Commit 97242f99 authored Aug 01, 2015 by Al Viro

link_path_walk(): be careful when failing with ENOTDIR



In RCU mode we might end up with dentry evicted just we check
that it's a directory.  In such case we should return ECHILD
rather than ENOTDIR, so that pathwalk would be retries in non-RCU
mode.

Breakage had been introduced in commit b18825a7 - prior to that
we were looking at nd->inode, which had been fetched before
verifying that ->d_seq was still valid.  That form of check
would only be satisfied if at some point the pathname prefix
would indeed have resolved to a non-directory.  The fix consists
of checking ->d_seq after we'd run into a non-directory dentry,
and failing with ECHILD in case of mismatch.

Note that all branches since 3.12 have that problem...

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

parent cbfe8fa6

fs/namei.c

+6 −1

Original line number	Diff line number	Diff line
		@@ -1954,10 +1954,15 @@ OK:
		continue;
		}
		}
		if (unlikely(!d_can_lookup(nd->path.dentry)))
		if (unlikely(!d_can_lookup(nd->path.dentry))) {
		if (nd->flags & LOOKUP_RCU) {
		if (unlazy_walk(nd, NULL, 0))
		return -ECHILD;
		}
		return -ENOTDIR;
		}
		}
		}

		static const char path_init(struct nameidata nd, unsigned flags)
		{

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