From: Jann Horn <jannh@google.com>
To: Andrew Morton <akpm@linux-foundation.org>, jannh@google.com
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
Kees Cook <keescook@chromium.org>,
Nicolas Pitre <nicolas.pitre@linaro.org>,
Arnd Bergmann <arnd@arndb.de>,
Geert Uytterhoeven <geert@linux-m68k.org>,
linux-m68k@lists.linux-m68k.org,
Russell King <linux@armlinux.org.uk>,
linux-arm-kernel@lists.infradead.org
Subject: [PATCH] binfmt_flat: make load_flat_shared_library() work
Date: Fri, 24 May 2019 22:18:17 +0200 [thread overview]
Message-ID: <20190524201817.16509-1-jannh@google.com> (raw)
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.
Cc: stable@vger.kernel.org
Fixes: 287980e49ffc ("remove lots of IS_ERR_VALUE abuses")
Signed-off-by: Jann Horn <jannh@google.com>
---
I only found the bug by looking at the code, I have not verified its
existence at runtime.
Also, this patch is compile-tested only.
It would be nice if someone who works with nommu Linux could have a
look at this patch.
akpm's tree is the right one for this patch, right?
fs/binfmt_flat.c | 23 +++++++----------------
1 file changed, 7 insertions(+), 16 deletions(-)
diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c
index 82a48e830018..e4b59e76afb0 100644
--- a/fs/binfmt_flat.c
+++ b/fs/binfmt_flat.c
@@ -856,9 +856,14 @@ static int load_flat_file(struct linux_binprm *bprm,
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);
--
2.22.0.rc1.257.g3120a18244-goog
next reply other threads:[~2019-05-24 20:18 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-24 20:18 Jann Horn [this message]
2019-05-25 21:43 ` [PATCH] binfmt_flat: make load_flat_shared_library() work Andrew Morton
2019-05-27 13:38 ` Jann Horn
2019-05-27 14:37 ` Nicolas Pitre
2019-05-28 10:56 ` Greg Ungerer
2019-05-29 11:52 ` Arnd Bergmann
2019-05-28 10:56 ` Greg Ungerer
2019-05-29 12:05 ` Arnd Bergmann
2019-05-29 12:29 ` Greg Ungerer
2019-05-29 13:41 ` Arnd Bergmann
2019-06-02 7:21 ` Sergei Poselenov
2019-05-29 12:32 ` John Paul Adrian Glaubitz
2019-05-29 12:38 ` Jann Horn
2019-05-29 12:47 ` John Paul Adrian Glaubitz
2019-05-29 12:40 ` Greg Ungerer
2019-05-29 13:16 ` Andreas Schwab
2019-05-29 13:18 ` John Paul Adrian Glaubitz
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