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Message-ID: <5oy5qyky5nwrgptkagm3nageam4btklbhgd3dupxzmcmlerd4w@bagvved6hrym>
Date: Mon, 17 Feb 2025 14:43:36 +0100
From: Alejandro Colomar <alx@...nel.org>
To: Karlson2k <k2k@...od.ru>
Cc: libc-help@...rceware.org, linux-man@...r.kernel.org,
Tobias Stoeckmann <tobias@...eckmann.org>, Serge Hallyn <serge@...lyn.com>,
Iker Pedrosa <ipedrosa@...hat.com>, shadow-utils <~hallyn/shadow@...ts.sr.ht>,
Rich Felker <dalias@...c.org>, musl@...ts.openwall.com
Subject: Re: [shadow-maint/shadow] Add cheap defense mechanisms (PR #1171)
Hi,
On Mon, Feb 17, 2025 at 10:42:11AM +0100, Alejandro Colomar wrote:
> On Sun, Feb 16, 2025 at 06:15:18PM -0800, Karlson2k wrote:
> > Karlson2k left a comment (shadow-maint/shadow#1171)
> >
> > Doesn't use of glibc extensions break functioning with non-glibc, like musl?
After reading musl's source code, it does support 'e'. And it does so
since 2012. Which libc are you using? And which version?
alx@...uan:~/src/musl/libc/master$ grepc fopen .
./include/stdio.h:FILE *fopen(const char *__restrict, const char *__restrict);
./src/stdio/fopen.c:FILE *fopen(const char *restrict filename, const char *restrict mode)
{
FILE *f;
int fd;
int flags;
/* Check for valid initial mode character */
if (!strchr("rwa", *mode)) {
errno = EINVAL;
return 0;
}
/* Compute the flags to pass to open() */
flags = __fmodeflags(mode);
fd = sys_open(filename, flags, 0666);
if (fd < 0) return 0;
if (flags & O_CLOEXEC)
__syscall(SYS_fcntl, fd, F_SETFD, FD_CLOEXEC);
f = __fdopen(fd, mode);
if (f) return f;
__syscall(SYS_close, fd);
return 0;
}
alx@...uan:~/src/musl/libc/master$ grepc __fmodeflags .
./src/stdio/__fmodeflags.c:int __fmodeflags(const char *mode)
{
int flags;
if (strchr(mode, '+')) flags = O_RDWR;
else if (*mode == 'r') flags = O_RDONLY;
else flags = O_WRONLY;
if (strchr(mode, 'x')) flags |= O_EXCL;
if (strchr(mode, 'e')) flags |= O_CLOEXEC;
if (*mode != 'r') flags |= O_CREAT;
if (*mode == 'w') flags |= O_TRUNC;
if (*mode == 'a') flags |= O_APPEND;
return flags;
}
./src/internal/stdio_impl.h:hidden int __fmodeflags(const char *);
alx@...uan:~/src/musl/libc/master$ git blame -- src/stdio/__fmodeflags.c | grep CLOEXEC
892cafff6 (Rich Felker 2012-10-24 21:16:06 -0400 11) if (strchr(mode, 'e')) flags |= O_CLOEXEC;
alx@...uan:~/src/musl/libc/master$ git show 892cafff6 | grep -e CLOEXEC -e ^diff | head -n5
diff --git a/src/internal/stdio_impl.h b/src/internal/stdio_impl.h
diff --git a/src/stdio/__fmodeflags.c b/src/stdio/__fmodeflags.c
+ if (strchr(mode, 'e')) flags |= O_CLOEXEC;
diff --git a/src/stdio/fopen.c b/src/stdio/fopen.c
- if (strchr(mode, 'e')) flags |= O_CLOEXEC;
alx@...uan:~/src/musl/libc/master$ git blame 892cafff6^ -- src/stdio/fopen.c | grep CLOEXEC
8582a6e9f (Rich Felker 2012-09-29 18:09:34 -0400 20) if (strchr(mode, 'e')) flags |= O_CLOEXEC;
alx@...uan:~/src/musl/libc/master$ git log -1 8582a6e9f
commit 8582a6e9f25dd7b87d72961f58008052a4cac473
Author: Rich Felker <dalias@...ifal.cx>
Date: Sat Sep 29 18:09:34 2012 -0400
add 'e' modifier (close-on-exec) to fopen and fdopen
this feature will be in the next version of POSIX, and can be used
internally immediately. there are many internal uses of fopen where
close-on-exec is needed to fix bugs.
Cheers,
Alex
--
<https://www.alejandro-colomar.es/>
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