Commit 867bfa4a authored Jun 28, 2019 by Jann Horn Committed by Linus Torvalds Jun 29, 2019

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: 287980e4 ("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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 29b190fa

fs/binfmt_flat.c

+7 −16

Original line number	Diff line number	Diff line
		@@ -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 id, struct lib_info *libs)
		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 = kernel_read(bprm.file, bprm.buf, BINPRM_BUF_SIZE, &pos);

		res = prepare_binprm(&bprm);

		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);

Admin message