lock_parent() needs to recheck if dentry got __dentry_kill'ed under it

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commit 3b82140963 upstream.

In case when dentry passed to lock_parent() is protected from freeing only
by the fact that it's on a shrink list and trylock of parent fails, we
could get hit by __dentry_kill() (and subsequent dentry_kill(parent))
between unlocking dentry and locking presumed parent.  We need to recheck
that dentry is alive once we lock both it and parent *and* postpone
rcu_read_unlock() until after that point.  Otherwise we could return
a pointer to struct dentry that already is rcu-scheduled for freeing, with
->d_lock held on it; caller's subsequent attempt to unlock it can end
up with memory corruption.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

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Al Viro 2018-02-23 20:47:17 -05:00 • committed by Ben Hutchings

parent 4eb6a29b25

commit 8027915847

1 changed files with 8 additions and 3 deletions

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fs/dcache.c

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