On 2020-05-07 13:50, 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(a)kernel.org&gt; Sounds reasonable to me. There's another in include/uapi/linux/audit.h

in struct audit_rule_data buf[0]. This alert also helped me fix another one in a patchset I'm about to post (and will probably cause a merge conflict but we can figure that out).

Reviewed-by: Richard Guy Briggs <rgb(a)redhat.com&gt;

> --- > include/linux/audit.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/linux/audit.h b/include/linux/audit.h > index f9ceae57ca8d..2b63aee6e9fa 100644 > --- a/include/linux/audit.h > +++ b/include/linux/audit.h > @@ -19,7 +19,7 @@ > struct audit_sig_info { > uid_t uid; > pid_t pid; > - char ctx[0]; > + char ctx[]; > }; > > struct audit_buffer; > > > -- > Linux-audit mailing list > Linux-audit(a)redhat.com > https://www.redhat.com/mailman/listinfo/linux-audit - RGB -- Richard Guy Briggs <rgb(a)redhat.com&gt; Sr. S/W Engineer, Kernel Security, Base Operating Systems Remote, Ottawa, Red Hat Canada IRC: rgb, SunRaycer Voice: +1.647.777.2635, Internal: (81) 32635

On Thu, May 07, 2020 at 05:58:13PM -0400, Richard Guy Briggs wrote: > On 2020-05-07 13:50, 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(a)kernel.org&gt; > > Sounds reasonable to me. There's another in include/uapi/linux/audit.h Hi,

I wouldn't advise to make any of these conversions in include/uapi/ [1][2].

> in struct audit_rule_data buf[0]. This alert also helped me fix another > one in a patchset I'm about to post (and will probably cause a merge > conflict but we can figure that out). Awesome. :) > Reviewed-by: Richard Guy Briggs <rgb(a)redhat.com&gt; Thanks -- Gustavo [1] https://lore.kernel.org/lkml/20200424121553.GE26002@ziepe.ca/ [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit... > > --- > > include/linux/audit.h | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/include/linux/audit.h b/include/linux/audit.h > > index f9ceae57ca8d..2b63aee6e9fa 100644 > > --- a/include/linux/audit.h > > +++ b/include/linux/audit.h > > @@ -19,7 +19,7 @@ > > struct audit_sig_info { > > uid_t uid; > > pid_t pid; > > - char ctx[0]; > > + char ctx[]; > > }; > > > > struct audit_buffer; > > - RGB