autofs: use flexible array in ioctl structure

Commit df8fc4e934c1 ("kbuild: Enable -fstrict-flex-arrays=3") introduced a warning
for the autofs_dev_ioctl structure:

In function 'check_name',
    inlined from 'validate_dev_ioctl' at fs/autofs/dev-ioctl.c:131:9,
    inlined from '_autofs_dev_ioctl' at fs/autofs/dev-ioctl.c:624:8:
fs/autofs/dev-ioctl.c:33:14: error: 'strchr' reading 1 or more bytes from a region of size 0 [-Werror=stringop-overread]
   33 |         if (!strchr(name, '/'))
      |              ^~~~~~~~~~~~~~~~~
In file included from include/linux/auto_dev-ioctl.h:10,
                 from fs/autofs/autofs_i.h:10,
                 from fs/autofs/dev-ioctl.c:14:
include/uapi/linux/auto_dev-ioctl.h: In function '_autofs_dev_ioctl':
include/uapi/linux/auto_dev-ioctl.h:112:14: note: source object 'path' of size 0
  112 |         char path[0];
      |              ^~~~

This is easily fixed by changing the gnu 0-length array into a c99
flexible array. Since this is a uapi structure, we have to be careful
about possible regressions but this one should be fine as they are
equivalent here. While it would break building with ancient gcc versions
that predate c99, it helps building with --std=c99 and -Wpedantic builds
in user space, as well as non-gnu compilers. This means we probably
also want it fixed in stable kernels.

Cc: stable@vger.kernel.org
Cc: Kees Cook <keescook@chromium.org>
Cc: Gustavo A. R. Silva" <gustavoars@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20230523081944.581710-1-arnd@kernel.org

diff --git a/Documentation/filesystems/autofs-mount-control.rst b/Documentation/filesystems/autofs-mount-control.rst
index bf4b511..b5a379d 100644 (file)
--- a/Documentation/filesystems/autofs-mount-control.rst
+++ b/Documentation/filesystems/autofs-mount-control.rst
@@ -196,7 +196,7 @@ information and return operation results::
                    struct args_ismountpoint    ismountpoint;
            };
 
-           char path[0];
+           char path[];
     };
 
 The ioctlfd field is a mount point file descriptor of an autofs mount

diff --git a/Documentation/filesystems/autofs.rst b/Documentation/filesystems/autofs.rst
index 4f49027..3b6e38e 100644 (file)
--- a/Documentation/filesystems/autofs.rst
+++ b/Documentation/filesystems/autofs.rst
@@ -467,7 +467,7 @@ Each ioctl is passed a pointer to an `autofs_dev_ioctl` structure::
                        struct args_ismountpoint        ismountpoint;
                };
 
-                char path[0];
+                char path[];
         };
 
 For the **OPEN_MOUNT** and **IS_MOUNTPOINT** commands, the target

diff --git a/include/uapi/linux/auto_dev-ioctl.h b/include/uapi/linux/auto_dev-ioctl.h
index 62e6253..08be539 100644 (file)
--- a/include/uapi/linux/auto_dev-ioctl.h
+++ b/include/uapi/linux/auto_dev-ioctl.h
@@ -109,7 +109,7 @@ struct autofs_dev_ioctl {
                struct args_ismountpoint        ismountpoint;
        };
 
-       char path[0];
+       char path[];
 };
 
 static inline void init_autofs_dev_ioctl(struct autofs_dev_ioctl *in)