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* [Bug libc/31383] New: _FORTIFY_SOURCE==3 and __fortified_attr_access vs size of 0 and zero size types
@ 2024-02-14 21:06 pinskia at gcc dot gnu.org
  2024-02-14 21:13 ` [Bug libc/31383] " sam at gentoo dot org
                   ` (10 more replies)
  0 siblings, 11 replies; 12+ messages in thread
From: pinskia at gcc dot gnu.org @ 2024-02-14 21:06 UTC (permalink / raw)
  To: glibc-bugs

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
.

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^ permalink raw reply	[flat|nested] 12+ messages in thread
end of thread, other threads:[~2024-02-28 13:36 UTC | newest]

Thread overview: 12+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2024-02-14 21:06 [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
2024-02-14 21:13 ` [Bug libc/31383] " sam at gentoo dot org
2024-02-14 21:15 ` sergiodj at sergiodj dot net
2024-02-14 21:20 ` sam at gentoo dot org
2024-02-14 21:20 ` [Bug libc/31383] _FORTIFY_SOURCE=3 " sam at gentoo dot org
2024-02-14 23:40 ` andreas at canonical dot com
2024-02-15 13:17 ` siddhesh at sourceware dot org
2024-02-15 17:16 ` siddhesh at sourceware dot org
2024-02-15 20:16 ` siddhesh at sourceware dot org
2024-02-28 13:35 ` cvs-commit at gcc dot gnu.org
2024-02-28 13:36 ` siddhesh at sourceware dot org
2024-02-28 13:36 ` siddhesh at sourceware dot org

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