From: Paul Eggert <eggert@cs.ucla.edu>
To: Florian Weimer <fweimer@redhat.com>
Cc: libc-alpha@sourceware.org,
Samuel Thibault <samuel.thibault@ens-lyon.org>
Subject: Re: [PATCH 1/3] <fd_to_filename.h>: Add type safety and port to Hurd
Date: Sat, 15 Feb 2020 16:02:28 -0800 [thread overview]
Message-ID: <d85f47f4-8d41-70df-a4a2-2fa3ad4110ec@cs.ucla.edu> (raw)
In-Reply-To: <87wo8oxa63.fsf@oldenburg2.str.redhat.com>
On 2/15/20 5:16 AM, Florian Weimer wrote:
> INT_STRLEN_BOUND is 11, right?
Yes, it's a bound on the string length of a printed int, and that's 11 in the
typical case of 32-bit int because the int might be negative. I didn't lose
sleep over the wasted byte, but if we want a tighter bound then we could use
INT_STRLEN_BOUND (int) - 1 instead. However, it might be better to leave it
alone so that we can use the code below.
> The problem is when an application passes an invalid descriptor to some
> libc function and that ends up with __fd_to_filename. We should not
> make matters worse in that case.
If it's not a precondition that the descriptor is nonnegative, we can't simply
return a copy of FD_TO_FILENAME_PREFIX as that's an existing filename. Instead,
how about the following? It uses a randomish garbage filename beginning with "-"
which should be good enough, and it doesn't cost a conditional branch to handle
negative descriptors.
char *
__fd_to_filename (int descriptor, struct fd_to_filename *storage)
{
char *p = mempcpy (storage->buffer, FD_TO_FILENAME_PREFIX,
strlen (FD_TO_FILENAME_PREFIX) - 1);
/* If DESCRIPTOR is negative, arrange for the filename to not exist
by prepending any byte other than '/', '.', '\0' or an ASCII digit.
The rest of the filename will be gibberish that fits. */
*p = '-';
p += descriptor < 0;
for (int d = descriptor; p++, (d /= 10) != 0; )
continue;
*p = '\0';
for (int d = descriptor; *--p = '0' + d % 10, (d /= 10) != 0; )
continue;
return storage->buffer;
}
next prev parent reply other threads:[~2020-02-16 0:02 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-14 18:10 [PATCH 0/3] <fd_to_filename.h> improvements Florian Weimer
2020-02-14 18:11 ` [PATCH 1/3] <fd_to_filename.h>: Add type safety and port to Hurd Florian Weimer
2020-02-14 18:43 ` Samuel Thibault
2020-02-14 19:08 ` Adhemerval Zanella
2020-02-14 20:21 ` Florian Weimer
2020-02-14 20:28 ` Paul Eggert
2020-02-15 13:16 ` Florian Weimer
2020-02-16 0:02 ` Paul Eggert [this message]
2020-02-17 15:18 ` Florian Weimer
2020-02-17 18:26 ` Paul Eggert
2020-02-17 18:59 ` Adhemerval Zanella
2020-02-17 19:14 ` Paul Eggert
2020-02-14 18:11 ` [PATCH 2/3] Linux: Port ttyname, ttyname_r to <fd_file_name.h> Florian Weimer
2020-02-14 18:11 ` [PATCH 3/3] Linux: Port fexecve to <fd_to_filename.h> Florian Weimer
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