[PATCH] Bad file descriptor on filtering empty files

From: William Throwe <wtt6@cornell.edu>
Date: Dec 19, 2014, 22:41 UTC
Message-ID: <87sigbmfd5.fsf@cornell.edu>

In git 2.2.0 (also tested on 2.2.0.65.g9abc44b), if an external smudge/clean filter is called on an empty file git reports something like: error: copy-fd: read returned Bad file descriptor error: cannot feed the input to external filter cat error: external filter cat failed

Test case:

mkdir bug cd bug git init git config filter.cat.clean cat git config filter.cat.smudge cat echo '* filter=cat' >.gitattributes touch a git add a

This started in 9035d75a2be9d80d82676504d69553245017f6d4, which introduced the possible call to copy_fd in code called from apply_filter. It appears that NULL as the src argument to apply_filter is being used both as a sentinel value to indicate that the fd should be used instead and also as a representation of the contents of an empty file. I suggest switching to using fd == -1 as the sentinel as shown in the patch below.

Thanks, Will

diff --git a/convert.c b/convert.c
index 9a5612e..0509ac1 100644
--- a/convert.c
+++ b/convert.c
@@ -355,7 +355,7 @@ static int filter_buffer_or_fd(int in, int out, void *data)
 
 	sigchain_push(SIGPIPE, SIG_IGN);
 
-	if (params->src) {
+	if (params->fd == -1) {
 		write_err = (write_in_full(child_process.in, params->src, params->size) < 0);
 	} else {
 		write_err = copy_fd(params->fd, child_process.in);