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vfs: remove unneeded permission check from path_init

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When path_init is called with a valid dfd, that code checks permissions
on the open directory fd and returns an error if the check fails. This
permission check is redundant, however.

Both callers of path_init immediately call link_path_walk afterward. The
first thing that link_path_walk does for pathnames that do not consist
only of slashes is to check for exec permissions at the starting point of
the path walk.  And this check in path_init() is on the path taken only
when *name != '/' && *name != '\0'.

In most cases, these checks are very quick, but when the dfd is for a
file on a NFS mount with the actimeo=0, each permission check goes
out onto the wire. The result is 2 identical ACCESS calls.

Given that these codepaths are fairly "hot", I think it makes sense to
eliminate the permission check in path_init and simply assume that the
caller will eventually check the permissions before proceeding.

Reported-by: Dave Wysochanski <dwysocha@redhat.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Jeff Layton 2012-12-11 08:56:16 -05:00 • committed by Al Viro
parent 1e75529e3c
commit 582aa64a04
1 changed files with 1 additions and 6 deletions
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7
fs/namei.c
View file

@ -1903,6 +1903,7 @@ static int path_init(int dfd, const char *name, unsigned int flags,
get_fs_pwd(current->fs, &nd->path);
}
} else {
/* Caller must check execute permissions on the starting path component */
struct fd f = fdget_raw(dfd);
struct dentry *dentry;
@ -1916,12 +1917,6 @@ static int path_init(int dfd, const char *name, unsigned int flags,
fdput(f);
return -ENOTDIR;
}
retval = inode_permission(dentry->d_inode, MAY_EXEC);
if (retval) {
fdput(f);
return retval;
}
}
nd->path = f.file->f_path;