Re: [PATCH] Fix FORTIFY_SOURCE false positive

["Volker Weißmann" <volker.weissmann@gmx.de>]

On 02.10.23 20:00, Siddhesh Poyarekar wrote:
>
> Also, if you don't have a copyright assignment on file with the FSF,
> could you add a Signed-off-by to certify your contribution?

This is my first patch I sent to a mailing list, so forgive me if the
formatting is wrong:


When -D_FORTIFY_SOURCE=2 was given during compilation,

sprintf and similar functions will check if their
first argument is in read-only memory and exit with
*** %n in writable segment detected ***
otherwise. To check if the memory is read-only, glibc
reads form the file "/proc/self/maps". If opening this
file fails due to too many open files (EMFILE), glibc
will now ignore this error.

Signed-off-by: Volker Weißmann <volker.weissmann@gmx.de>
---
  sysdeps/unix/sysv/linux/readonly-area.c | 10 +++++++++-
  1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/sysdeps/unix/sysv/linux/readonly-area.c
b/sysdeps/unix/sysv/linux/readonly-area.c
index edc68873f6..629163461a 100644
--- a/sysdeps/unix/sysv/linux/readonly-area.c
+++ b/sysdeps/unix/sysv/linux/readonly-area.c
@@ -42,7 +42,15 @@ __readonly_area (const char *ptr, size_t size)
           to the /proc filesystem if it is set[ug]id.  There has
           been no willingness to change this in the kernel so
           far.  */
-      || errno == EACCES)
+      || errno == EACCES
+          /* Example code to trigger EMFILE:
+          while(1) {
+            FILE *file = fopen("/dev/zero", "r");
+            assert(file != NULL);
+          }
+          If your libc was compiled with -D_FORTIFY_SOURCE=2, we run
+          into this if clause here. */
+          || errno == EMFILE)
      return 1;
        return -1;
      }
--
2.42.0
>
> Thanks,
> Sid