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authorGustavo A. R. Silva <gustavo@embeddedor.com>2020-01-21 11:21:38 -0600
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2020-01-23 19:22:49 +0100
commit85f4c95172d606dd66f7ee1fa50c45a245535ffd (patch)
tree5f4a8806668484c6a48c508c33036a499091a5e9 /arch/arm64/lib/memmove.S
parenttty: baudrate: SPARC supports few more baud rates (diff)
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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 76497732932f ("cxgb3/l2t: Fix undefined behaviour") [4] https://lore.kernel.org/lkml/60e14fb7-8596-e21c-f4be-546ce39e7bdb@embeddedor.com/ [5] commit 553d66cb1e86 ("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>
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