lkml.org 
[lkml]   [2020]   [May]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH] fanotify: Replace zero-length array with flexible-array
    On Thu 07-05-20 13:52:30, Gustavo A. R. Silva wrote:
    > The current codebase makes use of the zero-length array language
    > extension to the C90 standard, but the preferred mechanism to declare
    > variable-length types such as these ones is a flexible array member[1][2],
    > introduced in C99:
    >
    > struct foo {
    > int stuff;
    > struct boo array[];
    > };
    >
    > By making use of the mechanism above, we will get a compiler warning
    > in case the flexible array does not occur last in the structure, which
    > will help us prevent some kind of undefined behavior bugs from being
    > inadvertently introduced[3] to the codebase from now on.
    >
    > Also, notice that, dynamic memory allocations won't be affected by
    > this change:
    >
    > "Flexible array members have incomplete type, and so the sizeof operator
    > may not be applied. As a quirk of the original implementation of
    > zero-length arrays, sizeof evaluates to zero."[1]
    >
    > sizeof(flexible-array-member) triggers a warning because flexible array
    > members have incomplete type[1]. There are some instances of code in
    > which the sizeof operator is being incorrectly/erroneously applied to
    > zero-length arrays and the result is zero. Such instances may be hiding
    > some bugs. So, this work (flexible-array member conversions) will also
    > help to get completely rid of those sorts of issues.
    >
    > This issue was found with the help of Coccinelle.
    >
    > [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
    > [2] https://github.com/KSPP/linux/issues/21
    > [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
    >
    > Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

    Thanks. I've added the patch to my tree.

    Honza

    > ---
    > fs/notify/fanotify/fanotify.h | 2 +-
    > 1 file changed, 1 insertion(+), 1 deletion(-)
    >
    > diff --git a/fs/notify/fanotify/fanotify.h b/fs/notify/fanotify/fanotify.h
    > index 35bfbf4a7aac..8ce7ccfc4b0d 100644
    > --- a/fs/notify/fanotify/fanotify.h
    > +++ b/fs/notify/fanotify/fanotify.h
    > @@ -89,7 +89,7 @@ struct fanotify_name_event {
    > __kernel_fsid_t fsid;
    > struct fanotify_fh dir_fh;
    > u8 name_len;
    > - char name[0];
    > + char name[];
    > };
    >
    > static inline struct fanotify_name_event *
    >
    --
    Jan Kara <jack@suse.com>
    SUSE Labs, CR

    \
     
     \ /
      Last update: 2020-05-08 10:39    [W:4.551 / U:0.016 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site