On 16/11/06, Jesper Juhl <jesper.juhl@xxxxxxxxx> wrote:
On 16/11/06, David Chinner <dgc@xxxxxxx> wrote:
> On Thu, Nov 16, 2006 at 10:18:26PM +0100, Jesper Juhl wrote:
> > (got no reply on this when I originally send it on 20061031, so resending
> > now that a bit of time has passed. The patch still applies cleanly to
> > Linus' git tree as of today.)
> >
> >
> > The Coverity checker spotted a potential problem in XFS.
> >
> > The problem is that if, in xfs_mount(), this code triggers:
> >
> > ...
> > if (!mp->m_logdev_targp)
> > goto error0;
> > ...
> >
> > Then we'll end up calling xfs_unmountfs_close() with a NULL
> > 'mp->m_logdev_targp'.
> > This in turn will result in a call to xfs_free_buftarg() with its 'btp'
> > argument == NULL. xfs_free_buftarg() dereferences 'btp' leading to
> > a NULL pointer dereference and crash.
>
> Interesting that coverity found that, but failed to find the other
> leaks in that function from exactly the same code and error
> case.....
>
> > I think this can happen, since the fatal call to xfs_free_buftarg()
> > happens when 'm_logdev_targp != m_ddev_targp' and due to a check of
> > 'm_ddev_targp' against NULL in xfs_mount() (and subsequent return if it is
> > NULL) the two will never both be NULL when we hit the error0 label from
> > the two lines cited above.
> >
> > Comments welcome (please keep me on Cc: on replies).
> >
> > Here's a proposed patch to fix this by testing 'btp' against NULL in
> > xfs_free_buftarg().
>
> Not the right fix - we should only be trying to free valid
> buftargs, which means xfs_unmountfs_close() is the correct
> place to fix this....
>
Ok.
> e.g:
>
> - if (mp->m_logdev_targp != mp->m_ddev_targp)
> + if (mp->m_logdev_targp && (mp->m_logdev_targp != mp->m_ddev_targp))
>
> As to the afore-mentioned leaks, if we fail to allocate a realtime
> buftarg, then we will leak a reference to both the rtdev and logdev,
> and if we fail to allocate an external log buftarg we'll leak a
> reference to the logdev. i.e., we fail to do one or both of:
>
> xfs_blkdev_put(logdev);
> xfs_blkdev_put(rtdev);
>
> To remove the bdev references we may have gained earlier. Normally,
> these references are released by xfs_free_buftarg(), but because we
> failed to allocate the buftarg, we can't drop the references via
> that method....
>
How about something like the attached patch ?
(sorry about the attachment, but I can't inline the patch from my
current location - a whitespace damaged version is below though for
easy review)
Signed-off-by: Jesper Juhl <jesper.juhl@xxxxxxxxx>
---
fs/xfs/xfs_mount.c | 2 +-
fs/xfs/xfs_vfsops.c | 10 ++++++++--
2 files changed, 9 insertions(+), 3 deletions(-)
diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
index 9dfae18..3497128 100644
--- a/fs/xfs/xfs_mount.c
+++ b/fs/xfs/xfs_mount.c
@@ -1135,7 +1135,7 @@ #endif
void
xfs_unmountfs_close(xfs_mount_t *mp, struct cred *cr)
{
- if (mp->m_logdev_targp != mp->m_ddev_targp)
+ if (mp->m_logdev_targp && mp->m_logdev_targp != mp->m_ddev_targp)
xfs_free_buftarg(mp->m_logdev_targp, 1);
if (mp->m_rtdev_targp)
xfs_free_buftarg(mp->m_rtdev_targp, 1);
diff --git a/fs/xfs/xfs_vfsops.c b/fs/xfs/xfs_vfsops.c
index 62336a4..6d7e8f1 100644
--- a/fs/xfs/xfs_vfsops.c
+++ b/fs/xfs/xfs_vfsops.c
@@ -473,13 +473,19 @@ xfs_mount(
}
if (rtdev) {
mp->m_rtdev_targp = xfs_alloc_buftarg(rtdev, 1);
- if (!mp->m_rtdev_targp)
+ if (!mp->m_rtdev_targp) {
+ xfs_blkdev_put(logdev);
+ xfs_blkdev_put(rtdev);
goto error0;
+ }
}
mp->m_logdev_targp = (logdev && logdev != ddev) ?
xfs_alloc_buftarg(logdev, 1) : mp->m_ddev_targp;
- if (!mp->m_logdev_targp)
+ if (!mp->m_logdev_targp) {
+ xfs_blkdev_put(logdev);
+ xfs_blkdev_put(rtdev);
goto error0;
+ }
/*
* Setup flags based on mount(2) options and then the superblock
--
Jesper Juhl <jesper.juhl@xxxxxxxxx>
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patch.txt
Description: Text document
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