fs: call security_d_instantiate in d_obtain_alias V2
While trying to track down some NFS problems with BTRFS, I kept noticing I was getting -EACCESS for no apparent reason. Eric Paris and printk() helped me figure out that it was SELinux that was giving me grief, with the following denial type=AVC msg=audit(1290013638.413:95): avc: denied { 0x800000 } for pid=1772 comm="nfsd" name="" dev=sda1 ino=256 scontext=system_u:system_r:kernel_t:s0 tcontext=system_u:object_r:unlabeled_t:s0 tclass=file Turns out this is because in d_obtain_alias if we can't find an alias we create one and do all the normal instantiation stuff, but we don't do the security_d_instantiate. Usually we are protected from getting a hashed dentry that hasn't yet run security_d_instantiate() by the parent's i_mutex, but obviously this isn't an option there, so in order to deal with the case that a second thread comes in and finds our new dentry before we get to run security_d_instantiate(), we go ahead and call it if we find a dentry already. Eric assures me that this is ok as the code checks to see if the dentry has been initialized already so calling security_d_instantiate() against the same dentry multiple times is ok. With this patch I'm no longer getting errant -EACCESS values. Signed-off-by: Josef Bacik <josef@redhat.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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@ -1612,10 +1612,13 @@ struct dentry *d_obtain_alias(struct inode *inode)
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__bit_spin_unlock(0, (unsigned long *)&tmp->d_sb->s_anon.first);
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__bit_spin_unlock(0, (unsigned long *)&tmp->d_sb->s_anon.first);
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spin_unlock(&tmp->d_lock);
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spin_unlock(&tmp->d_lock);
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spin_unlock(&inode->i_lock);
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spin_unlock(&inode->i_lock);
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security_d_instantiate(tmp, inode);
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return tmp;
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return tmp;
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out_iput:
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out_iput:
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if (res && !IS_ERR(res))
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security_d_instantiate(res, inode);
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iput(inode);
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iput(inode);
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return res;
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return res;
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}
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}
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