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[Xen-devel] [PATCH 2/3] libxl: Hold the atfork lock while closing carefd

This avoids the process being forked while a carefd is recorded in the
list but the actual fd has been closed.  If that happened, a
subsequent libxl_postfork_child_noexec would attempt to close the fd
again.  If we are lucky that results in a harmless warning; but if we
are unlucky the fd number has been reused and we close an unrelated

This race has not been observed anywhere as far as we are aware.

Signed-off-by: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
CC: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
CC: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
 tools/libxl/libxl_fork.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/libxl/libxl_fork.c b/tools/libxl/libxl_fork.c
index 8421296..fa15095 100644
--- a/tools/libxl/libxl_fork.c
+++ b/tools/libxl/libxl_fork.c
@@ -184,9 +184,9 @@ void libxl_postfork_child_noexec(libxl_ctx *ctx)
 int libxl__carefd_close(libxl__carefd *cf)
     if (!cf) return 0;
+    atfork_lock();
     int r = cf->fd < 0 ? 0 : close(cf->fd);
     int esave = errno;
-    atfork_lock();
     LIBXL_LIST_REMOVE(cf, entry);

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