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    Subject[PATCH 4.4 041/241] cifs: fix strcat buffer overflow and reduce raciness in smb21_set_oplock_level()
    Date
    From: Christoph Probst <kernel@probst.it>

    commit 6a54b2e002c9d00b398d35724c79f9fe0d9b38fb upstream.

    Change strcat to strncpy in the "None" case to fix a buffer overflow
    when cinode->oplock is reset to 0 by another thread accessing the same
    cinode. It is never valid to append "None" to any other message.

    Consolidate multiple writes to cinode->oplock to reduce raciness.

    Signed-off-by: Christoph Probst <kernel@probst.it>
    Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
    Signed-off-by: Steve French <stfrench@microsoft.com>
    CC: Stable <stable@vger.kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/cifs/smb2ops.c | 14 ++++++++------
    1 file changed, 8 insertions(+), 6 deletions(-)

    --- a/fs/cifs/smb2ops.c
    +++ b/fs/cifs/smb2ops.c
    @@ -1329,26 +1329,28 @@ smb21_set_oplock_level(struct cifsInodeI
    unsigned int epoch, bool *purge_cache)
    {
    char message[5] = {0};
    + unsigned int new_oplock = 0;

    oplock &= 0xFF;
    if (oplock == SMB2_OPLOCK_LEVEL_NOCHANGE)
    return;

    - cinode->oplock = 0;
    if (oplock & SMB2_LEASE_READ_CACHING_HE) {
    - cinode->oplock |= CIFS_CACHE_READ_FLG;
    + new_oplock |= CIFS_CACHE_READ_FLG;
    strcat(message, "R");
    }
    if (oplock & SMB2_LEASE_HANDLE_CACHING_HE) {
    - cinode->oplock |= CIFS_CACHE_HANDLE_FLG;
    + new_oplock |= CIFS_CACHE_HANDLE_FLG;
    strcat(message, "H");
    }
    if (oplock & SMB2_LEASE_WRITE_CACHING_HE) {
    - cinode->oplock |= CIFS_CACHE_WRITE_FLG;
    + new_oplock |= CIFS_CACHE_WRITE_FLG;
    strcat(message, "W");
    }
    - if (!cinode->oplock)
    - strcat(message, "None");
    + if (!new_oplock)
    + strncpy(message, "None", sizeof(message));
    +
    + cinode->oplock = new_oplock;
    cifs_dbg(FYI, "%s Lease granted on inode %p\n", message,
    &cinode->vfs_inode);
    }

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