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vfs: fsmount: add missing mntget()

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sys_fsmount() needs to take a reference to the new mount when adding it
to the anonymous mount namespace.  Otherwise the filesystem can be
unmounted while it's still in use, as found by syzkaller.

Reported-by: Mark Rutland <mark.rutland@arm.com>
Reported-by: syzbot+99de05d099a170867f22@syzkaller.appspotmail.com
Reported-by: syzbot+7008b8b8ba7df475fdc8@syzkaller.appspotmail.com
Fixes: 93766fbd26 ("vfs: syscall: Add fsmount() to create a mount for a superblock")
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Eric Biggers 2019-06-12 11:43:13 -07:00 committed by Al Viro
parent 9e0babf2c0
commit 1b0b9cc8d3
1 changed files with 1 additions and 0 deletions
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fs/namespace.c
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@ -3445,6 +3445,7 @@ SYSCALL_DEFINE3(fsmount, int, fs_fd, unsigned int, flags,
ns->root = mnt; ns->root = mnt;
ns->mounts = 1; ns->mounts = 1;
list_add(&mnt->mnt_list, &ns->list); list_add(&mnt->mnt_list, &ns->list);
mntget(newmount.mnt);
/* Attach to an apparent O_PATH fd with a note that we need to unmount /* Attach to an apparent O_PATH fd with a note that we need to unmount
* it, not just simply put it. * it, not just simply put it.