[PATCH 4.19 131/142] initramfs: clean old path before creating a hardlink

Greg Kroah-Hartman
2018-12-14T12:06:39Z

[ Upstream commit 7c0950d455d6ab610d2990a13120f935b75abf2c ]

sys_link() can fail due to the new path already existing. This case
ofen occurs when we use a concated initrd, for example:

1) prepare a basic rootfs, it contains a regular files rc.local
lizhijian@:~/yocto-tiny-i386-2016-04-22$ cat etc/rc.local
#!/bin/sh
echo "Running /etc/rc.local..."
yocto-tiny-i386-2016-04-22$ find . | sed 's,^\./,,' | cpio -o -H newc | gzip -n -9 >../rootfs.cgz

2) create a extra initrd which also includes a etc/rc.local
lizhijian@:~/lkp-x86_64/etc$ echo "append initrd" >rc.local
lizhijian@:~/lkp/lkp-x86_64/etc$ cat rc.local
append initrd
lizhijian@:~/lkp/lkp-x86_64/etc$ ln rc.local rc.local.hardlink
append initrd
lizhijian@:~/lkp/lkp-x86_64/etc$ stat rc.local rc.local.hardlink
File: 'rc.local'
Size: 14 Blocks: 8 IO Block: 4096 regular file
Device: 801h/2049d Inode: 11296086 Links: 2
Access: (0664/-rw-rw-r--) Uid: ( 1002/lizhijian) Gid: ( 1002/lizhijian)
Access: 2018-11-15 16:08:28.654464815 +0800
Modify: 2018-11-15 16:07:57.514903210 +0800
Change: 2018-11-15 16:08:24.180228872 +0800
Birth: -
File: 'rc.local.hardlink'
Size: 14 Blocks: 8 IO Block: 4096 regular file
Device: 801h/2049d Inode: 11296086 Links: 2
Access: (0664/-rw-rw-r--) Uid: ( 1002/lizhijian) Gid: ( 1002/lizhijian)
Access: 2018-11-15 16:08:28.654464815 +0800
Modify: 2018-11-15 16:07:57.514903210 +0800
Change: 2018-11-15 16:08:24.180228872 +0800
Birth: -

lizhijian@:~/lkp/lkp-x86_64$ find . | sed 's,^\./,,' | cpio -o -H newc | gzip -n -9 >../rc-local.cgz
lizhijian@:~/lkp/lkp-x86_64$ gzip -dc ../rc-local.cgz | cpio -t
.
etc
etc/rc.local.hardlink <<< it will be extracted first at this initrd
etc/rc.local

3) concate 2 initrds and boot
lizhijian@:~/lkp$ cat rootfs.cgz rc-local.cgz >concate-initrd.cgz
lizhijian@:~/lkp$ qemu-system-x86_64 -nographic -enable-kvm -cpu host -smp 1 -m 1024 -kernel ~/lkp/linux/arch/x86/boot/bzImage -append "console=ttyS0 earlyprint=ttyS0 ignore_loglevel" -initrd ./concate-initr.cgz -serial stdio -nodefaults

In this case, sys_link(2) will fail and return -EEXIST, so we can only get
the rc.local at rootfs.cgz instead of rc-local.cgz

[akpm@linux-foundation.org: move code to avoid forward declaration]
Link: http://lkml.kernel.org/r/1542352368-13299-1-git-send-email-lizhijian@cn.fujitsu.com
Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
Cc: Philip Li <philip.li@intel.com>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Cc: Li Zhijian <zhijianx.li@intel.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
init/initramfs.c | 22 ++++++++++++----------
1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/init/initramfs.c b/init/initramfs.c
index 640557788026..f6f4a1e4cd54 100644
--- a/init/initramfs.c
+++ b/init/initramfs.c
@@ -291,16 +291,6 @@ static int __init do_reset(void)
return 1;
}

-static int __init maybe_link(void)
-{
- if (nlink >= 2) {
- char *old = find_link(major, minor, ino, mode, collected);
- if (old)
- return (ksys_link(old, collected) < 0) ? -1 : 1;
- }
- return 0;
-}
-
static void __init clean_path(char *path, umode_t fmode)
{
struct kstat st;
@@ -313,6 +303,18 @@ static void __init clean_path(char *path, umode_t fmode)
}
}

+static int __init maybe_link(void)
+{
+ if (nlink >= 2) {
+ char *old = find_link(major, minor, ino, mode, collected);
+ if (old) {
+ clean_path(collected, 0);
+ return (ksys_link(old, collected) < 0) ? -1 : 1;
+ }
+ }
+ return 0;
+}
+
static __initdata int wfd;

static int __init do_name(void)
--
2.19.1