tty: n_hdlc: Use flexible-array member and struct_size() helper
Old code in the kernel uses 1-byte and 0-byte arrays to indicate the presence of a "variable length array": struct something { int length; u8 data[1]; }; struct something *instance; instance = kmalloc(sizeof(*instance) + size, GFP_KERNEL); instance->length = size; memcpy(instance->data, source, size); There is also 0-byte arrays. Both cases pose confusion for things like sizeof(), CONFIG_FORTIFY_SOURCE, etc.[1] Instead, the preferred mechanism to declare variable-length types such as the one above is a flexible array member[2] which need to be the last member of a structure and empty-sized: struct something { int stuff; u8 data[]; }; Also, 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 inadvertenly introduced[3] to the codebase from now on. Lastly, make use of the struct_size() helper to safely calculate the allocation size for instances of struct n_hdlc_buf and avoid any potential type mistakes[4][5]. [1] https://github.com/KSPP/linux/issues/21 [2] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [3] commit 76497732 ("cxgb3/l2t: Fix undefined behaviour") [4] https://lore.kernel.org/lkml/60e14fb7-8596-e21c-f4be-546ce39e7bdb@embeddedor.com/ [5] commit 553d66cb ("iommu/vt-d: Use struct_size() helper") Signed-off-by:Gustavo A. R. Silva <gustavo@embeddedor.com> Reviewed-by:
Jiri Slaby <jslaby@suse.cz> Link: https://lore.kernel.org/r/20200121172138.GA3162@embeddedor Signed-off-by:
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Loading
Please register or sign in to comment