From: Alyssa Ross <hi@alyssa.is>
To: Alexander Viro <viro@zeniv.linux.org.uk>,
Christian Brauner <brauner@kernel.org>
Cc: Kees Cook <keescook@chromium.org>,
Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
Eric Biederman <ebiederm@xmission.com>,
linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: [PATCH] exec: allow executing block devices
Date: Tue, 10 Oct 2023 09:21:33 +0000 [thread overview]
Message-ID: <20231010092133.4093612-1-hi@alyssa.is> (raw)
As far as I can tell, the S_ISREG() check is there to prevent
executing files where that would be nonsensical, like directories,
fifos, or sockets. But the semantics for executing a block device are
quite obvious — the block device acts just like a regular file.
My use case is having a common VM image that takes a configurable
payload to run. The payload will always be a single ELF file.
I could share the file with virtio-fs, or I could create a disk image
containing a filesystem containing the payload, but both of those add
unnecessary layers of indirection when all I need to do is share a
single executable blob with the VM. Sharing it as a block device is
the most natural thing to do, aside from the (arbitrary, as far as I
can tell) restriction on executing block devices. (The only slight
complexity is that I need to ensure that my payload size is rounded up
to a whole number of sectors, but that's trivial and fast in
comparison to e.g. generating a filesystem image.)
Signed-off-by: Alyssa Ross <hi@alyssa.is>
---
fs/exec.c | 6 ++++--
fs/namei.c | 2 +-
2 files changed, 5 insertions(+), 3 deletions(-)
diff --git a/fs/exec.c b/fs/exec.c
index 6518e33ea813..e29a9f16da5f 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -148,7 +148,8 @@ SYSCALL_DEFINE1(uselib, const char __user *, library)
* and check again at the very end too.
*/
error = -EACCES;
- if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode) ||
+ if (WARN_ON_ONCE((!S_ISREG(file_inode(file)->i_mode) &&
+ !S_ISBLK(file_inode(file)->i_mode)) ||
path_noexec(&file->f_path)))
goto exit;
@@ -931,7 +932,8 @@ static struct file *do_open_execat(int fd, struct filename *name, int flags)
* and check again at the very end too.
*/
err = -EACCES;
- if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode) ||
+ if (WARN_ON_ONCE((!S_ISREG(file_inode(file)->i_mode) &&
+ !S_ISBLK(file_inode(file)->i_mode)) ||
path_noexec(&file->f_path)))
goto exit;
diff --git a/fs/namei.c b/fs/namei.c
index 567ee547492b..60c89321604a 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3254,7 +3254,7 @@ static int may_open(struct mnt_idmap *idmap, const struct path *path,
fallthrough;
case S_IFIFO:
case S_IFSOCK:
- if (acc_mode & MAY_EXEC)
+ if ((inode->i_mode & S_IFMT) != S_IFBLK && (acc_mode & MAY_EXEC))
return -EACCES;
flag &= ~O_TRUNC;
break;
base-commit: 94f6f0550c625fab1f373bb86a6669b45e9748b3
--
2.42.0
next reply other threads:[~2023-10-10 9:25 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-10 9:21 Alyssa Ross [this message]
2023-10-10 22:48 ` [PATCH] exec: allow executing block devices Kees Cook
2023-10-11 7:38 ` Alyssa Ross
2023-10-11 15:59 ` Kees Cook
2023-10-20 6:06 ` kernel test robot
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