From patchwork Tue Mar 5 22:18:46 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: "Gustavo A. R. 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R. Silva" To: Jan Kara , Amir Goldstein , Alexander Viro , Christian Brauner Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, "Gustavo A. R. Silva" , linux-hardening@vger.kernel.org, Kees Cook Subject: [PATCH][next] fsnotify: Avoid -Wflex-array-member-not-at-end warning Message-ID: Precedence: bulk X-Mailing-List: linux-hardening@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Disposition: inline -Wflex-array-member-not-at-end is coming in GCC-14, and we are getting ready to enable it globally. There is currently a local structure `f` that is using a flexible `struct file_handle` as header for an on-stack place-holder for the flexible-array member `unsigned char f_handle[];`. struct { struct file_handle handle; u8 pad[MAX_HANDLE_SZ]; } f; However, we are deprecating flexible arrays in the middle of another struct. So, in order to avoid this, we use the `struct_group_tagged()` helper to separate the flexible array from the rest of the members in the flexible structure: struct file_handle { struct_group_tagged(file_handle_hdr, hdr, ... the rest of the members ); unsigned char f_handle[]; }; With the change described above, we can now declare an object of the type of the tagged struct, without embedding the flexible array in the middle of another struct: struct { struct file_handle_hdr handle; u8 pad[MAX_HANDLE_SZ]; } f; We also use `container_of()` whenever we need to retrieve a pointer to the flexible structure, through which the flexible-array member can be accessed, as in this case. So, with these changes, fix the following warning: fs/notify/fdinfo.c: In function ‘show_mark_fhandle’: fs/notify/fdinfo.c:45:36: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end] 45 | struct file_handle handle; | ^~~~~~ Signed-off-by: Gustavo A. R. Silva --- fs/notify/fdinfo.c | 8 +++++--- include/linux/fs.h | 6 ++++-- 2 files changed, 9 insertions(+), 5 deletions(-) diff --git a/fs/notify/fdinfo.c b/fs/notify/fdinfo.c index 5c430736ec12..740f5e68b397 100644 --- a/fs/notify/fdinfo.c +++ b/fs/notify/fdinfo.c @@ -42,15 +42,17 @@ static void show_fdinfo(struct seq_file *m, struct file *f, static void show_mark_fhandle(struct seq_file *m, struct inode *inode) { struct { - struct file_handle handle; + struct file_handle_hdr handle; u8 pad[MAX_HANDLE_SZ]; } f; + struct file_handle *handle = container_of(&f.handle, + struct file_handle, hdr); int size, ret, i; f.handle.handle_bytes = sizeof(f.pad); size = f.handle.handle_bytes >> 2; - ret = exportfs_encode_fid(inode, (struct fid *)f.handle.f_handle, &size); + ret = exportfs_encode_fid(inode, (struct fid *)handle->f_handle, &size); if ((ret == FILEID_INVALID) || (ret < 0)) { WARN_ONCE(1, "Can't encode file handler for inotify: %d\n", ret); return; @@ -63,7 +65,7 @@ static void show_mark_fhandle(struct seq_file *m, struct inode *inode) f.handle.handle_bytes, f.handle.handle_type); for (i = 0; i < f.handle.handle_bytes; i++) - seq_printf(m, "%02x", (int)f.handle.f_handle[i]); + seq_printf(m, "%02x", (int)handle->f_handle[i]); } #else static void show_mark_fhandle(struct seq_file *m, struct inode *inode) diff --git a/include/linux/fs.h b/include/linux/fs.h index 00fc429b0af0..7c131bcd948f 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1030,8 +1030,10 @@ struct file { __attribute__((aligned(4))); /* lest something weird decides that 2 is OK */ struct file_handle { - __u32 handle_bytes; - int handle_type; + struct_group_tagged(file_handle_hdr, hdr, + __u32 handle_bytes; + int handle_type; + ); /* file identifier */ unsigned char f_handle[]; };