[PATCH 4.19 34/72] fs/binfmt_flat.c: make load_flat_shared_library() work

From: Greg Kroah-Hartman
Date: Tue Jul 02 2019 - 04:06:37 EST

From: Jann Horn <jannh@xxxxxxxxxx>

commit 867bfa4a5fcee66f2b25639acae718e8b28b25a5 upstream.

load_flat_shared_library() is broken: It only calls load_flat_file() if
prepare_binprm() returns zero, but prepare_binprm() returns the number of
bytes read - so this only happens if the file is empty.

Instead, call into load_flat_file() if the number of bytes read is
non-negative. (Even if the number of bytes is zero - in that case,
load_flat_file() will see nullbytes and return a nice -ENOEXEC.)

In addition, remove the code related to bprm creds and stop using
prepare_binprm() - this code is loading a library, not a main executable,
and it only actually uses the members "buf", "file" and "filename" of the
linux_binprm struct. Instead, call kernel_read() directly.

Link: http://lkml.kernel.org/r/20190524201817.16509-1-jannh@xxxxxxxxxx
Fixes: 287980e49ffc ("remove lots of IS_ERR_VALUE abuses")
Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Nicolas Pitre <nicolas.pitre@xxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
Cc: Russell King <linux@xxxxxxxxxxxxxxx>
Cc: Greg Ungerer <gerg@xxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

fs/binfmt_flat.c | 23 +++++++----------------
1 file changed, 7 insertions(+), 16 deletions(-)

--- a/fs/binfmt_flat.c
+++ b/fs/binfmt_flat.c
@@ -856,9 +856,14 @@ err:

static int load_flat_shared_library(int id, struct lib_info *libs)
+ /*
+ * This is a fake bprm struct; only the members "buf", "file" and
+ * "filename" are actually used.
+ */
struct linux_binprm bprm;
int res;
char buf[16];
+ loff_t pos = 0;

memset(&bprm, 0, sizeof(bprm));

@@ -872,25 +877,11 @@ static int load_flat_shared_library(int
if (IS_ERR(bprm.file))
return res;

- bprm.cred = prepare_exec_creds();
- res = -ENOMEM;
- if (!bprm.cred)
- goto out;
- /* We don't really care about recalculating credentials at this point
- * as we're past the point of no return and are dealing with shared
- * libraries.
- */
- bprm.called_set_creds = 1;
- res = prepare_binprm(&bprm);
+ res = kernel_read(bprm.file, bprm.buf, BINPRM_BUF_SIZE, &pos);

- if (!res)
+ if (res >= 0)
res = load_flat_file(&bprm, libs, id, NULL);

- abort_creds(bprm.cred);