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    Subject[PATCH AUTOSEL 4.20 016/117] fanotify: return only user requested event types in event mask
    Date
    From: Matthew Bobrowski <mbobrowski@mbobrowski.org>

    [ Upstream commit 2d10b23082a7eb8be508b3789f2e7250a88a5ddb ]

    Modify fanotify_should_send_event() so that it now returns a mask for
    an event that contains ONLY flags for the event types that have been
    specifically requested by the user. Flags that may have been included
    within the event mask, but have not been explicitly requested by the
    user will not be present in the returned value.

    As an example, given the situation where a user requests events of type
    FAN_OPEN. Traditionally, the event mask returned within an event that
    occurred on a filesystem object that has been marked for monitoring and is
    opened, will only ever have the FAN_OPEN bit set. With the introduction of
    the new flags like FAN_OPEN_EXEC, and perhaps any other future event
    flags, there is a possibility of the returned event mask containing more
    than a single bit set, despite having only requested the single event type.
    Prior to these modifications performed to fanotify_should_send_event(), a
    user would have received a bundled event mask containing flags FAN_OPEN
    and FAN_OPEN_EXEC in the instance that a file was opened for execution via
    execve(), for example. This means that a user would receive event types
    in the returned event mask that have not been requested. This runs the
    possibility of breaking existing systems and causing other unforeseen
    issues.

    To mitigate this possibility, fanotify_should_send_event() has been
    modified to return the event mask containing ONLY event types explicitly
    requested by the user. This means that we will NOT report events that the
    user did no set a mask for, and we will NOT report events that the user
    has set an ignore mask for.

    The function name fanotify_should_send_event() has also been updated so
    that it's more relevant to what it has been designed to do.

    Signed-off-by: Matthew Bobrowski <mbobrowski@mbobrowski.org>
    Reviewed-by: Amir Goldstein <amir73il@gmail.com>
    Signed-off-by: Jan Kara <jack@suse.cz>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    fs/notify/fanotify/fanotify.c | 28 ++++++++++++++++------------
    1 file changed, 16 insertions(+), 12 deletions(-)

    diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
    index e08a6647267b..f4f8359bc597 100644
    --- a/fs/notify/fanotify/fanotify.c
    +++ b/fs/notify/fanotify/fanotify.c
    @@ -89,7 +89,13 @@ static int fanotify_get_response(struct fsnotify_group *group,
    return ret;
    }

    -static bool fanotify_should_send_event(struct fsnotify_iter_info *iter_info,
    +/*
    + * This function returns a mask for an event that only contains the flags
    + * that have been specifically requested by the user. Flags that may have
    + * been included within the event mask, but have not been explicitly
    + * requested by the user, will not be present in the returned mask.
    + */
    +static u32 fanotify_group_event_mask(struct fsnotify_iter_info *iter_info,
    u32 event_mask, const void *data,
    int data_type)
    {
    @@ -101,14 +107,14 @@ static bool fanotify_should_send_event(struct fsnotify_iter_info *iter_info,
    pr_debug("%s: report_mask=%x mask=%x data=%p data_type=%d\n",
    __func__, iter_info->report_mask, event_mask, data, data_type);

    - /* if we don't have enough info to send an event to userspace say no */
    + /* If we don't have enough info to send an event to userspace say no */
    if (data_type != FSNOTIFY_EVENT_PATH)
    - return false;
    + return 0;

    - /* sorry, fanotify only gives a damn about files and dirs */
    + /* Sorry, fanotify only gives a damn about files and dirs */
    if (!d_is_reg(path->dentry) &&
    !d_can_lookup(path->dentry))
    - return false;
    + return 0;

    fsnotify_foreach_obj_type(type) {
    if (!fsnotify_iter_should_report_type(iter_info, type))
    @@ -129,13 +135,10 @@ static bool fanotify_should_send_event(struct fsnotify_iter_info *iter_info,

    if (d_is_dir(path->dentry) &&
    !(marks_mask & FS_ISDIR & ~marks_ignored_mask))
    - return false;
    -
    - if (event_mask & FANOTIFY_OUTGOING_EVENTS &
    - marks_mask & ~marks_ignored_mask)
    - return true;
    + return 0;

    - return false;
    + return event_mask & FANOTIFY_OUTGOING_EVENTS & marks_mask &
    + ~marks_ignored_mask;
    }

    struct fanotify_event_info *fanotify_alloc_event(struct fsnotify_group *group,
    @@ -210,7 +213,8 @@ static int fanotify_handle_event(struct fsnotify_group *group,

    BUILD_BUG_ON(HWEIGHT32(ALL_FANOTIFY_EVENT_BITS) != 10);

    - if (!fanotify_should_send_event(iter_info, mask, data, data_type))
    + mask = fanotify_group_event_mask(iter_info, mask, data, data_type);
    + if (!mask)
    return 0;

    pr_debug("%s: group=%p inode=%p mask=%x\n", __func__, group, inode,
    --
    2.19.1
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