[PATCH 1/2] exec: Restore EACCES of S_ISDIR execve()

[Kees Cook]

The return code for attempting to execute a directory has always been
EACCES. Adjust the S_ISDIR exec test to reflect the old errno instead
of the general EISDIR for other kinds of "open" attempts on directories.

Reported-by: Marc Zyngier <maz@xxxxxxxxxx>
Link: https://lore.kernel.org/lkml/20200813151305.6191993b@why
Fixes: 633fb6ac3980 ("exec: move S_ISREG() check earlier")
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 fs/namei.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/namei.c b/fs/namei.c
index 2112e578dccc..e99e2a9da0f7 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2849,8 +2849,10 @@ static int may_open(const struct path *path, int acc_mode, int flag)
 	case S_IFLNK:
 		return -ELOOP;
 	case S_IFDIR:
-		if (acc_mode & (MAY_WRITE | MAY_EXEC))
+		if (acc_mode & MAY_WRITE)
 			return -EISDIR;
+		if (acc_mode & MAY_EXEC)
+			return -EACCES;
 		break;
 	case S_IFBLK:
 	case S_IFCHR:
-- 
2.25.1