Hi, Back in 2006 (2006-10-31 to be specific, reposted on 2006-11-16), I submitted a patch to fix a potential NULL pointer deref in XFS on failed mount.
The patch drew some comments and it turned out that my initial approach to a fix was wrong. David Chinner kindly offered some tips on how to implement a proper fix, and on 2006-11-20 I submitted a revised fix. This patch, unfortunately, didn't draw any comments, nor did it ever get merged anywhere. I believe that now sufficient time has passed to warrent a repost ;-) The Coverity checker spotted (as bug #346) 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. 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. This patch fixes the issue by checking mp->m_logdev_targp against NULL in xfs_unmountfs_close() and doing the proper xfs_blkdev_put(logdev); and xfs_blkdev_put(rtdev); on (!mp->m_rtdev_targp) in xfs_mount(). Compile tested. Comments and feedback welcome. Please consider merging. Signed-off-by: Jesper Juhl <[EMAIL PROTECTED]> --- 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 a96bde6..dfe45c3 100644 --- a/fs/xfs/xfs_mount.c +++ b/fs/xfs/xfs_mount.c @@ -1132,7 +1132,7 @@ xfs_unmountfs(xfs_mount_t *mp, struct cred *cr) 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 65c5612..92fd965 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 (Please keep me on Cc when replying) -- Jesper Juhl <[EMAIL PROTECTED]> Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html Plain text mails only, please http://www.expita.com/nomime.html - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/