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bpo-32849: Fix is_valid_fd() on FreeBSD #12852

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Merged
vstinner merged 1 commit into from
Apr 17, 2019
Merged

bpo-32849: Fix is_valid_fd() on FreeBSD #12852

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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2019-04-16-11-56-12.bpo-32849.aeSg-D.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Fix Python Initialization code on FreeBSD to detect properly when stdin file
descriptor (fd 0) is invalid.
38 changes: 23 additions & 15 deletions Python/pylifecycle.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1664,26 +1664,34 @@ initsite(void)
static int
is_valid_fd(int fd)
{
#ifdef __APPLE__
/* bpo-30225: On macOS Tiger, when stdout is redirected to a pipe
and the other side of the pipe is closed, dup(1) succeed, whereas
fstat(1, &st) fails with EBADF. Prefer fstat() over dup() to detect
such error. */
struct stat st;
return (fstat(fd, &st) == 0);
#else
int fd2;
if (fd < 0)
/* dup() is faster than fstat(): fstat() can require input/output operations,
whereas dup() doesn't. There is a low risk of EMFILE/ENFILE at Python
startup. Problem: dup() doesn't check if the file descriptor is valid on
some platforms.

bpo-30225: On macOS Tiger, when stdout is redirected to a pipe and the other
side of the pipe is closed, dup(1) succeed, whereas fstat(1, &st) fails with
EBADF. FreeBSD has similar issue (bpo-32849).

Only use dup() on platforms where dup() is enough to detect invalid FD in
corner cases: on Linux and Windows (bpo-32849). */
#if defined(__linux__) || defined(MS_WINDOWS)
if (fd < 0) {
return 0;
}
int fd2;

_Py_BEGIN_SUPPRESS_IPH
/* Prefer dup() over fstat(). fstat() can require input/output whereas
dup() doesn't, there is a low risk of EMFILE/ENFILE at Python
startup. */
fd2 = dup(fd);
if (fd2 >= 0)
if (fd2 >= 0) {
close(fd2);
}
_Py_END_SUPPRESS_IPH
return fd2 >= 0;

return (fd2 >= 0);
#else
struct stat st;
return (fstat(fd, &st) == 0);
#endif
}

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