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SubjectRe: [PATCH] vfs: Don't exchange filenames unconditionally.
On Thu, 18 Sep 2014 13:22:07 +0200 Mateusz Guzik wrote:
> On Thu, Sep 18, 2014 at 02:55:00PM +0400, Mikhail Efremov wrote:
> > Only exchange source and destination filenames
> > if flags contain RENAME_EXCHANGE.
>
> But names are still exchanged without RENAME_EXCHANGE, provided they are
> long enough.
>
> da1ce0670c14 introduced this behaviour also for short names and this is
> what you are reverting here.
>
> That said, I think the patch is fine as an interim change, but should
> note facts mentioned above.
>
> For more info please see https://lkml.org/lkml/2014/9/7/6

Thanks for pointing out that thread to me, I didn't read it before
sending the patch.

> I'll be posting a RFC patch for actual problem next week.

I suppose then that no sense to resend this patch right now, I'll just
wait the proper solution from you.
Yet this patch can be used as a temporary workaround (as you mentioned
above) if the proper solution takes longer than expected to implement.

> > In case if executable file was running and replaced by
> > other file /proc/PID/exe should still show correct file name,
> > not the old name of the file by which it was replaced.
>
>
>
>
> > The scenario when this bug manifests itself was like this:
> > * ALT Linux uses rpm and start-stop-daemon;
> > * during a package upgrade rpm creates a temporary file
> > for an executable to rename it upon successful unpacking;
> > * start-stop-daemon is run subsequently and it obtains
> > the (nonexistant) temporary filename via /proc/PID/exe
> > thus failing to identify the running process.
> >
> > Cc: Miklos Szeredi <mszeredi@suse.cz>
> > Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> > Cc: linux-fsdevel@vger.kernel.org
> >
> > Fixes: da1ce0670c14 "vfs: add cross-rename"
> > Signed-off-by: Mikhail Efremov <sem@altlinux.org>
> > ---
> > fs/dcache.c | 27 +++++++++++++++++++--------
> > 1 file changed, 19 insertions(+), 8 deletions(-)
> >
> > diff --git a/fs/dcache.c b/fs/dcache.c
> > index 7a5b514..3218570 100644
> > --- a/fs/dcache.c
> > +++ b/fs/dcache.c
> > @@ -2372,7 +2372,8 @@ void dentry_update_name_case(struct dentry *dentry, struct qstr *name)
> > }
> > EXPORT_SYMBOL(dentry_update_name_case);
> >
> > -static void switch_names(struct dentry *dentry, struct dentry *target)
> > +static void switch_names(struct dentry *dentry, struct dentry *target,
> > + bool exchange)
> > {
> > if (dname_external(target)) {
> > if (dname_external(dentry)) {
> > @@ -2404,11 +2405,21 @@ static void switch_names(struct dentry *dentry, struct dentry *target)
> > /*
> > * Both are internal.
> > */
> > - unsigned int i;
> > - BUILD_BUG_ON(!IS_ALIGNED(DNAME_INLINE_LEN, sizeof(long)));
> > - for (i = 0; i < DNAME_INLINE_LEN / sizeof(long); i++) {
> > - swap(((long *) &dentry->d_iname)[i],
> > - ((long *) &target->d_iname)[i]);
> > + if (exchange) {
> > + unsigned int i;
> > +
> > + BUILD_BUG_ON(!IS_ALIGNED(DNAME_INLINE_LEN,
> > + sizeof(long)));
> > + for (i = 0; i < DNAME_INLINE_LEN / sizeof(long);
> > + i++) {
> > + swap(((long *) &dentry->d_iname)[i],
> > + ((long *) &target->d_iname)[i]);
> > + }
> > + } else {
> > + memcpy(dentry->d_iname, target->d_name.name,
> > + target->d_name.len + 1);
> > + dentry->d_name.len = target->d_name.len;
> > + return;
> > }
> > }
> > }
> > @@ -2510,7 +2521,7 @@ static void __d_move(struct dentry *dentry, struct dentry *target,
> > list_del(&target->d_u.d_child);
> >
> > /* Switch the names.. */
> > - switch_names(dentry, target);
> > + switch_names(dentry, target, exchange);
> > swap(dentry->d_name.hash, target->d_name.hash);
> >
> > /* ... and switch the parents */
> > @@ -2649,7 +2660,7 @@ static void __d_materialise_dentry(struct dentry *dentry, struct dentry *anon)
> >
> > dparent = dentry->d_parent;
> >
> > - switch_names(dentry, anon);
> > + switch_names(dentry, anon, false);
> > swap(dentry->d_name.hash, anon->d_name.hash);
> >
> > dentry->d_parent = dentry;
> > --
> > 1.8.5.5
> >
> > --
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> > Please read the FAQ at http://www.tux.org/lkml/
>

--
WBR, Mikhail Efremov


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