[PATCH v2 11/11] bisect: handle dup() failure when redirecting stdout

From: Johannes Schindelin <[email protected]>

To capture the output of each verdict command, bisect_run()
temporarily redirects stdout to a temporary file via the classic
dup(1) / dup2() pair, restoring it afterwards. The return value of
dup(1) is not checked, however. When it fails, the saved descriptor
is -1, which is then passed to close() (the issue Coverity flags),
and the matching dup2() that is meant to restore stdout also fails,
leaving the process with stdout still pointing at the temporary file
for the remainder of the run.

Treat a failed dup(1) or dup2(..., 1) as a fatal error for this bisect
step: close the temporary file descriptor, report the error via
error_errno(), and break out of the loop so the existing cleanup path
handles the rest, just as on other failure paths in this function.

Reported by Coverity as CID 1508242 ("Improper use of negative
value").

Assisted-by: Opus 4.7
Helped-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Johannes Schindelin <[email protected]>
---
 builtin/bisect.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/builtin/bisect.c b/builtin/bisect.c
index ceb60b0626..733d28d377 100644
--- a/builtin/bisect.c
+++ b/builtin/bisect.c
@@ -1308,7 +1308,12 @@ static int bisect_run(struct bisect_terms *terms, int argc, const char **argv)
 
 		fflush(stdout);
 		saved_stdout = dup(1);
-		dup2(temporary_stdout_fd, 1);
+		if (saved_stdout < 0 ||
+		    dup2(temporary_stdout_fd, 1) < 0) {
+			res = error_errno(_("could not duplicate stdout"));
+			close(temporary_stdout_fd);
+			break;
+		}
 
 		res = bisect_state(terms, 1, &new_state);
 
-- 
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