek.com> > AuthorDate: Thu, 12 Sep 2019 18:34:52 +08:00 > Committer: Ingo Molnar <mingo@kernel.org> > 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)
diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c index 6e52b67b420e..517e3719027e 100644 --- a/kernel/sched/psi.c +++ b/kernel/sched/psi.c @@ -1198,7 +1198,7 @@ static ssize_t psi_write(struct file *file, const char __user *user_buf, if (static_branch_likely(&psi_disabled)) return -EOPNOTSUPP; - buf_size = min(nbytes, (sizeof(buf) - 1)); + buf_size = min(nbytes, sizeof(buf)); if (copy_from_user(buf, user_buf, buf_size)) return -EFAULT;
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' */ Before: %cd /proc/pressure/ %echo "123456789|123456789|123456789|1234" > memory [ 22.473497] nbytes=35,buf_size=31 [ 22.473775] 123456789|123456789|123456789| (print 30 chars) %sh: write error: Invalid argument %echo "123456789|123456789|123456789|1" > memory [ 64.916162] nbytes=32,buf_size=31 [ 64.916331] 123456789|123456789|123456789| (print 30 chars) %sh: write error: Invalid argument After: %cd /proc/pressure/ %echo "123456789|123456789|123456789|1234" > memory [ 254.837863] nbytes=35,buf_size=32 [ 254.838541] 123456789|123456789|123456789|1 (print 31 chars) %sh: write error: Invalid argument %echo "123456789|123456789|123456789|1" > memory [ 9965.714935] nbytes=32,buf_size=32 [ 9965.715096] 123456789|123456789|123456789|1 (print 31 chars) %sh: write error: Invalid argument Signed-off-by: Miles Chen <miles.chen@mediatek.com> --- kernel/sched/psi.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)