bpo-32844: Fix a subprocess misredirection of a low fd (GH5689)
bpo-32844: subprocess: Fix a potential misredirection of a low fd to stderr.
When redirecting, subprocess attempts to achieve the following state:
each fd to be redirected to is less than or equal to the fd
it is redirected from, which is necessary because redirection
occurs in the ascending order of destination descriptors.
It fails to do so in a couple of corner cases,
for example, if 1 is redirected to 2 and 0 is closed in the parent.
diff --git a/Modules/_posixsubprocess.c b/Modules/_posixsubprocess.c
index dc43ffc..0150fcb 100644
--- a/Modules/_posixsubprocess.c
+++ b/Modules/_posixsubprocess.c
@@ -424,7 +424,7 @@
either 0, 1 or 2, it is possible that it is overwritten (#12607). */
if (c2pwrite == 0)
POSIX_CALL(c2pwrite = dup(c2pwrite));
- if (errwrite == 0 || errwrite == 1)
+ while (errwrite == 0 || errwrite == 1)
POSIX_CALL(errwrite = dup(errwrite));
/* Dup fds for child.