From: Paul Moore <paul@paul-moore.com> To: "Gustavo A. R. Silva" <gustavoars@kernel.org> Cc: Eric Paris <eparis@redhat.com>, linux-audit@redhat.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH] audit: Replace zero-length array with flexible-array Date: Thu, 7 May 2020 22:52:09 -0400 [thread overview] Message-ID: <CAHC9VhSm_GWWXuzuwrrcTF3QcKCv1WSZv2=WF4t3DB4P7vshoA@mail.gmail.com> (raw) In-Reply-To: <20200507185041.GA13930@embeddedor> On Thu, May 7, 2020 at 2:46 PM Gustavo A. R. Silva <gustavoars@kernel.org> 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@kernel.org> > --- > include/linux/audit.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) Merged into audit/next, thanks! > 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; -- paul moore www.paul-moore.com
WARNING: multiple messages have this Message-ID (diff)
From: Paul Moore <paul@paul-moore.com> To: "Gustavo A. R. Silva" <gustavoars@kernel.org> Cc: linux-audit@redhat.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH] audit: Replace zero-length array with flexible-array Date: Thu, 7 May 2020 22:52:09 -0400 [thread overview] Message-ID: <CAHC9VhSm_GWWXuzuwrrcTF3QcKCv1WSZv2=WF4t3DB4P7vshoA@mail.gmail.com> (raw) In-Reply-To: <20200507185041.GA13930@embeddedor> On Thu, May 7, 2020 at 2:46 PM Gustavo A. R. Silva <gustavoars@kernel.org> 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@kernel.org> > --- > include/linux/audit.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) Merged into audit/next, thanks! > 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; -- paul moore www.paul-moore.com -- Linux-audit mailing list Linux-audit@redhat.com https://www.redhat.com/mailman/listinfo/linux-audit
next prev parent reply other threads:[~2020-05-08 2:52 UTC|newest] Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-05-07 18:50 [PATCH] audit: Replace zero-length array with flexible-array Gustavo A. R. Silva 2020-05-07 18:50 ` Gustavo A. R. Silva 2020-05-07 21:58 ` Richard Guy Briggs 2020-05-07 21:58 ` Richard Guy Briggs 2020-05-07 22:49 ` Gustavo A. R. Silva 2020-05-07 22:49 ` Gustavo A. R. Silva 2020-05-08 2:48 ` Paul Moore 2020-05-08 2:48 ` Paul Moore 2020-05-08 11:17 ` Richard Guy Briggs 2020-05-08 11:17 ` Richard Guy Briggs 2020-05-08 2:52 ` Paul Moore [this message] 2020-05-08 2:52 ` Paul Moore 2020-05-08 23:51 ` Gustavo A. R. Silva 2020-05-08 23:51 ` Gustavo A. R. Silva
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