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); - -out: allow_write_access(bprm.file); fput(bprm.file);
