exec: restore EACCES of S_ISDIR execve()

Patch series "Fix S_ISDIR execve() errno".

Fix an errno change for execve() of directories, noticed by Marc Zyngier.
Along with the fix, include a regression test to avoid seeing this return
in the future.

This patch (of 2):

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.

Fixes: 633fb6ac3980 ("exec: move S_ISREG() check earlier")
Reported-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Greg Kroah-Hartman <gregkh@android.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@google.com>
Link: http://lkml.kernel.org/r/20200813231723.2725102-2-keescook@chromium.org
Link: https://lore.kernel.org/lkml/20200813151305.6191993b@why
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/namei.c b/fs/namei.c
index 2112e57..e99e2a9 100644 (file)
--- 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: