From 0b2d71a7c82628bb36fd43e80193bcc2693c239a Mon Sep 17 00:00:00 2001 From: "Adrian Huang (Lenovo)" Date: Thu, 14 Aug 2025 17:44:53 +0800 Subject: [PATCH] pidfs: Fix memory leak in pidfd_info() After running the program 'ioctl_pidfd03' of Linux Test Project (LTP) or the program 'pidfd_info_test' in 'tools/testing/selftests/pidfd' of the kernel source, kmemleak reports the following memory leaks: # cat /sys/kernel/debug/kmemleak unreferenced object 0xff110020e5988000 (size 8216): comm "ioctl_pidfd03", pid 10853, jiffies 4294800031 hex dump (first 32 bytes): 02 40 00 00 00 00 00 00 10 00 00 00 00 00 00 00 .@.............. 00 00 00 00 af 01 00 00 80 00 00 00 00 00 00 00 ................ backtrace (crc 69483047): kmem_cache_alloc_node_noprof+0x2fb/0x410 copy_process+0x178/0x1740 kernel_clone+0x99/0x3b0 __do_sys_clone3+0xbe/0x100 do_syscall_64+0x7b/0x2c0 entry_SYSCALL_64_after_hwframe+0x76/0x7e ... unreferenced object 0xff11002097b70000 (size 8216): comm "pidfd_info_test", pid 11840, jiffies 4294889165 hex dump (first 32 bytes): 06 40 00 00 00 00 00 00 10 00 00 00 00 00 00 00 .@.............. 00 00 00 00 b5 00 00 00 80 00 00 00 00 00 00 00 ................ backtrace (crc a6286bb7): kmem_cache_alloc_node_noprof+0x2fb/0x410 copy_process+0x178/0x1740 kernel_clone+0x99/0x3b0 __do_sys_clone3+0xbe/0x100 do_syscall_64+0x7b/0x2c0 entry_SYSCALL_64_after_hwframe+0x76/0x7e ... The leak occurs because pidfd_info() obtains a task_struct via get_pid_task() but never calls put_task_struct() to drop the reference, leaving task->usage unbalanced. Fix the issue by adding '__free(put_task) = NULL' to the local variable 'task', ensuring that put_task_struct() is automatically invoked when the variable goes out of scope. Fixes: 7477d7dce48a ("pidfs: allow to retrieve exit information") Signed-off-by: Adrian Huang (Lenovo) Link: https://lore.kernel.org/20250814094453.15232-1-adrianhuang0701@gmail.com Signed-off-by: Christian Brauner --- fs/pidfs.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/pidfs.c b/fs/pidfs.c index edc35522d75c..108e7527f837 100644 --- a/fs/pidfs.c +++ b/fs/pidfs.c @@ -296,12 +296,12 @@ static __u32 pidfs_coredump_mask(unsigned long mm_flags) static long pidfd_info(struct file *file, unsigned int cmd, unsigned long arg) { struct pidfd_info __user *uinfo = (struct pidfd_info __user *)arg; + struct task_struct *task __free(put_task) = NULL; struct pid *pid = pidfd_pid(file); size_t usize = _IOC_SIZE(cmd); struct pidfd_info kinfo = {}; struct pidfs_exit_info *exit_info; struct user_namespace *user_ns; - struct task_struct *task; struct pidfs_attr *attr; const struct cred *c; __u64 mask; -- 2.25.1