From: Miles Chen <miles.chen@xxxxxxxxxxxx> [ Upstream commit 4adcdcea717cb2d8436bef00dd689aa5bc76f11b ] 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 Also remove the superfluous parentheses. Signed-off-by: Miles Chen <miles.chen@xxxxxxxxxxxx> Cc: <linux-mediatek@xxxxxxxxxxxxxxxxxxx> Cc: <wsd_upstream@xxxxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Link: https://lkml.kernel.org/r/20190912103452.13281-1-miles.chen@xxxxxxxxxxxx Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- kernel/sched/psi.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c index 6e52b67b420e7..517e3719027e6 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; -- 2.20.1
