[Bug libc/31383] New: _FORTIFY_SOURCE==3 and __fortified_attr_access vs size of 0 and zero size types

["pinskia at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=31383

            Bug ID: 31383
           Summary: _FORTIFY_SOURCE==3 and __fortified_attr_access vs size
                    of 0 and zero size types
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: pinskia at gcc dot gnu.org
                CC: drepper.fsp at gmail dot com
  Target Milestone: ---

__fortified_attr_access seems to be defined incorrectly for _FORTIFY_SOURCE==3.
The documentation for the size-index of access attribute
(https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-access-function-attribute)
has the following:
```
When no size-index argument is specified, the pointer argument must be either
null or point to a space that is suitably aligned and large for __at least one
object__ of the referenced type (this implies that a past-the-end pointer is
not a valid argument).
```

Notice the __at least__ part here. That means the definition of
__fortified_attr_access is wrong when _FORTIFY_SOURCE==3, when passing around 0
size structs.

An example is:
```

#include <stdio.h>
#include <unistd.h>

int main(void) {
    struct test_st {};
    int fd = 0;
    int count = 0;

    struct test_st test_info[16];

    count = read(fd, test_info, sizeof(test_info));
    return(0);
}
```

With _FORTIFY_SOURCE==3 we get:
 __attribute__ ((__access__ (__write_only__, 2)))

Which means the size has to be at least 1 but test_info has size of 0 and we
are passing a size of 0 to read even.

This is moved from GCC bug: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113922
.

-- 
You are receiving this mail because:
You are on the CC list for the bug.