From: Jann Horn jannh@google.com Subject: fs/binfmt_flat.c: make load_flat_shared_library() work

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@google.com Fixes: 287980e49ffc ("remove lots of IS_ERR_VALUE abuses") Signed-off-by: Jann Horn jannh@google.com Cc: Alexander Viro viro@zeniv.linux.org.uk Cc: Kees Cook keescook@chromium.org Cc: Nicolas Pitre nicolas.pitre@linaro.org Cc: Arnd Bergmann arnd@arndb.de Cc: Geert Uytterhoeven geert@linux-m68k.org Cc: Russell King linux@armlinux.org.uk Cc: Greg Ungerer gerg@linux-m68k.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

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

--- a/fs/binfmt_flat.c~binfmt_flat-make-load_flat_shared_library-work +++ a/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); - -out: allow_write_access(bprm.file); fput(bprm.file);

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