title: kfence: fix memory leak when cat kfence objects
description: In the Linux kernel, the following vulnerability has been resolved:
kfence: fix memory leak when cat kfence objects
Hulk robot reported a kmemleak problem:
unreferenced object 0xffff93d1d8cc02e8 (size 248):
comm "cat", pid 23327, jiffies 4624670141 (age 495992.217s)
hex dump (first 32 bytes):
00 40 85 19 d4 93 ff ff 00 10 00 00 00 00 00 00  .@..............
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
backtrace:
seq_open+0x2a/0x80
full_proxy_open+0x167/0x1e0
do_dentry_open+0x1e1/0x3a0
path_openat+0x961/0xa20
do_filp_open+0xae/0x120
do_sys_openat2+0x216/0x2f0
do_sys_open+0x57/0x80
do_syscall_64+0x33/0x40
entry_SYSCALL_64_after_hwframe+0x44/0xa9
unreferenced object 0xffff93d419854000 (size 4096):
comm "cat", pid 23327, jiffies 4624670141 (age 495992.217s)
hex dump (first 32 bytes):
6b 66 65 6e 63 65 2d 23 32 35 30 3a 20 30 78 30  kfence-#250: 0x0
30 30 30 30 30 30 30 37 35 34 62 64 61 31 32 2d  0000000754bda12-
backtrace:
seq_read_iter+0x313/0x440
seq_read+0x14b/0x1a0
full_proxy_read+0x56/0x80
vfs_read+0xa5/0x1b0
ksys_read+0xa0/0xf0
do_syscall_64+0x33/0x40
entry_SYSCALL_64_after_hwframe+0x44/0xa9
I find that we can easily reproduce this problem with the following
commands:
cat /sys/kernel/debug/kfence/objects
echo scan > /sys/kernel/debug/kmemleak
cat /sys/kernel/debug/kmemleak
The leaked memory is allocated in the stack below:
do_syscall_64
do_sys_open
do_dentry_open
full_proxy_open
seq_open            ---> alloc seq_file
vfs_read
full_proxy_read
seq_read
seq_read_iter
traverse          ---> alloc seq_buf
And it should have been released in the following process:
do_syscall_64
syscall_exit_to_user_mode
exit_to_user_mode_prepare
task_work_run
____fput
__fput
full_proxy_release  ---> free here
However, the release function corresponding to file_operations is not
implemented in kfence.  As a result, a memory leak occurs.  Therefore,
the solution to this problem is to implement the corresponding release
function.
affected:
{
product: Linux
vendor: Linux
defaultStatus: unaffected
repo: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
versions:
version: 0ce20dd84089, lessThan: 2f06c8293d27, status: affected, versionType: git
version: 0ce20dd84089, lessThan: 0129ab1f268b, status: affected, versionType: git
}
{
product: Linux
vendor: Linux
defaultStatus: affected
repo: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
versions:
version: 5.12, status: affected
version: 0, lessThan: 5.12, status: unaffected, versionType: custom
version: 5.15.12, lessThanOrEqual: 5.15.*, status: unaffected, versionType: custom
version: 5.16, lessThanOrEqual: *, status: unaffected, versionType: original_commit_for_fix
}
