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Subject[PATCH] pidfd: fix memory leak in pidfd_getfd()
kmemleak backtrace:

comm "pidfd_getfd_tes", pid 1406, jiffies 4294936898 (age 8.644s)
hex dump (first 32 bytes):
00 00 00 00 00 00 00 00 90 da d8 f6 80 d5 6f f2 ..............o.
b8 fb 9b ea c0 91 99 d1 00 00 00 00 00 00 00 00 ................
backtrace:
[<8da987ad>] kmem_cache_alloc+0x199/0x4c0
[<8ff6a575>] __alloc_file+0x1e/0xe0
[<e1479798>] alloc_empty_file+0x45/0x100
[<727fe6eb>] alloc_file+0x23/0xf0
[<457148ef>] alloc_file_pseudo+0x98/0x100
[<c104ed3d>] __shmem_file_setup.part.67+0x66/0x120
[<5edc3e9b>] shmem_file_setup+0x4c/0x70
[<9c446684>] __ia32_sys_memfd_create+0x122/0x1c0
[<e129fc9c>] do_syscall_32_irqs_on+0x3d/0x260
[<62569441>] do_fast_syscall_32+0x39/0xb0
[<3c515b7e>] do_SYSENTER_32+0x15/0x20
[<69819a3a>] entry_SYSENTER_32+0xa9/0xfc

comm "pidfd_getfd_tes", pid 1406, jiffies 4294936898 (age 8.644s)
hex dump (first 16 bytes):
01 00 00 00 01 00 00 00 00 00 00 00 00 00 00 00 ................
backtrace:
[<8da987ad>] kmem_cache_alloc+0x199/0x4c0
[<b67faec5>] security_file_alloc+0x20/0x90
[<ed849d41>] __alloc_file+0x40/0xe0
[<e1479798>] alloc_empty_file+0x45/0x100
[<727fe6eb>] alloc_file+0x23/0xf0
[<457148ef>] alloc_file_pseudo+0x98/0x100
[<c104ed3d>] __shmem_file_setup.part.67+0x66/0x120
[<5edc3e9b>] shmem_file_setup+0x4c/0x70
[<9c446684>] __ia32_sys_memfd_create+0x122/0x1c0
[<e129fc9c>] do_syscall_32_irqs_on+0x3d/0x260
[<62569441>] do_fast_syscall_32+0x39/0xb0
[<3c515b7e>] do_SYSENTER_32+0x15/0x20
[<69819a3a>] entry_SYSENTER_32+0xa9/0xfc

This is because in pidfd_getfd(), the file->f_count is incremented twice
1) __pidfd_fget() gets file ref by incrementing f_count in __fget_files()
2) f_count is incremented While installing fd in __fd_install_received()
i.e. get_file().

Memory leak occurs because the refs count do not match, the struct file
object is never freed.

Secondly the error validity check (ret < 0) after the call to
fd_install_received() is not needed since this function cannot return
negative number after incrementing f_count. So it is wrong to call fput
on condition (ret < 0).

Change pidfd_getfd() to call fput() on file reference once its installed
as new_fd in target process.

Signed-off-by: Vamshi K Sthambamkadi <vamshi.k.sthambamkadi@gmail.com>
---
kernel/pid.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/pid.c b/kernel/pid.c
index 5799ae5..d00139c 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -653,8 +653,8 @@ static int pidfd_getfd(struct pid *pid, int fd)
return PTR_ERR(file);

ret = fd_install_received(file, O_CLOEXEC);
- if (ret < 0)
- fput(file);
+
+ fput(file);
return ret;
}

--
2.7.4
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