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SubjectRe: [PATCH 1/3] modpost: add array range check to sec_name()
On Wed, Aug 3, 2022 at 2:55 AM Nick Desaulniers <ndesaulniers@google.com> wrote:
>
> On Sat, Jul 30, 2022 at 10:37 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
> >
> > The section index is always positive, so the argunent, secindex, should
> > be unsigned.
> >
> > Also, inserted the array range check.
> >
> > If sym->st_shndx is a special section index (between SHN_LORESERVE and
> > SHN_HIRESERVE), there is no corresponding section header.
> >
> > For example, if a symbol specifies an absolute value, sym->st_shndx is
> > SHN_ABS (=0xfff1).
> >
> > The current users do not cause the out-of-range access of
> > info->sechddrs[], but it is better to avoid such a pitfall.
> >
> > Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
>
> I don't mind adding this check; though if it's anomalous I think we
> could also just print to stderr and abort.


If sec_name() has a failure path,
I need to add another check before calling sec_name().


I want to get a return value that can be safely passed
to strcmp(), etc.


For example,

strcmp(!sec_name(elf, secindex), "some_pattern");


Returning "" for special sections
will work nicely without additional check code.



I am changing the code with a bigger picture in my mind,
although that may not be so clear if you look at this patch only.



> I would prefer Elf_Sym over unsigned int though. WDYT?
>

In /usr/include/elf.h, Elf{32,64}_Sym are structures.
How to use it instead of unsigned int?


typedef struct
{
Elf32_Word st_name; /* Symbol name (string tbl index) */
Elf32_Addr st_value; /* Symbol value */
Elf32_Word st_size; /* Symbol size */
unsigned char st_info; /* Symbol type and binding */
unsigned char st_other; /* Symbol visibility */
Elf32_Section st_shndx; /* Section index */
} Elf32_Sym;

typedef struct
{
Elf64_Word st_name; /* Symbol name (string tbl index) */
unsigned char st_info; /* Symbol type and binding */
unsigned char st_other; /* Symbol visibility */
Elf64_Section st_shndx; /* Section index */
Elf64_Addr st_value; /* Symbol value */
Elf64_Xword st_size; /* Symbol size */
} Elf64_Sym;




Best Regards
Masahiro Yamada

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