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Message-ID: <20200219034447.GB1663@brightrain.aerifal.cx> Date: Tue, 18 Feb 2020 22:47:37 -0500 From: Rich Felker <dalias@...c.org> To: musl@...ts.openwall.com Subject: Re: [PATCH] stdio: Fix fdopen bug On Wed, Feb 19, 2020 at 10:37:29AM +0800, Zhang Tianci wrote: > Currently, in musl the fdopen doesn't check the consistence between > fd's mode and corresponding file's mode. > > For example, > > int fd = open("file1", O_RDONLY); > FILE *f = fdopen(fd, "W") > > In musl, above code will be Okay. > While according to POSIX, above code (fdopen) will return EINVAL. > > Signed-off-by: Zhang Tianci <zhangtianci1@...wei.com> > --- > src/stdio/__fdopen.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/src/stdio/__fdopen.c b/src/stdio/__fdopen.c > index 116e78e..23c4ffd 100644 > --- a/src/stdio/__fdopen.c > +++ b/src/stdio/__fdopen.c > @@ -26,6 +26,16 @@ FILE *__fdopen(int fd, const char *mode) > /* Impose mode restrictions */ > if (!strchr(mode, '+')) f->flags = (*mode == 'r') ? F_NOWR : F_NORD; > > + int fd_flag = __syscall(SYS_fcntl, fd, F_GETFL); > + > + if (fd_flag == -1) return 0; > + > + if (((fd_flag & O_ACCMODE) == O_RDONLY && !(f->flags & F_NORD)) || > + ((fd_flag & O_ACCMODE) == O_WRONLY && !(f->flags & F_NOWR))) { > + errno = EINVAL; > + return 0; > + } > + > /* Apply close-on-exec flag */ > if (strchr(mode, 'e')) __syscall(SYS_fcntl, fd, F_SETFD, FD_CLOEXEC); > > -- > 2.17.1 Per POSIX this is a "may fail" not a "shall fail". Testing for this is more costly (see added code/syscalls in the patch) and serves no purpose, which is why it's not done. Rich
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