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authorMiles Chen <miles.chen@mediatek.com>2019-09-12 13:34:52 +0300
committerIngo Molnar <mingo@kernel.org>2019-09-13 08:49:28 +0300
commit4adcdcea717cb2d8436bef00dd689aa5bc76f11b (patch)
tree4c009a87ab0a147025002f30e70a9bea8490a6c9 /kernel
parenteb92692b2544d3f415887dbbc98499843dfe568b (diff)
downloadlinux-4adcdcea717cb2d8436bef00dd689aa5bc76f11b.tar.xz
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' */ 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@mediatek.com> Cc: <linux-mediatek@lists.infradead.org> Cc: <wsd_upstream@mediatek.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: https://lkml.kernel.org/r/20190912103452.13281-1-miles.chen@mediatek.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/sched/psi.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 7acc632c3b82..4b14a3208fbe 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -1190,7 +1190,7 @@ 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;