psi: put NULL char correctly in psi_write()
Subsystems (3)
PATCH 1/1 psi: put NULL char correctly in psi_write()
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
--- kernel/sched/psi.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
kernel/sched/psi.c +1 -1
@@ -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 ;
Signature · 1 line
2.18.0
[tip: sched/core] sched/psi: Correct overly pessimistic size calculation
The following commit has been merged into the sched/core branch of tip:
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 <[email protected]> AuthorDate: Thu, 12 Sep 2019 18:34:52 +08:00 Committer: Ingo Molnar <[email protected]> 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' */
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.
--- kernel/sched/psi.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
kernel/sched/psi.c +1 -1
@@ -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 ;
RE: [tip: sched/core] sched/psi: Correct overly pessimistic size calculation
From: Miles Chen
Quoted 23 lines
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 <[email protected]> AuthorDate: Thu, 12 Sep 2019 18:34:52 +08:00 Committer: Ingo Molnar <[email protected]> CommitterDate: Fri, 13 Sep 2019 07:49:28 +02:00sched/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.
Quoted 8 lines
/* 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
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