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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 b18825a - 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>
This commit is contained in:
Al Viro 2015-08-01 19:59:28 -04:00
parent cbfe8fa6cd
commit 97242f99a0
1 changed files with 6 additions and 1 deletions
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7
fs/namei.c
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@ -1954,8 +1954,13 @@ static int link_path_walk(const char *name, struct nameidata *nd)
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;
}
}
}