lkml.org 
[lkml]   [2020]   [May]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH v4.4] xfs: validate cached inodes are free when allocated
    Date
    From: Dave Chinner <dchinner@redhat.com>

    commit afca6c5b2595fc44383919fba740c194b0b76aff upstream.

    A recent fuzzed filesystem image cached random dcache corruption
    when the reproducer was run. This often showed up as panics in
    lookup_slow() on a null inode->i_ops pointer when doing pathwalks.

    BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
    ....
    Call Trace:
    lookup_slow+0x44/0x60
    walk_component+0x3dd/0x9f0
    link_path_walk+0x4a7/0x830
    path_lookupat+0xc1/0x470
    filename_lookup+0x129/0x270
    user_path_at_empty+0x36/0x40
    path_listxattr+0x98/0x110
    SyS_listxattr+0x13/0x20
    do_syscall_64+0xf5/0x280
    entry_SYSCALL_64_after_hwframe+0x42/0xb7

    but had many different failure modes including deadlocks trying to
    lock the inode that was just allocated or KASAN reports of
    use-after-free violations.

    The cause of the problem was a corrupt INOBT on a v4 fs where the
    root inode was marked as free in the inobt record. Hence when we
    allocated an inode, it chose the root inode to allocate, found it in
    the cache and re-initialised it.

    We recently fixed a similar inode allocation issue caused by inobt
    record corruption problem in xfs_iget_cache_miss() in commit
    ee457001ed6c ("xfs: catch inode allocation state mismatch
    corruption"). This change adds similar checks to the cache-hit path
    to catch it, and turns the reproducer into a corruption shutdown
    situation.

    Reported-by: Wen Xu <wen.xu@gatech.edu>
    Signed-Off-By: Dave Chinner <dchinner@redhat.com>
    Reviewed-by: Christoph Hellwig <hch@lst.de>
    Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
    Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
    [darrick: fix typos in comment]
    Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
    Signed-off-by: Siddharth Chandrasekaran <csiddharth@vmware.com>
    ---
    fs/xfs/xfs_icache.c | 57 ++++++++++++++++++++++++++++++++++++++++++++++-------
    1 file changed, 50 insertions(+), 7 deletions(-)

    diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
    index adbc1f5..7efeefb 100644
    --- a/fs/xfs/xfs_icache.c
    +++ b/fs/xfs/xfs_icache.c
    @@ -135,6 +135,46 @@ xfs_inode_free(
    }

    /*
    + * If we are allocating a new inode, then check what was returned is
    + * actually a free, empty inode. If we are not allocating an inode,
    + * then check we didn't find a free inode.
    + *
    + * Returns:
    + * 0 if the inode free state matches the lookup context
    + * -ENOENT if the inode is free and we are not allocating
    + * -EFSCORRUPTED if there is any state mismatch at all
    + */
    +static int
    +xfs_iget_check_free_state(
    + struct xfs_inode *ip,
    + int flags)
    +{
    + if (flags & XFS_IGET_CREATE) {
    + /* should be a free inode */
    + if (VFS_I(ip)->i_mode != 0) {
    + xfs_warn(ip->i_mount,
    +"Corruption detected! Free inode 0x%llx not marked free! (mode 0x%x)",
    + ip->i_ino, VFS_I(ip)->i_mode);
    + return -EFSCORRUPTED;
    + }
    +
    + if (ip->i_d.di_nblocks != 0) {
    + xfs_warn(ip->i_mount,
    +"Corruption detected! Free inode 0x%llx has blocks allocated!",
    + ip->i_ino);
    + return -EFSCORRUPTED;
    + }
    + return 0;
    + }
    +
    + /* should be an allocated inode */
    + if (VFS_I(ip)->i_mode == 0)
    + return -ENOENT;
    +
    + return 0;
    +}
    +
    +/*
    * Check the validity of the inode we just found it the cache
    */
    static int
    @@ -183,12 +223,12 @@ xfs_iget_cache_hit(
    }

    /*
    - * If lookup is racing with unlink return an error immediately.
    + * Check the inode free state is valid. This also detects lookup
    + * racing with unlinks.
    */
    - if (ip->i_d.di_mode == 0 && !(flags & XFS_IGET_CREATE)) {
    - error = -ENOENT;
    + error = xfs_iget_check_free_state(ip, flags);
    + if (error)
    goto out_error;
    - }

    /*
    * If IRECLAIMABLE is set, we've torn down the VFS inode already.
    @@ -298,10 +338,13 @@ xfs_iget_cache_miss(

    trace_xfs_iget_miss(ip);

    - if ((ip->i_d.di_mode == 0) && !(flags & XFS_IGET_CREATE)) {
    - error = -ENOENT;
    + /*
    + * Check the inode free state is valid. This also detects lookup
    + * racing with unlinks.
    + */
    + error = xfs_iget_check_free_state(ip, flags);
    + if (error)
    goto out_destroy;
    - }

    /*
    * Preload the radix tree so we can insert safely under the
    --
    2.7.4
    \
     
     \ /
      Last update: 2020-05-14 23:03    [W:3.228 / U:1.300 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site