[PATCH v6 12/11] run-command: don't try to execute directories

[Brandon Williams <bmwill@google.com>]

In some situations run-command will incorrectly try (and fail) to
execute a directory instead of an executable.  For example:

Lets suppose a user has PATH=~/bin (where 'bin' is a directory) and they
happen to have another directory inside 'bin' named 'git-remote-blah'.
Then git tries to execute the directory:

	$ git ls-remote blah://blah
	fatal: cannot exec 'git-remote-blah': Permission denied

This is due to only checking 'access()' when locating an executable in
PATH, which doesn't distinguish between files and directories.  Instead
use 'stat()' and check that the path is to a regular file.  Now
run-command won't try to execute the directory 'git-remote-blah':

	$ git ls-remote blah://blah
	fatal: Unable to find remote helper for 'blah'

Signed-off-by: Brandon Williams <bmwill@google.com>
---
 run-command.c          | 3 ++-
 t/t0061-run-command.sh | 7 +++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/run-command.c b/run-command.c
index a97d7bf9f..ece0bf342 100644
--- a/run-command.c
+++ b/run-command.c
@@ -127,6 +127,7 @@ static char *locate_in_PATH(const char *file)
 
 	while (1) {
 		const char *end = strchrnul(p, ':');
+		struct stat st;
 
 		strbuf_reset(&buf);
 
@@ -137,7 +138,7 @@ static char *locate_in_PATH(const char *file)
 		}
 		strbuf_addstr(&buf, file);
 
-		if (!access(buf.buf, F_OK))
+		if (!stat(buf.buf, &st) && S_ISREG(st.st_mode))
 			return strbuf_detach(&buf, NULL);
 
 		if (!*end)
diff --git a/t/t0061-run-command.sh b/t/t0061-run-command.sh
index 98c09dd98..30c4ad75f 100755
--- a/t/t0061-run-command.sh
+++ b/t/t0061-run-command.sh
@@ -37,6 +37,13 @@ test_expect_success !MINGW 'run_command can run a script without a #! line' '
 	test_cmp empty err
 '
 
+test_expect_success 'run_command should not try to execute a directory' '
+	test_when_finished "rm -rf bin/blah" &&
+	mkdir -p bin/blah &&
+	PATH=bin:$PATH test_must_fail test-run-command run-command blah 2>err &&
+	test_i18ngrep "No such file or directory" err
+'
+
 test_expect_success POSIXPERM 'run_command reports EACCES' '
 	cat hello-script >hello.sh &&
 	chmod -x hello.sh &&
-- 
2.13.0.rc0.306.g87b477812d-goog